Claims for Patent: 5,104,888

Summary for Patent: 5,104,888

Title:	Thiazolidine derivatives, their preparation and use
Abstract:	Compounds of formula (I): ##STR1## (in which R1 -R7 are hydrogen or various organic groups, n is 1-10, Ar is an aromatic group, U is CH2 or a carbon atom doubly bonded to either one of its adjacent carbons, and W is >CH2, >C═O, >CHOH, >C═NOH or various derivatives thereof) have the ability to lower the levels of blood lipid peroxides and blood sugars and to inhibit the activity of aldose reductase; they may be used therapeutically for these purposes.
Inventor(s):	Takao Yoshioka, Eiichi Kitazawa, Yomoyuki Kurumada, Mitsuo Yamazaki, Kazuo Hasegawa, Takashi Fujita
Assignee:	Sankyo Co Ltd
Application Number:	US07/560,466
Patent Claims:	1. A compound of formula (I): ##STR619## in which: R1 represents a hydrogen atom, a C1 -C10 alkyl group or a C7 -C13 aralkyl group;R2 represents a hydrogen atom or a C1 -C5 alkyl group; R3 represents a hydrogen atom, a C1 -C23 alkanoyl group, a C3 -C23 alkenoyl group, a C3 -C23 alkynoyl group, a substituted C1 -C23 alkanoyl, C3 -C23 alkenoyl or C3 -C23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl, a 5 to 8-membered heterocyclic acyl group having 1 to 3 hetero atoms of N, S or O, a group of formula --SO3 R8 where R6 represents a hydrogen atom, an aralkyl group where the alkyl part is C1 -C3 alkyl, a C1 -C5 alkyl group or a C1 -C5 alkyl group having at least one substituent selected from the group consisting of hydroxy groups and C1 -C5 alkoxy groups, a C1 -C10 alkyl group or a substituted C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (b); R4 represents a hydrogen atom, a C1 -C10 alkyl group or a C1 -C5 alkoxy group; R5 represents a hydrogen atom, a C1 -C5 alkyl group or a C1 -C5 alkoxy group; R6 and R7 are independently selected from the group consisting of hydrogen atoms, C1 -C10 alkyl groups and substituted C1 -C10 alkyl groups having at least one substituent selected from the group consisting of substituents (b); Ar is a divalent group selected from the group consisting of divalent carbocyclic aromatic groups, and divalent heterocyclic aromatic groups formed from a pyridine, furan, thiophene or pyrrole ring; W represents a --CH2 -- group, a >C═O group, a group of formula >CH--OR11 wherein R11 represents a hydrogen atom, a C1 -C23 alkanoyl group, a C3 -C23 alkenoyl group, a C3 -C23 alkynoyl group, a substituted C1 -C23 alkanoyl, C3 -C23 alkenoyl or C3 -C23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and napthoyl, a 5-8 membered heterocyclia acyl having 1 to 3 heteroatoms of N, S, or O, A C1 -C10 alkyl group or a substituted C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (b), or a group of formula >C═N--O--R12 in which R12 represents a hydrogen atom, a C1 -C10 alkyl group, a C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (b), a C1 -C23 alkanoyl group, a C3 -C23 alkenoyl group, a C3 -C23 alkynoyl group, a substituted C1 -C23 alkanoyl, C3 -C23 alkenoyl or C3 -C23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl or a heterocyclic acyl group having 1 to 3 heteroatoms of N, S or O; U represents a --CH2 -- group; or W and U together represent a group of formula --CH═CH--; or when W represents a carbonyl group or said group of formula >C═N--OR12, U, R1 and the carbon atom to which R1 is attached together represent a group of formula --CH═C<; n is an integer of from 1 to 3; said aryl groups and the aryl parts of said aralkyl, aralkyloxycarbonyl, and aromatic acyloxy being C6 -C10 carbocyclic aryl groups which are unsubstituted or have at least one substituent selected from the group consisting of substituents (c); said heterocyclic groups, heterocyclic parts of said heterocyclic acyl and acyloxy groups have from 5 to 10 ring atoms, of which from 1 to 5 are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic groups being unsubstituted or having at least one substituent selected from the group consisting of substituents (d); said substituents (a) being selected from the group consisting of aryl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and aralkyloxycarbonyl groups; said substituents (b) being selected from the group consisting of hydroxy groups, C1 -C5 alkoxy groups, aryl groups, C1 -C23 alkanoyloxy groups, C3 -C23 alkenoyloxy groups, C3 -C23 alkynoyloxy groups, substituted C1 -C23 alkanoyloxy, C3 -C23 alkenoyloxy or C3 -C23 alkynoyloxy groups having at least one substituent selected from the group consisting of substituents (a), aromatic acyloxy groups, heterocyclic acyloxy groups, groups of formula --COOR8 where R8 is as defined above and groups of formula --CONR9 R10 whereR9 and R10 are independently selected from the group consisting of hydrogen atoms and C1 -C5 alkyl groups or R9 and R10, together with the nitrogen atom to which they are attached, represent a heterocyclic group having from 5 to 7 ring atoms of which from 1 to 3 atoms, including nitrogen atom, are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted, or, where said ring atoms include an additional nitrogen hetero-atom, said additional nitrogen atom being unsubstituted or having a single substituent selected from the group consisting of substituents (e); said substituents (c) being selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups, C1 -C5 alkyl groups having at least one halogen substituent, halogen atoms, amino groups, C1 -C5 alkylamino groups, dialkylamino groups in which each alkyl part is C1 -C5, nitro groups, cyano groups, groups of formula --CONR2 where R represents a C1 -C5 alkyl group or an aryl group and hydroxy groups; and said substituents (d) being selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and doubly bonded oxygen atoms; said substituents (e) being selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkanoyl groups, C3 -C5 alkenoyl groups and C3 -C5 alkynoyl groups; provided that:(α) where: R3 represents said hydrogen atom, an unsubstituted C1 -C6 alkanoyl group, an unsubstituted C3 -C6 alkenoyl group, an unsubstituted C3 -C6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group; and R6 and R7 both represent hydrogen atoms; and Ar represents a p-phenylene group; and W represents a group of formula >CH2, >C═O or >CH--OR11x (wherein R11x represents a hydrogen atom, an unsubstituted