Structural Studies of Derivatives of Thiazolidine-4-Carboxylic Acid

Abstract

<p> A series of derivatives of thiazolidine-4-carboxylic acid was prepared from two sulfur containing aminoacids, cysteine and D-penicillamine. Cysteine is very easily oxidized to a disulfide, while penicillamine is less susceptible to oxidation of the sulfhydryl group because of greater steric hindrance. Sulfhydryl aminoacids react readily with aldehydes and ketones to give thiazolidine rings with varying degrees of substitution.</p> <p> Many of the compounds prepared were studied in solution and in the solid state by means of nmr, vibrational spectroscopy, mass spectra and X-ray crystallographic data. Thiazolidine-4-carboxylic acids contain a free carboxyl group and a secondary amino group, both of which can be ionized. Infrared spectra and X-ray crystallography are useful in detecting ionization and hydrogen bonds. An example is given of a compound that can exist in both the zwitterion and the non ionized state depending on the solvent of recrystallization.</p> <p> From previous work in our group we were predicting that increasing steric crowding in the thiazolidine ring in close proximity to the ionizable groups would decrease the tendency of these molecules to ionize. No such simple relationship could be found.</p>