5-substituted alkylidene 2-(N-cyanoimino)-thiazolidin-4-one derivatives, their preparation and their use as aldose reductase inhibitors

A class of compounds represented by the formula (I) wherein R1s are the same or different groups and each represents hydrogen atom or alkyl group having 1 to 4 carbon atoms; R2 is phenyl group, naphthyl group, or either phenyl or naphthyl substituted with at least one hydroxyl, alkyl having 1 to 4 carbon atoms or alkoxy having 1 to 4 carbon atoms; R3 is hydrogen atom, alkyl group having 1 to 4 carbon atoms or CH2COOR4 group, in which R4 is hydrogen atom or alkyl group having 1 to 12 carbon atoms; n is 0 or 1, the configuration of 5-methylene group includes both E-isomer and Z-isomer, providing excepting the case wherein R1 is hydrogen atom, R2 is 3,5-di-t-butyl-4-hydroxyphenyl, R3 is hydrogen atom and n is 0 or pharmacologically acceptable salts thereof when R3 or R4 is hydrogen atom. The invention also concerns preparation methods thereof. The present compounds are useful as prophylactic or therapeutic agents for neuropathy, retinopathy, diabetic cataract, impediment in the kidney as tubulo-nephrosis, all known as complications of chronic diabetes and especially aldose reducing enzyme induced complications.