Details for Patent: 5,830,897

Title:	.alpha.- and .beta.-amino acid hydroxyethylamino sulfonamides useful as retroviral protease inhibitors
Abstract:	.alpha.- and .beta.-amino acid hydroxyethylamino sulfonamide compounds are effective as retroviral protease inhibitors, and in particular as inhibitors of HIV protease.
Inventor(s):	Vazquez; Michael L. (Gurnee, IL), Mueller; Richard A. (Glencoe, IL), Talley; John J. (St. Louis, MO), Getman; Daniel (Chesterfield, MO), DeCrescenzo; Gary A. (St. Peters, MO), Freskos; John N. (Clayton, MO)
Assignee:	G. D. Searle & Co. (Chicago, IL) Monsanto Company (St. Louis, MO)
Filing Date:	Jun 07, 1995
Application Number:	08/473,698
Claims:	1. Compound represented by the formula: ##STR361## or a pharmaceutically acceptable salt or ester thereof, wherein R represents hydrogen, alkoxycarbonyl, aralkoxycarbonyl, alkylcarbonyl, cycloalkylcarbonyl, cycloalkylalkoxycarbonyl, cycloalkylalkanoyl, alkanoyl, aralkanoyl, aroyl, aryloxycarbonyl, aryloxycarbonylalkyl, aryloxyalkanoyl, heterocyclylcarbonyl, heterocyclyloxycarbonyl, heterocyclylalkanoyl, heterocyclylalkoxycarbonyl, heteroaralkanoyl, heteroaralkoxycarbonyl, heteroaryloxy-carbonyl, heteroaroyl, alkyl, alkenyl, cycloalkyl, aryl, aralkyl, aryloxyalkyl, heteroaryloxyalkyl, hydroxyalkyl, aminocarbonyl, aminoalkanoyl, and mono- and disubstituted aminocarbonyl and mono- and disubstituted aminoalkanoyl groups, wherein the substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, heterocycloalkyalkyl groups, or where said aminoalkanoyl group is disubstituted, said substituents along with the nitrogen atom to which they are attached form a heterocycloalkyl or heteroaryl group; R' represents hydrogen and groups as defined for R.sup.3 or R and R' together with the nitrogen to which they are attached represent heterocycloalkyl and heteroaryl group; R.sup.1 represents hydrogen, --CH.sub.2 SO.sub.2 NH.sub.2, --CH.sub.2 CO.sub.2 CH.sub.3, --CO.sub.2 CH.sub.3, --CONH.sub.2, --CH.sub.2 C(O)NHCH.sub.3, --C(CH.sub.3).sub.2 (SH), --C(CH.sub.3).sub.2 (SCH.sub.3)--C(CH.sub.3).sub.2 (S{O}CH.sub.3), --C(CH.sub.3).sub.2 (S{O}.sub.2 CH.sub.3), alkyl, haloalkyl, alkenyl, alkynyl and cycloalkyl groups, and amino acid side chains selected from asparagine, S-methyl cysteine and the sulfoxide and sulfone thereof, isoleucine, allo-isoleucine, alanine, leucine, tert-leucine, phenylalanine, ornithine, histidine, norleucine, glutamine, threonine, glycine, allo-threonine, serine, aspartic acid, beta-cyano alanine and valine side chains; R.sup.2 represents alkyl, aryl, cycloalkyl, cycloalkylalkyl and aralkyl groups, which groups are optionally substituted with a group selected from alkyl and halogen groups, --NO.sub.2, --C.tbd.N, CF.sub.3, --OR.sup.9, and --SR.sup.9, wherein R.sup.9 represents hydrogen and alkyl groups; R.sup.3 represents hydrogen, alkyl, haloalkyl, alkenyl, alkynyl, hydroxyalkyl, alkoxyalkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heteroaryl, heterocycloalkylalkyl, aryl, aralkyl, heteroaralkyl, aminoalkyl and mono- and disubstituted aminoalkyl groups, wherein said substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, and heterocycloalkylalkyl groups, or in the case of a disubstituted aminoalkyl group, said substituents along with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl group, and; R.sup.4 represents groups as defined by R.sup.3 and wherein alkyl, alone or in combination, is a straight-chain or branched-chain hydrocarbon group having from 1 to 8 carbon atoms, alkenyl, alone or in combination, means a straight-chain or branched-chain hydrocarbon group having one or more double bonds and from 2 to 8 carbon atoms; alkynyl, alone or in combination, means a straight-chain hydrocarbon having one or more triple bonds and from 2 to 10 carbon