Synthesis and Aldose Reductase Inhibitory Activity of Thiazolidinecarboxylic Acids Containing a Disulfide Bond

Symmetrical disulfides (2a-m, 9, 13) were synthesized by oxidation or by a new reaction using ethyl α-bromomalonate from the corresponding thiazolidinecarboxylic acids containing a sulfhydryl group (1a-m, 8, 12). Mixed disulfides (14a-g) were synthesized by reaction of thiols (1a, c) with Bunte salt. Stereoselective acylation of the thiazolidinecarboxylic acid 5a gave the symmetrical disulfide 2c or the dicarboxylic acid 15, depending on the conditions. The absolute configurations of these disulfides were decided to be (2R, 2'R, 4R, 4'R) by comparison of nuclear magnetic resonance spectra and specific rotation with those of the (2S, 2'S, 4R, 4'R)-disulfide (4). The disulfides were tested for aldose reductase inhibitory activity in vitro. The symmetrical disulfide 2j and dicarboxylic acid 15 showed remarkably high potency.