C1 -C6 alkanoyl group, an unsubstituted C3 -C6 alkenoyl group, an unsubstituted C3 -C6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group); and U represents said group of formula >CH2, then(i) when R1 represents a hydrogen atom or a C1 -C5 alkyl group, R4 represents a C6 -C10 alkyl group, and (ii) when R4 represents a hydrogen atom, a C1 -C5 alkyl group or a C1 -C5 alkoxy group, R1 represents a C6 -C10 alkyl group or said C7 -C13 aralkyl group; (β) where: R1 and R2 are independently selected from the group consisting of hydrogen atoms and C1 -C5 alkyl groups; and R4 and R5 are independently selected from the group consisting of hydrogen atoms, C1 -C5 alkyl groups and C1 -C5 alkoxy groups; and Ar represents a p-phenylene group; and W is a group of formula >CH2, >C═O or >CH--OR11x (where R11x is as defined above); and U represents said group of formula >CH2 ; and n is an integer from 1 to 3, then at least one of R3, R6 and R7 represents said alkyl or substituted alkyl group; and pharmaceutically acceptable salts thereof. 2. A compound as claimed in claim 1, in which:R1 represents a hydrogen atom or a C1 -C10 alkyl group; R2 represents a hydrogen atom or a C1 -C3 alkyl group; R3 represents a hydrogen atom, a sulfo group, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C6 -C10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R13 --(CH2)m --CO--, whereR13 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (g), and m is an integer from 1 to 5, a group of formula Het--CO--, whereHet represents a heterocyclic group having 5 to 6 ring atoms, of which from 1 to 3 are hetero-atoms selected from the group consisting of nitrogen oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted or having at least one substituent selected from the group consisting of C1 -C5 alkyl groups, a C1 -C5 alkyl group, a C1 -C5 alkyl group substituted by a group of formula --COOR8a, whereR8a represents a hydrogen atom, a C1 -C5 alkyl group or an alkoxyalkyl group were both the alkoxy part and the alkyl part are C1 -C5, a C2 -C5 hydroxyalkyl group, a C2 -C5 alkyl group substituted by a group of formula --O--CO--R53, whereR53 represents a C1 -C10 alkyl group, a phenyl group, a phenyl group having at least one substituent selected from the group consisting of substituents (g) or a heterocyclic group Het, as defined above, or a C1 -C3 alkyl group substituted by a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (g) are selected from the group consisting of C1 -C5 alkyl groups, trifluoromethyl groups, C1 -C5 alkoxy groups, halogen atoms, nitro groups, amino groups, hydroxy groups and dialkylamino groups where each alkyl part is C1 -C5 ; said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C1 -C4, dialkylcarbamoyl groups where each alkyl part is C1 -C4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; R4 represents a C1 -C10 alkyl group or a methoxy group; R5 represents a hydrogen atom, a C1 -C5 alkyl group or a methoxy group; R6 and R7 are independently selected from the group consisting of hydrogen atoms, C1 -C5 alkyl groups, C1 -C5 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined above, C2 -C5 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a group of formula --O--CO--R53 where R53 is as defined above, and C1 -C3 alkyl groups having a single substituent selected from the group consisting of substituents (h); Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH2)n --O-- at its 2-position and is attached to the --CH2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a C1 -C3 alkyl substituent; W represents a group of formula --CH2 --, >C═O, >CH--OR11 or >C═N--OR12 whereR11 represents a hydrogen atom, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C6 -C10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R13 --(CH2)m --CO-- where R13 and m are as defined above or a group of formula Het--CO-- where Het is as defined above, and R12 represents a hydrogen atom, a C1 -C5 alkyl group, a C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (j), a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C6 -C10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), or said group of formula R13 --CH2)m --CO-- or Het--CO--; and said substituents (j) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (g), C2 -C11 alkanoyloxy groups, C2 -C11 alkanoyloxy groups substituted by a group of formula --COOR8a where R8a is as defined above, C3 -C11 alkenoyloxy groups substituted by a group of formula --COOR8a where R8a is as defined above, phenylalkenoyloxy groups where the alkenyl part is C2 -C10 and the phenyl part is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (g), groups of formula --COOR8a where R8a is as defined above, benzyloxycarbonyl groups and groups of formula --COR9 R10 where R9 and R10 are as defined above; U represents(i) where W represents a group of formula --CH2 --, >C═O, >CH2 OR11 or >C═N--OR12, a group of formula --CH2 --, (ii) with W, a group of formula --CH═CH--, or (iii) where W represents a group of formula >C═O or >C═N--OR14, in which R14 represents any one of the acyl groups defined for R12, with R1 and the carbon atom to which R1 is attached, a group of formula --CH═C<. 3. A compound as claimed in claim 2, in which:R1, R2, R4, R5, Ar, W and U are defined in claim 2; R6 and R7 both represent hydrogen atoms; R3 and R11 are independently selected from the group consisting of hydrogen atoms, C1 -C10 alkanoyl groups, C3 -C10 alkenoyl groups, C1 -C10 alkanoyl or C3 -C10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 2, arylcarbonyl groups as defined in claim 2, and groups of formulae R13 --(CH2)m --CO-- and Het--CO-- where R13, m and Het are as defined in claim 2; and R12 represents any one of the groups or atoms defined for R3 and R11 or a C1 -C5 alkyl group of a C1 -C3 alkyl group having at least one substituent selected from the group consisting of substituents (f) defined in claim 2. 