atoms; cycloalkyl, alone or in combination, is a hydrocarbon ring containing from 3 to 8 carbon atoms; aryl, alone or in combination, means a phenyl or naphthyl group optionally substituted with alkyl, alkoxy, halogen, hydroxy, amino, nitro, cyano or haloalkyl groups, heterocyclyl or heterocycloalkyl means a saturated or partially unsaturated monocyclic, bicyclic or tricyclic heterocycle having one or more nitrogen, oxygen or sulphur heteroatoms, which is optionally substituted on one or more carbon atoms by halogen, alkyl, alkoxy, or oxo groups, or on a secondary nitrogen atom by alkyl, aralkoxycarbonyl, alkanoyl, phenyl or phenylalkyl groups, or on a tertiary nitrogen atom by oxido group; and heteroaryl means an aromatic heterocyclyl group which is optionally substituted as defined above with respect to the definition of heterocyclyl. 2. Compound of claim 1 wherein R.sup.1 represents a methyl group. 3. Compound of claim 1 wherein R.sup.1 represents hydrogen, alkyl and alkenyl groups. 4. Compound of claim 1 wherein R.sup.1 represents alkyl groups having from 1 to about 4 carbon atoms and alkynyl groups having from 3 to 8 carbon atoms. 5. Compound of claim 1 wherein R.sup.1 represents methyl, ethyl, isopropyl, propargyl and t-butyl groups. 6. Compound of claim 1 wherein R' is hydrogen and R is ##STR362## 7. Compound of claim 1 wherein R' is hydrogen and R represents acetyl, phenoxyacetyl, 2-naphthyloxy-carbonyl, benzyloxycarbonyl, p-methoxybenzyloxycarbonyl. 8. Compound of claim 1 wherein R' is hydrogen and R is an aralkoxycarbonyl group. 9. Compound of claim 1 wherein R' is hydrogen and R represents heteroaralkoxycarbonyl group. 10. Compound of claim 1 wherein R and R' are independently selected from methyl and phenethyl groups. 11. Compound of claim 1 wherein R.sup.2 represents alkyl, cycloalkylalkyl and aralkyl groups, which groups are optionally substituted with halogen groups and groups represented by the formula --OR.sup.9 and --SR.sup.9 wherein R.sup.9 represents hydrogen and alkyl groups. 12. Compound of claim 1 wherein R.sup.2 represents alkyl, cycloalkylalkyl and aralkyl groups. 13. Compound of claim 1 wherein R.sup.2 represents aralkyl groups. 14. Compound of claim 1 wherein R.sup.2 represents CH.sub.3 SCH.sub.2 CH.sub.2 --, iso-butyl, n-butyl, benzyl, 4-fluorobenzyl, 2-naphthylmethyl and cyclohexylmethyl groups. 15. Compound of claim 1 wherein R.sup.2 represents an n-butyl and iso-butyl groups. 16. Compound of claim 1 wherein R.sup.2 represents benzyl, 4-fluorobenzyl, and 2-naphthylmethyl groups. 17. Compound of claim 1 wherein R.sup.2 represents a cyclohexylmethyl group. 18. Compound of claim 1 wherein R.sup.3 and R.sup.4 independently represent alkyl, haloalkyl, alkenyl, alkoxyalkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heterocycloalkylalkyl, heteroaryl, aryl, aralkyl and heteroaralkyl groups. 19. Compound of claim 18 wherein R.sup.4 represents methyl and phenyl. 20. Compound of claim 18 wherein R.sup.3 and R.sup.4 independently represent alkyl and alkenyl groups. 21. Compound of claim 18 wherein R.sup.3 and R.sup.4 independently represent alkyl and hydroxyalkyl groups. 22. Compound of claim 18 wherein R.sup.3 and R.sup.4 independently represent alkyl, cycloalkyl and cycloalkylalkyl groups. 23. Compound of claim 18 wherein R.sup.3 and R.sup.4 independently represent alkyl, heterocycloalkyl and heterocycloalkylalkyl groups. 24. Compound of claim 18 wherein R.sup.3 and R.sup.4 independently represent alkyl, heteroaryl, aryl and aralkyl groups. 25. Compound of claim 18 wherein R.sup.3 and R.sup.4 independently represent alkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heterocycloalkylalkyl, heteroaryl, aryl, aralkyl, and heteroaralkyl groups. 26. Compound of claim 1 wherein R.sup.3 represents alkyl groups having from about 2 to about 5 carbon atoms. 