2R,4S-2-(2'-METHYL-3'-HYDROXY-5'-HYDROXYMETHYLENEPYRIDINE-C4')-5,5-DIMETHYLTHIAZOLIDINE-4-CARBOXYLIC ACID, THE PRODUCT OF THE REACTION OF D-PENICILLAMINE AND VITAMIN-B6

We have studied the reaction of both D- and L-penicillamine with pyridoxal hydrochloride and examined the products by single crystal X-ray diffraction. The structure of the title compound, A, formed by the reaction of D-penicillamine and pyridoxal was determined. Crystals are orthorhombic, P2(1)2(1)2(1), with cell dimensions a = 9.507(5), b = 19.185(5), c = 7.766(2) angstrom and Z = 4. The structure was solved by standard methods and refined to R = 0.088, R(w) = 0.079 for 2433 independent reflections. A exists as a zwitterion, and bond lengths and angles are normal. In the solid state, A and the corresponding product obtained from L-penicillamine, B, have identical geometrical structure but are of opposite chirality; that is, D-penicillamine produces the 2R,4S diastereomer and L-penicillamine produces the 2S,4R diastereomer (with no S,S and R,R components). In solution, however, NMR spectra show the presence of both pairs of diastereomers (2R,4S and 2S,4S; 2S,4R and 2R,4R). In neutral or alkaline solution there appears to be a rapid epimerization at the thiazolidine carbon atom attached to the pyridoxal moiety. Features of the mass, H-1 NMR, vibrational, and electronic spectra are also discussed.