A monocarboxylic acid that is 1,3-thiazolidine which is substituted on the nitrogen by a carboxymethyl group, at positions 2 and 4 by thioxo and oxo groups, respectively, and at position 5 by a 2-methyl-3-phenylprop-2-en-1-ylidene group. It is an inhibitor of aldose reductase (which catalyses the conversion of glucose to sorbitol) and is used for the treatment of some diabetic complications, including neuropathy.