27. Compound of claim 26 wherein R.sup.4 represents methyl, phenyl and substituted phenyl groups. 28. Compound of claim 1 wherein R.sup.3 and R.sup.4 independently represent alkyl groups having from about 2 to about 5 carbon atoms, cycloalkylalkyl groups, aryl groups, aralkyl groups, heterocycloalkylalkyl groups and heteroaralkyl groups. 29. Compound of claim 1 wherein R.sup.3 represents isobutyl, n-propyl, n-butyl, isoamyl, cyclohexylmethyl, cyclohexyl, benzyl, para-fluorobenzyl, para-methoxybenzyl, para-methylbenzyl and 2-naphthylmethyl groups and R.sup.4 represents phenyl and substituted phenyl groups wherein substituents of the substituted phenyl radical are selected from chloro fluoro, nitro, methoxy and amino substituents. 30. Compound of claim 1 wherein R.sup.3 is cyclohexylmethyl and R.sup.4 phenyl. 31. Compound of claim 1 wherein R.sup.3 is i-amyl and R.sup.4 is phenyl. 32. Compound of claim 1 wherein R.sup.3 is i-butyl and R.sup.4 is phenyl. 33. Compound of claim 1 wherein R.sup.3 is n-butyl and R.sup.4 is phenyl. 34. Compound of claim 1 wherein R.sup.3 is cyclohexyl and R.sup.4 is phenyl. 35. Compound of claim 1 wherein R.sup.4 represents alkyl and cycloalkyl groups. 36. Compound of claim 1 wherein R.sup.4 represents methyl and cyclohexyl groups. 37. Compound of claim 1 wherein R and R' together with the nitrogen to which they are bonded represent pyrrolidinyl, piperidinyl, morpholinyl, and piperazinyl groups. 38. Compound of claim 1 wherein R.sup.3 represents heteroaralkyl groups and R.sup.4 is methyl or phenyl. 39. Compound of claim 1 wherein R.sup.3 is a p-fluorobenzyl group and R.sup.4 is a methyl or phenyl group. 40. A pharmaceutical composition comprising a compound of claim 1 and a pharmaceutically acceptable carrier. 41. Method of inhibiting a retroviral protease comprising administering a protease inhibiting amount of a composition of claim 40. 42. Method of claim 41 wherein the retroviral protease is HIV protease. 43. Method of treating a retroviral infection comprising administering an effective amount of a composition of claim 40. 44. Method of claim 43 wherein the retroviral infection is an HIV infection. 45. Method for treating AIDS comprising administering an effective amount of a composition of claim 40. 46. Compound represented by the formula: ##STR363## or a pharmaceutically acceptable salt or ester thereof, wherein R represents hydrogen, alkoxycarbonyl, aralkoxycarbonyl, alkylcarbonyl, cycloalkylcarbonyl, cycloalkylalkoxycarbonyl, cycloalkylalkanoyl, alkanoyl, aralkanoyl, aroyl, aryloxycarbonyl, aryloxycarbonylalkyl, aryloxyalkanoyl, heterocyclylcarbonyl, heterocyclyloxycarbonyl, heterocyclylalkanoyl, heterocyclylalkoxycarbonyl, heteroaralkanoyl, heteroaralkoxycarbonyl, heteroaryloxy-carbonyl, heteroaroyl, alkyl, alkenyl, cycloalkyl, aryl, aralkyl, aryloxyalkyl, heteroaryloxyalkyl, hydroxyalkyl, aminocarbonyl, aminoalkanoyl, and mono- and disubstituted aminocarbonyl and mono- and disubstituted aminoalkanoyl groups, wherein the substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, heterocycloalkyalkyl groups, or where said aminoalkanoyl group is disubstituted, said substituents along with the nitrogen atom to which they are attached form a heterocycloalkyl or heteroaryl group; R' represents hydrogen and groups as defined for R.sup.3 or R and R' together with the nitrogen to which they are attached represent heterocycloalkyl and heteroaryl group; R.sup.1 represents hydrogen, --CH.sub.2 SO.sub.2 NH.sub.2, --CH.sub.2 CO.sub.2 CH.sub.3, --CO.sub.2 CH.sub.3, --CONH.sub.2, --CH.sub.2 C(O)NHCH.sub.3, --C(CH.sub.3).sub.2 (SH), --C(CH.sub.3).sub.2 (SCH.sub.3), --C(CH.sub.3).sub.2 (S{O}CH.sub.3), --C(CH.sub.3).sub.2 (S{O}.sub.2 CH.sub.3), alkyl, haloalkyl, alkenyl, alkynyl and