4. A compound as claimed in claim 2, in which:R1, R2, R4, R5, Ar, W and U are as defined in claim 2; R3, R6, R7 and R12 are independently selected from the group consisting of hydrogen atoms, C1 -C5 alkyl groups, C1 -C5 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 2, C2 -C5 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a group of formula --O--CO--R53 where R53 is as defined in claim 2 and C1 -C3 alkyl groups substituted by a single substituent selected from the group consisting of substituents (h) as defined in claim 2; and R11 represents a hydrogen atom, an acetyl group or a benzoyl group; or R12 represents a hydrogen atom, a C1 -C5 alkyl group, a C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (k), a C2 -C6 alkanoyl group, a C2 -C10 alkanoyl group having at least one substituent selected from the group consisting of substituents (l), a C3 -C5 alkenoyl group, a C3 -C5 alkenoyl group having at least one substituent selected from the group consisting of substituents (l), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (m), a pyridinecarbonyl group, a furoyl group, a thenoyl group or a pyridinecarbonyl, furoyl or thenoyl group having at least one substituent selected from the group consisting of C1 -C5 alkyl groups; said substituents (k) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (m), C2 -C5 alkanoyloxy groups, C2 -C10 alkanoyloxy or C3 -C10 alkenoyloxy groups substituted by a group of formula --COOR8a where R8a is as defined in claim 2, C3 -C10 alkenoyloxy groups substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (m), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (m), groups of formula --COOR8a where R8a is as defined in claim 2 and substituents (h) as defined in claim 2; said substituents (l) are selected from the group consisting of phenyl groups, carboxy groups, alkoxycarbonyl groups where the alkoxy part is C1 -C5 and benzyloxycarbonyl groups; and said substituents (m) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups, halogen atoms and trifluoromethyl groups. 5. A compound as claimed in claim 1, in which:R1 represents an alkyl group selected from the group consisting of methyl, ethyl, isobutyl, pentyl, hexyl, 3,3-dimethylbutyl, heptyl, 4,4-dimethylpentyl, octyl, 5,5-dimethylhexyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (n), an aralkanoyl group of formula R15 --(CH2)m --CO--where R15 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (n), and m is an integer from 1 to 5, a pyridinecarbonyl group, a furoyl group, a thenoyl group, a C1 -C3 alkyl group, a C1 -C3 alkyl group substituted by a group of formula --COOR8a whereR8a represents a hydrogen atom, a C1 -C5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C1 -C5, a C2 -C3 hydroxyalkyl group, a C1 -C5 alkyl group substituted by a C1 -C5 alkoxy group, a C2 -C5 alkyl group substituted by a C2 -C4 alkanoyloxy or a benzoyloxy group or a methyl group having a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (n) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and halogen atoms; R4 represents a C1 -C10 alkyl group; R5 represents a hydrogen atom or a C1 -C3 alkyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms, C1 -C3 alkyl groups, C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined above, C2 -C3 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a C2 -C4 alkanoyloxy of a benzoyloxy group, and methyl groups substituted by a single substituent selected from the group consisting of substituents (h); said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C1 -C4, dialkylcarbamoyl groups where each alkyl part is C1 -C4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH2)n --O-- at its 2-position and is attached to the --CH2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a methyl substituent; W represents a group of formula --CH2 --, >C═O, >CH--OR11 or >C═N--OR12, where:R11 represents a hydrogen atom or any one of the acyl groups defined above for R3 ; and R12 represents a benzyl group, any one of the groups or atoms defined above for R3, a pyridinecarbonyl group or a pyridinecarbonyl group having at least one substituent selected from the group consisting of C1 -C5 alkyl groups; and U represents(i) where W represents a group of formula --CH2 --, >C═O, >CH--OR11 or >C═N--OR12 , a group of formula --CH2 --, (ii) with W, a group of formula --CH═CH--, or (iii) where W represents a group of formula >C═O, with R1 and the carbon atom to which R1 is attached, a group of formula --CH═C<. 6. A compound as claimed in claim 5, in which:R1, R2, R4, R5, Ar, W and U are as defined in claim 5; R6 and R7 are both hydrogen atoms; R3 and R11 are independently selected from the group consisting of hydrogen atoms, C1 -C10 alkanoyl groups, C3 -C10 alkenoyl groups, C1 -C10 alkanoyl or C3 -C10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 5, benzoyl groups, benzoyl groups having at least one substituent selected from the group consisting of substituents (n) as defined in claim 5, groups of formula R15 --(CH2)m --CO-- where R15 and m are as defined in claim 5, pyridinecarbonyl groups, furoyl groups and thenoyl groups; and R12 represents a hydrogen atom, a methyl group, a benzyl group, a t-butoxycarbonylmethyl group or any one of the acyl groups defined above for R3 and R11. 7. A compound as claimed in claim 5, in which:R1, R2, R4, R5, Ar, W and U are as defined in claim 5; R3, R6 R7 are independently selected from the group consisting of C1 -C3 alkyl groups, C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 5, C2 -C3 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a C2 -C4 alkanoyloxy or a benzoyloxy group, and methyl groups having a single substituent selected from the group consisting of substituents (h) as defined in claim 5; R11 represents a hydrogen atom; R12 represents a hydrogen atom, a C1 -C3 alkyl group having at least one substituent selected from the group consisting of substituents (o), a C2 -C4 alkanoyl group, a C2 -C4 alkanoyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 5, an acryloyl group, an acryloyl group having a β-substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (q), a pyridinecarbonyl group, a pyridinecarbonyl group having at least one substituent selected from the group consisting of C1 -C5 alkyl groups or any one of the groups defined above for R3, R6 and R7 ; said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and benzyloxycarbonyl groups; and said substituents (o) are selected from the group consisting of carboxy groups and alkoxycarbonyl groups where the alkoxy part is C1 -C5 ; said substituents (q) are selected from the group consisting of methyl groups, ethyl groups, methoxy groups and ethoxy groups. 