A racemate diastereoisomer and optical isomer of a compound of formula (I): ##STR00001## wherein B is H, a C.sub.6 or C.sub.10 aryl, C.sub.7-16 aralkyl; Het or (lower alkyl)-Het, all of which may be optionally substituted with C.sub.1-6 alkyl; C.sub.1-6 alkoxy; C.sub.1-6 alkanoyl; hydroxy; hydroxyalkyl; halo; haloalkyl; nitro; cyano; cyanoalkyl; amino optionally substituted with C.sub.1-6 alkyl; amido; or (lower alkyl)amide; or B is an acyl derivative of formula R.sub.4--C(O)--; a carboxyl derivative of formula R.sub.4--O--C(O)--; an amide derivative of formula R.sub.4--N(R.sub.5)--C(O)--; a thioamide derivative of formula R.sub.4--N(R.sub.5)--C(S)--; or a sulfonyl of formula R.sub.4--SO.sub.2; R.sub.5 is H or C.sub.1-6 alkyl; and Y is H or C.sub.1-6 alkyl; R.sup.3 is C.sub.1-8 alkyl, C.sub.3-7 cycloalkyl, or C.sub.4-10 alkylcycloalkyl, all optionally substituted with hydroxy, C.sub.1-6 alkoxy, C.sub.1-6 thioalkyl, amido, (lower alkyl)amido, C.sub.6 or C.sub.10 aryl, or C.sub.7-16 aralkyl; R.sub.2 is C.sub.2--R.sub.20, NH--R.sub.20, O--R.sub.20 or S--R.sub.20, wherein R.sub.20 is a saturated or unsaturated C.sub.3-7 cycloalkyl or C.sub.4-10 (alkylcycloalkyl), all of which being optionally mono-, di- or tri-substituted with R.sub.21, or R.sub.20 is a C.sub.6 or C.sub.10 aryl or C.sub.7-14 aralkyl optionally substituted, or R.sub.20 is Het or (lower alkyl)-Het, both optionally substituted, Het or (lower alkyl)-Het; carboxyl; carboxy(lower alkyl); C.sub.6 or C10 aryl, C.sub.7-14 aralkyl or Het, said aryl, aralkyl or Het being optionally substituted; and R.sup.1 is H; C.sub.1-6 alkyl, C.sub.3-7 cycloalkyl, C.sub.2-6 alkenyl, or C.sub.2-6 alkynyl, all optionally substituted with halogen; or a pharmaceutically acceptable salt or ester thereof.