cycloalkyl groups, and amino acid side chains selected from asparagine, S-methyl cysteine and the sulfoxide and sulfone thereof, isoleucine, allo-isoleucine, alanine, leucine, tert-leucine, phenylalanine, ornithine, histidine, norleucine, glutamine, threonine, glycine, allo-threonine, serine, aspartic acid, beta-cyano alanine and valine side chains; R.sup.2 represents alkyl, aryl, cycloalkyl, cycloalkylalkyl and aralkyl groups, which groups are optionally substituted with a group selected from alkyl and halogen groups, --NO.sub.2, --C.tbd.N, CF.sub.3, --OR.sup.9, and --SR.sup.9, wherein R.sup.9 represents hydrogen and alkyl groups; R.sup.3 represents hydrogen, alkyl, haloalkyl, alkenyl, alkynyl, hydroxyalkyl, alkoxyalkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heteroaryl, heterocycloalkylalkyl, aryl, aralkyl, heteroaralkyl, aminoalkyl and mono- and disubstituted aminoalkyl groups, wherein said substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, and heterocycloalkylalkyl groups, or in the case of a disubstituted aminoalkyl group, said substituents along with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl group, and; R.sup.4 represents groups as defined by R.sup.3 and wherein alkyl, alone or in combination, is a straight-chain or branched-chain hydrocarbon group having from 1 to 8 carbon atoms, alkenyl, alone or in combination, means a straight-chain or branched-chain hydrocarbon group having one or more double bonds and from 2 to 8 carbon atoms; alkynyl, alone or in combination, means a straight-chain hydrocarbon group having one or more triple bonds and from 2 to 10 carbon atoms; cycloalkyl, alone or in combination, is a hydrocarbon ring containing from 3 to 8 carbon atoms; aryl, alone or in combination, means a phenyl or naphthyl group optionally substituted with alkyl, alkoxy, halogen, hydroxy, amino, nitro, cyano or haloalkyl groups; heterocyclyl or heterocycloalkyl means a saturated or partially unsaturated monocyclic, bicyclic or tricyclic heterocycle having 5 to 13 ring members, which contains at least one nitrogen, oxygen or sulphur heteroatom which is optionally substituted on one or more carbon atoms by halogen alkyl, alkoxy or oxo, or on a secondary nitrogen atom by alkyl, aralkoxycarbonyl, alkanoyl, phenyl or phenylalkyl or on a tertiary nitrogen atom by oxido; and a heteroaryl means an aromatic monocyclic, bicyclic, or tricyclic heterocycloalkyl group having 5 to 13 ring members which is optionally substituted with one or more alkyl, alkoxy, halogen, hydroxy, amino nitro, cytano, haloalkyl, carboxy, alkoxycarbonyl, cycloalkyl, amido, alkylamino, dialkylamino, alkylamido or dialkylamido groups. 47. The compound of claim 46 wherein said heterocyclyl, heterocycloalkyl or heteroaryl is selected from optionally substituted pyrrolidinyl, piperidinyl, piperazinyl, morpholinyl, thiamorpholinyl, pyrrolyl, imidazolyls, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, furyl, thienyl, triazolyl, oxazolyl, thiazolyl, indolyls, quinolynyls, isoquinolinyls, tetrahydroquinolinyls, 1,2,3,4-tetrahydroisoquinolinyls, quinoxalinyl, .beta.-carbolinyl, 2-benzofurancarbonyl, and benzimidazolyls groups. 48. Compound represented by the formula: ##STR364## or a pharmaceutically acceptable salt or ester thereof, wherein R represents hydrogen, alkoxycarbonyl, aralkoxycarbonyl, alkylcarbonyl, cycloalkylcarbonyl, cycloalkylalkoxycarbonyl, cycloalkylalkanoyl, alkanoyl, aralkanoyl, aroyl, aryloxycarbonyl, aryloxycarbonylalkyl, aryloxyalkanoyl, heterocyclylcarbonyl, heterocyclyloxycarbonyl, heterocyclylalkanoyl, heterocyclylalkoxycarbonyl, heteroaralkanoyl, heteroaralkoxycarbonyl, heteroaryloxy-carbonyl, heteroaroyl, alkyl, alkenyl, cycloalkyl, aryl, aralkyl, aryloxyalkyl, heteroaryloxyalkyl, hydroxyalkyl, aminocarbonyl, aminoalkanoyl, and