8. A compound as claimed in claim 1 in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO--where R16 represents a hydrogen atom or a C1 -C5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R17 OOC.CH═CH--CO--where R17 represents a hydrogen atom, a C1 -C5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a whereR8a represents a hydrogen atom, a C1 -C5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C1 -C5 ; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms and C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined above; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O, >C═N--OH, >C═N--OCH2 COOH or >C═N--OCOR18 where R18 represents a C1 -C5 alkyl group; and U represents a group of formula --CH2 --. 9. A compound as claimed in claim 8, in which:R1, R2, R4, R5, Ar and U are as defined in claim 8; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, a C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO-- where R16 and m are as defined in claim 8, a cis or trans- group of formula R17 OOC.CH═CH--CO-- where R17 is as defined in claim 8, or a 2-, 3- or 4-pyridinecarbonyl group; R6 and R7 are both hydrogen atoms; W represents a group of formula >C═NOR12 whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 8, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R3, R6 and R7 ; and n is 1 or 2. 10. A compound as claimed in claim 8, in which:R1, R2, R4, R5, Ar and U are as defined in claim 8; R3, R6 and R7 are independently selected from the group consisting of C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 8; W represents a group of formula >CH2, >C═O or >C═NOR12 ;R12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 8, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R3, R6 and R7 ; and n is 1 or 2. 11. A compound as claimed in claim 2, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f) as defined in claim 2, an arylcarbonyl group as defined in claim 2, a group of formula R13 --(CH2)m --CO-- or Het--CO-- where R13, m and Het are as defined in claim 2 or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 2; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 represents a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 2; R7 represents a hydrogen atom or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 2; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula >CH2, >C═O or >C═NOR12, whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 2, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 2; U represents a group of formula --CH2 --; and n is 1 or 2. 12. A compound as claimed in claim 2, in which:R1 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO--where R14 represents a hydrogen atom or a C1 -C5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R17 OOC.CH═CH--CO--where R17 represents a hydrogen atom, C1 -C5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 2; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms and C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 2; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O or >C═N--OR12, whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 2, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C1 -C5 alkyl group, a C1 -C5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R3, R6 and R7 ; said substituents (n) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and halogen atoms; and U represents a group of formula --CH2 --. 13. A compound as claimed in claim 2, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO--where R16 represents a hydrogen atom or a C1 -C5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R17 OOC.CH═CH--CO--where R17 represents a hydrogen atom, a C1 -C5 alkyl group of a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 2; R4 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms and C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 2; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O or >C═N--OR12 whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 2, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C1 -C5 alkyl group, a C1 -C5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R3, R6 and R7 ; said substituents (n) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and halogen atoms; and U represents a group of formula --CH2 --. 14. A compound as claimed in claim 2, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents C1 -C3 alkyl group substituted by a group of formula --COOR8a, where R8a is as defined in claim 2; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O, >C═N--OH, or >C═N--O--(C1 -C3 alkyl)--COOR8a where R8a is as defined in claim 2; U represents a group of formula --CH2 --; and n is 1 or 2. 15. A compound as claimed in claim 2, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents --CH2 --COO(C1 -C5 alkyl) group; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O, >C═N--OH, or >C═N--O--(C1 -C3 alkyl)--COO(C1 -C5 alkyl); U represents a group of formula --CH2 --; and n is 1 or 2. 16. The compound as claimed in claim 1, which is 5-[4-(6-Hydroxy-5,7,8-trimethyl-2-octylchroman-2-ylmethoxy)benzyl]thiazolidine-2,4-dione and pharmaceutically acceptable salts thereof. 17. The compound as claimed in claim 1, which is 5-{4-[6-Hydroxy-4-(E)-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy]benzyl}thiazolidine-2,4-dione and pharmaceutically acceptable salts thereof. 18. The compound as claimed in claim 1, which 5-{4-[6-Acetoxy-4-(E)-acetoxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy]benzyl}thiazolidine-2,4-dione and pharmaceutically acceptable salts thereof. 19. The compound as claimed in claim 1, which is α-{5-[4-(6-Carboxymethoxy-2,5,7,8-tetramethyl-4-oxochroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid and pharmaceutically acceptable salts thereof. 20. The compound as claimed in claim 1, which is α-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid and pharmaceutically acceptable salts thereof. 21. The compound as claimed in claim 1, which is α,α'-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidine-3,5-diyl}diacetic acid and pharmaceutically acceptable salts thereof. 