Racemates, diastereoisomers and optical isomers of a compound of formula (I): wherein B is H, a C6 or C10 aryl, C7-16 aralkyl; Het or (lower alkyl)-Het, all of which optionally substituted with C1-6 alkyl; C1-6 alkoxy; C1-6 alkanoyl; hydroxy; hydroxyalkyl; halo; haloalkyl; nitro; cyano; cyanoalkyl; amino optionally substituted with C1-6 alkyl; amido; or (lower alkyl)amide; or B is an acyl derivative of formula R4—C(O)—; a carboxyl of formula R4—O—C(O)—; an amide of formula R4—N(R5)—C(O)—; a thioamide of formula R4—N(R5)—C(S)—; or a sulfonyl of formula R4—SO2; R5 is H or C1-6 alkyl; and Y is H or C1-6 alkyl; R3 is C1-8 alkyl, C3-7 cycloalkyl, or C4-10 alkylcycloalkyl, all optionally substituted with hydroxy, C1-6 alkoxy, C1-6 thioalkyl, amido, (lower alkyl)amido, C6 or C10 aryl, or C7-16 aralkyl; R2 is CH2—R20, NH—R20, O—R20 or S—R20, wherein R20 is a saturated or unsaturated C3-7 cycloalkyl or C4-10 (alkylcycloalkyl), all of which being optionally mono-, di- or tri-substituted with R21, or R20 is a C6 or C10 aryl or C7-14 aralkyl optionally substituted, or R20 is Het or (lower alkyl)-Het, both optionally substituted, Het or (lower alkyl)-Het; carboxyl; carboxy(lower alkyl); C6 or C10 aryl, C7-14 aralkyl or Het, said aryl, aralkyl or Het being optionally substituted; and R1 is H; C1-6 alkyl, C3-7 cycloalkyl, C2-6 alkenyl, or C2-6 alkynyl, all optionally substituted with halogen; or a pharmaceutically acceptable salt or ester thereof.