mono- and disubstituted aminocarbonyl and mono- and disubstituted aminoalkanoyl groups, wherein the substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, heterocycloalkyalkyl groups, or where said aminoalkanoyl group is disubstituted, said substituents along with the nitrogen atom to which they are attached form a heterocycloalkyl or heteroaryl group; R' represents hydrogen and groups as defined for R.sup.3 or R and R' together with the nitrogen to which they are attached represent heterocycloalkyl and heteroaryl group; R.sup.1 represents hydrogen, --CH.sub.2 SO.sub.2 NH.sub.2, --CH.sub.2 CO.sub.2 CH.sub.3, --CO.sub.2 CH.sub.3, --CONH.sub.2, --CH.sub.2 C(O)NHCH.sub.3, --C(CH.sub.3).sub.2 (SH), --C(CH.sub.3).sub.2 (SCH.sub.3) --C(CH.sub.3).sub.2 (S{O}CH.sub.3), --C(CH.sub.3).sub.2 (S{O}.sub.2 CH.sub.3), alkyl, haloalkyl, alkenyl, alkynyl and cycloalkyl groups, and amino acid side chains selected from asparagine, S-methyl cysteine and the sulfoxide and sulfone thereof, isoleucine, allo-isoleucine, alanine, leucine, tert-leucine, phenylalanine, ornithine, histidine, norleucine, glutamine, threonine, glycine, allo-threonine, serine, aspartic acid, beta-cyano alanine and valine side chains; R.sup.2 represents alkyl, aryl, cycloalkyl, cycloalkylalkyl and aralkyl groups, which groups are optionally substituted with a group selected from alkyl and halogen groups, --NO.sub.2, --C.tbd.N, CF.sub.3, -OR.sup.9, and --SR.sup.9, wherein R.sup.9 represents hydrogen and alkyl groups; R.sup.3 represents hydrogen, alkyl, haloalkyl, alkenyl, alkynyl, hydroxyalkyl, alkoxyalkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heteroaryl, heterocycloalkylalkyl, aryl, aralkyl, heteroaralkyl, aminoalkyl and mono- and disubstituted aminoalkyl groups, wherein said substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, and heterocycloalkylalkyl groups, or in the case of a disubstituted aminoalkyl group, said substituents along with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl group, and; R.sup.4 represents groups as defined by R.sup.3 and wherein alkyl, alone or in combination, is a straight-chain or branched-chain hydrocarbon group having from 1 to 8 carbon atoms, alkenyl, alone or in combination, means a straight-chain or branched-chain hydrocarbon group having one or more double bonds and from 2 to 8 carbon atoms; alkynyl, alone or in combination, means a straight-chain hydrocarbon having one or more triple bonds and from 2 to 10 carbon atoms; cycloalkyl, alone or in combination, is a hydrocarbon ring containing from 3 to 8 carbon atoms; aryl, alone or in combination, means a phenyl or naphthyl group optionally substituted with alkyl, alkoxy, halogen, hydroxy, amino, nitro, cyano or haloalkyl groups, heterocyclyl or heterocycloalkyl means a saturated or partially unsaturated monocyclic, bicyclic or tricyclic heterocycle having one or more nitrogen, oxygen or sulphur heteroatoms, which is optionally substituted on one or more carbon atoms by halogen, alkyl, alkoxy, or oxo groups, or on a secondary nitrogen atom by alkyl, aralkoxycarbonyl, alkanoyl, phenyl or phenylalkyl groups, or on a tertiary nitrogen atom by oxido group; and heteroaryl means an aromatic heterocyclyl group which is optionally substituted as defined above with respect to the definition of heterocyclyl. 