22. A pharmaceutical composition for the treatment of hyperlipaemia or hyperglycaemia, comprising an effective amount of an active compound in combination with a pharmaceutically acceptable carrier or diluent, wherein the active compound is selected from the group consisting of compounds of formula (1): ##STR620## in which: R1 represents a hydrogen atom, a C1 -C10 alkyl group or a C7 -C13 aralkyl group;R2 represents a hydrogen atom or a C1 -C5 alkyl group; R3 represents a hydrogen atom, a C1 -C23 alkanoyl group, a C3 -C23 alkenoyl group, a C3 -C23 alkynoyl group, a substituted C1 -C23 alkanoyl, C3 -C23 alkenoyl or C3 -C23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl, a 5 to 8-membered heterocyclic acyl group having 1 to 3 hetero atoms of N, S or O, a group of formula --SO3 R8 where R8 represents a hydrogen atom, an aralkyl group where the alkyl part is C1 -C3 alkyl, a C1 -C5 alkyl group or a C1 -C5 alkyl group having at least one substituent selected from the group consisting of hydroxy groups and C1 -C5 alkoxy groups, a C1 -C10 alkyl group or a substituted C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (b); R4 represents a hydrogen atom, a C1 -C10 alkyl group or a C1 -C5 alkoxy group; R5 represents a hydrogen atom, a C1 -C5 alkyl group or a C1 -C5 alkoxy group; R6 and R7 are independently selected for the group consisting of hydrogen atoms, C1 -C10 alkyl groups and substituted C1 -C10 alkyl groups having at least one substituent selected from the group consisting of substituents (b); Ar is a divalent group selected from the group consisting of divalent carbocyclic aromatic groups, and divalent heterocyclic aromatic groups formed from a pyridine, furan, thiophene or pyrrole ring; W represents a --CH2 -- group, a >C═O group, a group of formula >CH--OR11 where R11 represents a hydrogen atom, a C1 -C23 alkanoyl group, a C3 -C23 alkenoyl group, a C3 -C23 alkynoyl group, a substituted C1 -C23 alkanoyl, C3 -C23 alkenoyl or C3 -C23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and napthoyl, a 5-8 membered heterocyclia acyl having 1 to 3 heteroatoms of N, S, or O, A C1 -C10 alkyl group or a substituted C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (b), or a group of formula >C═N--O--R12 in which R12 represents a hydrogen atom, a C1 -C10 alkyl group, a C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (b), a C1 -C23 alkanoyl group, a C3 -C23 alkenoyl group, a C3 -C23 alkynoyl group, a substituted C1 -C23 alkanoyl, C3 -C23 alkenoyl or C3 -C23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl or a heterocyclic acyl group having 1 to 3 heteroatoms of N, S or O; U represents a --CH2 -- group; or W and U together represent a group of formula --CH═CH--; or when W represents a carbonyl group of said group of formula >C═N--OR12, U, R1 and the carbon atom to which R1 is attached together represent a group of formula --CH═C<; n is an integer of from 1 to 3; said aryl groups and the aryl parts of said aralkyl, aralkyloxycarbonyl, and aromatic acyloxy being C6 -C10 carbocyclic aryl groups which are unsubstituted or have at least one substituent selected from the group consisting of substituents (c); said heterocyclic groups, heterocyclic parts of said heterocyclic acyl and acyloxy groups have from 5 to 10 ring atoms, of which 1 to 5 are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic groups being unsubstituted or having at least one substituent selected from the group consisting of substituents (d); said substituents (a) being selected from the group consisting of aryl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and aralkyloxycarbonyl groups; said substituents (b) being selected from the group consisting of hydroxy groups, C1 -C5 alkoxy groups, aryl groups, C1 -C23 alkanoyloxy groups, C3 -C23 alkenoyloxy groups, C3 -C23 alkynoyloxy groups, substituted C1 -C23 alkanoyloxy, C3 -C23 alkenoyloxy or C3 -C23 alkynoyloxy groups having at least one substituent selected from the group consisting of substituents (a), aromatic acyloxy groups, heterocyclic acyloxy groups, groups of formula --COOR8 where R8 is as defined above and groups of formula --CONR9 R10 whereR9 and R10 are independently selected from the group consisting of hydrogen atoms and C1 -C5 alkyl groups or R9 and R10, together with the nitrogen atom to which they are attached, represent a heterocyclic group having from 5 to 7 ring atoms of which from 1 to 3 atoms, including said nitrogen atom, are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted, or, where said ring atoms include an additional nitrogen hetero-atom, said additional nitrogen atom being unsubstituted or having a single substituent selected from the group consisting of substituents (e); said substituents (c) being selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups, C1 -C5 alkyl groups having at least one halogen substituent, halogen atoms, amino groups, C1 -C5 alkylamino groups, dialkylamino groups in which each alkyl part is C1 -C5, nitro groups, cyano groups, groups of formula --CONR2 where R represents a C1 -C5 alkyl group or an aryl group and hydroxy groups; and said substituents (d) being selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and doubly bonded oxygen atoms; said substituents (e) being selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkanoyl groups, C3 -C5 alkenoykl groups and C3 -C5 alkynoyl groups; provided that: (α) where: R3 represents said hydrogen atom, an unsubstituted C1 -C6 alkanoyl group, an unsubstituted C3 -C6 alkenoyl group, an unsubstituted C3 -C6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group; and R6 and R7 both represent hydrogen atoms; and Ar represents a p-phenylene group; and W represents a group of formula >CH2, >C═O or >CH--OR11x (wherein R11x represents a hydrogen atom, an unsubstituted C1 -C6 alkanoyl group, an unsubstituted C3 -C6 alkenoyl group, an unsubstituted C3 -C6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group); and U represents said group of formula >CH2, then(i) when R1 represents a hydrogen atom or a C1 -C5 alkyl group, R4 represents a C6 -C10 alkyl group, and (ii) when R4 represents a hydrogen atom, a C1 -C5 alkyl group or a C1 -C5 alkoxy group, R1 represents a C6 -C10 alkyl group or said C7 -C13 aralkyl group; or (β) where: R1 and R2 are independently selected from the group consisting of hydrogen atoms and C1 -C5 alkyl groups; and R4 and R5 are independently selected from the group consisting of hydrogen atoms, C1 -C5 alkyl groups and C1 -C5 alkoxy groups; and Ar represents a p-phenylene group; and W is a group of formula >CH2, >C═O or >CH--OR11x (where R11x is as defined above); and U represents said group of formula >CH2 ; and n is an integer from 1 to 3, then at least one of R3, R6 and R7 represents said alkyl or substituted alkyl group; and pharmaceutically acceptable salts thereof. 