49. Compound represented by the formula: ##STR365## or a pharmaceutically acceptable salt or ester thereof, wherein R represents hydrogen, alkoxycarbonyl, aralkoxycarbonyl, alkylcarbonyl, cycloalkylcarbonyl, cycloalkylalkoxycarbonyl, cycloalkylalkanoyl, alkanoyl, aralkanoyl, aroyl, aryloxycarbonyl, aryloxycarbonylalkyl, aryloxyalkanoyl, heterocyclylcarbonyl, heterocyclyloxycarbonyl, heterocyclylalkanoyl, heterocyclylalkoxycarbonyl, heteroaralkanoyl, heteroaralkoxycarbonyl, heteroaryloxy-carbonyl, heteroaroyl, alkyl, alkenyl, cycloalkyl, aryl, aralkyl, aryloxyalkyl, heteroaryloxyalkyl, hydroxyalkyl, aminocarbonyl, aminoalkanoyl, and mono- and disubstituted aminocarbonyl and mono- and disubstituted aminoalkanoyl groups, wherein the substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, heterocycloalkyalkyl groups, or where said aminoalkanoyl group is disubstituted, said substituents along with the nitrogen atom to which they are attached form a heterocycloalkyl or heteroaryl group; R' represents hydrogen and groups as defined for R.sup.3 or R and R' together with the nitrogen to which they are attached represent heterocycloalkyl and heteroaryl group; R.sup.1 represents hydrogen, --CH.sub.2 SO.sub.2 NH.sub.2, --CH.sub.2 CO.sub.2 CH.sub.3, --CO.sub.2 CH.sub.3, --CONH.sub.2, --CH.sub.2 C(O)NHCH.sub.3, --C(CH.sub.3).sub.2 (SH), --C(CH.sub.3).sub.2 (SCH.sub.3), --C(CH.sub.3).sub.2 (S[O]CH.sub.3), --C(CH.sub.3).sub.2 (S[O].sub.2 CH.sub.3), alkyl, haloalkyl, alkenyl, alkynyl and cycloalkyl groups, and amino acid side chains selected from asparagine, S-methyl cysteine and the sulfoxide and sulfone thereof, isoleucine, allo-isoleucine, alanine, leucine, tert-leucine, phenylalanine, ornithine, histidine, norleucine, glutamine, threonine, glycine, allo-threonine, serine, aspartic acid, beta-cyano alanine and valine side chains; R.sup.2 represents alkyl, aryl, cycloalkyl, cycloalkylalkyl and aralkyl groups, which groups are optionally substituted with a group selected from alkyl and halogen groups, --NO.sub.2, --C.tbd.N, CF.sub.3, --OR.sup.9, and --SR.sup.9, wherein R.sup.9 represents hydrogen and alkyl groups; R.sup.3 represents hydrogen, alkyl, haloalkyl, alkenyl, alkynyl, hydroxyalkyl, alkoxyalkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heteroaryl, heterocycloalkylalkyl, aryl, aralkyl, heteroaralkyl, aminoalkyl and mono- and disubstituted aminoalkyl groups, wherein said substituents are selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl, heteroaryl, heteroaralkyl, heterocycloalkyl, and heterocycloalkylalkyl groups, or in the case of a disubstituted aminoalkyl group, said substituents along with the nitrogen atom to which they are attached, form a heterocycloalkyl or a heteroaryl group, and; R.sup.4 represents groups as defined by R.sup.3 and wherein alkyl, alone or in combination, is a straight-chain or branched-chain hydrocarbon group having from 1 to 8 carbon atoms, alkenyl, alone or in combination, means a straight-chain or branched-chain hydrocarbon group having one or more double bonds and from 2 to 8 carbon atoms; alkynyl, alone or in combination, means a straight-chain hydrocarbon group having one or more triple bonds and from 2 to 10 carbon atoms; cycloalkyl, alone or in combination, is a hydrocarbon ring containing from 3 to 8 carbon atoms; aryl, alone or in combination, means a phenyl or naphthyl group optionally substituted with alkyl, alkoxy, halogen, hydroxy, amino, nitro, cyano or haloalkyl groups; heterocyclyl or heterocycloalkyl means a saturated or partially unsaturated monocyclic, bicyclic or tricyclic heterocycle having 5 to 13 ring members, which contains at least one nitrogen, oxygen or sulphur heteroatom which is optionally substituted on one or more carbon atoms by halogen alkyl, alkoxy or oxo, or on a secondary nitrogen atom by alkyl, aralkoxycarbonyl, alkanoyl, phenyl or phenylalkyl or on a tertiary nitrogen atom by oxido; and a heteroaryl means an aromatic monocyclic, bicyclic, or tricyclic heterocycloalkyl groups having 5 to 13 ring members which is optionally substituted with one or more alkyl, alkoxy, halogen, hydroxy, amino nitro, cytano, haloalkyl, carboxy, alkoxycarbonyl, cycloalkyl, amido, alkylamino, dialkylamino, alkylamido or dialkylamido groups.