23. A composition as claimed in claim 22, in which:R1 represents a hydrogen atom or a C1 -C10 alkyl group; R2 represents a hydrogen atom or a C1 -C3 alkyl group; R3 represents a hydrogen atom, a sulfo group, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C6 -C10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R13 --(CH2)m --CO--, whereR13 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (g), and m is an integer from 1 to 5, a group of formula Het--CO--, whereHet represents a heterocyclic group having 5 to 6 ring atoms, of which from 1 to 3 are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted or having at least one substituent selected from the group consisting of C1 -C5 alkyl groups, a C1 -C5 alkyl group, a C1 -C5 alkyl group substituted by a group of formula --COOR8a, whereR8a represents a hydrogen atom, a C1 -C5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C1 -C5, a C2 -C5 hydroxyalkyl group, a C2 -C5 alkyl group substituted by a group of formula --O--CO--R53, whereR53 represents a C1 -C10 alkyl group, a phenyl group, a phenyl group having at least one substituent selected from the group consisting of substituents (g) or a heterocyclic group Het, as defined above, or a C1 -C3 alkyl group substituted by a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (g) are selected from the group consisting of C1 -C5 alkyl groups, trifluoromethyl groups, C1 -C5 alkoxy groups, halogen atoms, nitro groups, amino groups, hydroxy groups and dialkylamino groups where each alkyl part is C1 -C5 ; said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C1 -C4, dialkylcarbamoyl groups where each alkyl part is C1 -C4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; R4 represents a C1 -C10 alkyl group or a methoxy group; R5 represents a hydrogen atom, a C1 -C5 alkyl group or a methoxy group; R6 and R7 are independently selected from the group consisting of hydrogen atoms, C1 -C5 alkyl groups, C1 -C5 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined above, C2 -C5 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a group of formula --O--CO--R53 where R53 is as defined above, and C1 -C3 alkyl groups having a single substituent selected from the group consisting of substituents (h); Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH2)n --O-- at its 2-position and is attached to the --CH2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a C1 -C3 alkyl substituent; W represents a group of formula --CH2 --, >C═O, >CH--OR11 or >C═N--OR12 whereR11 represents a hydrogen atom, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C6 -C10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R13 --(CH2)m --CO-- where R13 and m are as defined above or a group of formula Het--CO-- where Het is as defined above, and R12 represents a hydrogen atom, a C1 -C5 alkyl group, a C1 -C10 alkyl group having at least one substituent selected from the group consisting of substituents (j), a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C6 -C10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), or said group of formula R13 --(CH2)m --CO-- or Het--CO--; and said substituents (j) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (g), C2 -C11 alkanoyloxy groups, C2 -C11 alkanoyloxy groups substituted by a group of formula --COOR8a where R8a is as defined above, C3 -C11 alkenoyloxy groups substituted by a group of formula --COOR8a where R8a is as defined above, phenylalkenoyloxy groups where the alkenyl part is C2 -C10 and the phenyl part is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (g), groups of formula --COOR8a where R8a is as defined above, benzyloxycarbonyl groups and groups of formula --COR9 R10 where R9 and R10 are as defined above; U represents(i) where W represents a group of formula --CH2 --, >C═O, >CH2 OR11 or >C═N--OR12, a group of formula --CH2 --, (ii) with W, a group of formula --CH═CH--, or (iii) where W represents a group of formula >C═O or >C═N--OR14, in which R14 represents any one of the acyl groups defined for R12, with R1 and the carbon atom to which R1 is attached, a group of formula --CH═C<. 24. A composition as claimed in claim 23, in which:R1, R2, R4, R5, Ar, W and U are as defined in claim 23; R6 and R7 both represent hydrogen atoms; R3 and R11 are independently selected from the group consisting of hydrogen atoms, C1 -C10 alkanoyl groups, C3 -C10 alkenoyl groups, C1 -C10 alkanoyl or C3 -C10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 23, arylcarbonyl groups as defined in claim 23, and groups of formulae R13 --(CH2)m --CO-- and Het--CO-- where R13, m and Het are as defined in claim 23; and R12 represents any one of the groups or atoms defined for R3 and R11 or a C1 -C5 alkyl group or a C1 -C3 alkyl group having at least one substituent selected from the group consisting of substituents (f) defined in claim 23. 25. A composition as claimed in claim 23, in which:R1, R2, R4, R5, Ar, W and U are as defined in claim 23; R3, R6, R7 and R12 are independently selected from the group consisting of hydrogen atom, C1 -C5 alkyl groups, C1 -C5 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 23, C2 -C5 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a group of formula --O--CO--R53 where R53 is as defined in claim 23 and C1 -C3 alkyl groups substituted by a single substituent selected from the group consisting of substituents (h) as defined in claim 23; and R11 represents a hydrogen atom, an acetyl group or a benzoyl group; R12 represents a hydrogen atom, a C1 -C5 alkyl group, a C1 -C10 alkly group having at least one substituent selected from the group consisting of substituents (k), a C2 -C6 alkanoyl group, a C2 -C10 alkanoyl group having at least one substituent selected from the group consisting of substituents (l), a C3 -C5 alkenoyl group, a C3 -C5 alkenoyl group having at least one substituent selected from the group consisting of substituents (l), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (m), a pyridinecarbonyl group, a furoyl group, a thenoyl group or a pyridinecarbonyl, furoyl or thenoyl group having at least one substituent selected from the group consisting of C1 -C5 alkyl groups; said substituents (k) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (m), C2 -C5 alkanoyloxy groups, C2 -C10 alkanoyloxy or C3 -C10 alkenoyloxy groups substituted by a group of formula --COOR8a where R8a is as defined in claim 23, C3 -C10 alkenoyloxy groups substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (m), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (m), groups of formula --COOR8a where R8a is as defined in claim 23 and substituents (h) as defined in claim 23; said substituents (l) are selected from the group consisting of phenyl groups, carboxy groups, alkoxycarbonyl groups where the alkoxy part is C1 -C5 and benzyloxycarbonyl groups; and said substituents (m) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups, halogen atoms and trifluoromethyl groups. 26. A composition as claimed in claim 22, in which:R1 represents an alkyl group selected from the group consisting of methyl, ethyl, isobutyl, pentyl, hexyl, 3,3-dimethylbutyl, heptyl, 4,4-dimethylpentyl, octyl, 5,5-dimethylhexyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a substituted C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (n), an aralkanoyl group of formula R15 --(CH2)m --CO--where R15 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (n), and m is an integer from 1 to 5, a pyridinecarbonyl group, a furoyl group, a thenoyl group, a C1 -C3 alkyl group, a C1 -C3 alkyl group substituted by a group of formula --COOR8a whereR8a represents a hydrogen atom, a C1 -C5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C1 -C5, a C2 -C3 hydroxyalkyl group, a C1 -C5 alkyl group substituted by a C1 -C5 alkoxy group, a C2 -C5 alkyl group substituted by a C2 -C4 alkanoyloxy or a benzoyloxy group or a methyl group having a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (n) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and halogen atoms; R4 represents a C1 -C10 alkyl group; R5 represents a hydrogen atom or a C1 -C3 alkyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms, C1 -C3 alkyl groups, C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined above, C2 -C3 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a C2 -C4 alkanoyloxy or a benzoyloxy group, and methyl groups substituted by a single substituent selected from the group consisting of substituents (h); said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C1 -C4, dialkylcarbamoyl groups where each alkyl part is C1 -C4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH2)n --O-- at its 2-position and is attached to the --CH2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a methyl substituent; W represents a group of formula --CH2 --, >C═O, >CH--OR11 or >C═N--OR12, where:R11 represents a hydrogen atom or any one of the acyl groups defined above for R3 ; and R12 represents a benzyl group, any one of the groups or atoms defined above for R3, a pyridinecarbonyl group or a pyridinecarbonyl group having at least one substituent selected from the group consisting of C1 -C5 alkyl groups; and U represents(i) where W represents a group of formula --CH2 --, >C═O, >CH--OR11 or >C═N--OR12, a group of formula --CH2 --, (ii) with W, a group of formula --CH═CH--, or (iii) where W represents a group of formula >C═O, with R1 and the carbon atom to which R1 is attached, a group of formula --CH═C<. 27. A composition as claimed in claim 26, in which:R1, R2, R4, R5, Ar, W and U are as defined in claim 26; R6 and R7 are both hydrogen atoms; R3 and R11 are independently selected from the group consisting of hydrogen atoms, C1 -C10 alkanoyl groups, C3 -C10 alkenoyl groups, C1 -C10 alkanoyl or C3 -C10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 26, benzoyl groups, benzoyl groups having at least one substituent selected from the group consisting of substituents (n) as defined in claim 26, groups of formula R15 --(CH2)m --CO-- where R15 and m are as defined in claim 26, pyridinecarbonyl groups, furoyl groups and thenoyl groups; and R12 represents a hydrogen atom, a methyl group, a benzyl group, a t-butoxycarbonylmethyl group or any one of the acyl groups defined above for R3 and R11. 28. A composition as claimed in claim 26, in which:R1, R2, R4, R5, Ar, W and U are as defined in claim 26; R3, R6 and R7 are independently selected from the group consisting of C1 -C3 alkyl groups, C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 26, C2 -C3 hydroxyalkyl groups, C1 -C5 alkyl groups substituted by a C1 -C5 alkoxy group, C2 -C5 alkyl groups substituted by a C2 -C4 alkanoyloxy or a benzoyloxy group, and methyl groups having a single substituent selected from the group consisting of substituents (h) as defined in claim 26; R11 represents a hydrogen atom; R12 represents a hydrogen atom, a C1 -C3 alkyl group having at least one substituent selected from the group consisting of substituents (o), a C2 -C4 alkanoyl group, a C2 -C4 alkanoyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 26, an acryloyl group, an acryloyl group having a β-substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (q), a pyridinecarbonyl group, a pyridinecarbonyl group having at least one substituent selected from the group consisting of C1 -C5 alkyl groups or any one of the groups defined above for R3, R6 and R7 ; said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C2 -C6 alkoxycarbonyl groups and benzyloxycarbonyl groups; and said substituents (o) are selected from the group consisting of carboxy groups and alkoxycarbonyl groups where the alkoxy part is C1 -C5 ; said substituents (g) are selected from the group consisting of methyl groups, ethyl groups, methoxy groups and ethoxy groups. 29. A composition as claimed in claim 22 in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO--where R16 represents a hydrogen atom or a C1 -C5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R17 OOC.CH═CH--CO--where R17 represents a hydrogen atom, a C1 -C5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a whereR8a represents a hydrogen atom, a C1 -C5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C1 -C5 ; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms and C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined above; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O, >C═N--OH, >C═N--OCH2 COOH or >C═N--OCOR18 where R18 represents a C1 -C5 alkyl group; and U represents a group of formula --CH2 --. 30. A composition as claimed in claim 29, in which:R1, R2, R4, R5, Ar and U are as defined in claim 29; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, a C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO-- where R16 and m are as defined in claim 29, a cis or trans- group of formula R17 OOC.CH═CH--CO-- where R17 is as defined in claim 29, or a 2-, 3- or 4-pyridinecarbonyl group; R6 and R7 are both hydrogen atoms; W represents a group of formula >C═NOR12 whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 29, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R3, R6 and R7 ; and n is 1 or 2. 31. A composition as claimed in claim 29, in which:R1, R2, R4, R5, Ar and U are as defined in claim 29; R3, R6 and R7 are independently selected from the group consisting of C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 29; W represents a group of formula >CH2, >C═O or >C═NOR12 ; R12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 29, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R3, R6 and R7 ; and n is 1 or 2. 32. A composition as claimed in claim 23, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C10 alkanoyl group, a C3 -C10 alkenoyl group, a C1 -C10 alkanoyl or C3 -C10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f) as defined in claim 23, an arylcarbonyl group as defined in claim 23, a group of formula R13 --(CH2)m --CO-- of Het--CO-- where R13, m and Het are as defined in claim 23 or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 23; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 represents a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 23; R7 represents a hydrogen atom or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 23; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula >CH2, >C═O or >C═NOR12, whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 23, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 23; U represents a group of formula --CH2 --; and n is 1 or 2. 33. A composition as claimed in claim 23, in which:R1 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO--where R16 represents a hydrogen atom or a C1 -C5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R17 OOC.CH═CH--CO--where R17 represents a hydrogen atom, C1 -C5 alkyl group of a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 23; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms and C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 23; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O or >C═N--OR12, whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 23, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C1 -C5 alkyl group, a C1 -C5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R3, R6 and R7 ; said substituents (n) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and halogen atoms; and U represents a group of formula --CH2 --. 34. A composition as claimed in claim 23, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents a hydrogen atom, a C1 -C5 alkanoyl group, C3 -C5 alkenoyl group, a cinnamoyl group, a group of formula R16 OOC(CH2)m CO--where R16 represents a hydrogen atom or a C1 -C5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R17 OOC.CH═CH--CO--where R17 represents a hydrogen atom, a C1 -C5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C1 -C3 alkyl group substituted by a group of formula --COOR8a where R8a is as defined in claim 23; R4 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are independently selected from the group consisting of hydrogen atoms and C1 -C3 alkyl groups substituted by a group of formula --COOR8a where R8a is as defined in claim 23; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O or >C═N--OR12 whereR12 represents a hydrogen atom, a group of formula --(CH2)3 COOR8a, --CH2 COOR8a, --C(CH3)2 COOR8a, --COCH2 CH2 COOR8a or --CO--CH═CH--COOR8a where R8a is as defined in claim 23, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C1 -C5 alkyl group, a C1 -C5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R3, R6 and R7 ; said substituents (n) are selected from the group consisting of C1 -C5 alkyl groups, C1 -C5 alkoxy groups and halogen atoms; and U represents a group of formula --CH2 --. 35. A composition as claimed in claim 23, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents C1 -C3 alkyl group substituted by a group of formula --COOR8a, where R8a is as defined in claim 23; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O, >C═N--OH, or >C═N--O--(C1 -C3 alkyl)--COOR8a where R8a is as defined in claim 23; U represents a group of formula --CH2 --; and N is 1 to 2. 36. A composition as claimed in claim 23, in which:R1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R2 represents a hydrogen atom or a methyl group; R3 represents --CH2 --COO(C1 -C5 alkyl) group; R4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R5 represents a hydrogen atom or a methyl group; R6 and R7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH2)n --O-- or a pyridine-diyl group attached to said group of formula --(CH2)n --O-- at the 2-position and to the --CH2 -thiazolidine group at the 5-position; W represents a group of formula --CH2 --, >C═O, >C═N--OH, or >C═N--O--(C1 -C3 alkyl)--COO(C1 -C5 alkyl); U represents a group of formula --CH2 --; and n is 1 to 2. 37. A composition as claimed in claim 22, wherein said active compound is selected from the group consisting of:5-[4-(6-Hydroxy-5,7,8-trimethyl-2-octylchroman-2-ylmethoxy)benzyl]thiazolidine-2,4-dione; 5-{4-[6-Hydroxy-4-(E)-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy]benzyl}thiazolidine-2,4-dione; 5-{4-[6-Acetoxy-4-(E)-acetoxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy]benzyl}thiazolidine-2,4-dione; α-{5-[4-(6-Carboxymethoxy-2,5,7,8-tetramethyl-4-oxochroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid; α-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid; α,α'-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidine-3,5-diyl}diacetic acid; and pharmaceutically acceptable salts thereof.