R. FAGGIANI, H. E. HOWARD-LOCK, C. J. L. LOCK, and R. ORGIAS. Can. J. Chem. 69, 1 (1991).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, P212121, with cell dimensions a = 9.507(5), b = 19.185(5), c = 7.766(2) a and Z = 4. The structure was solved by standard methods and refined to R = 0.088, R,, = 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 NMR, vibrational, and electronic spectra are also discussed. On a CtudiC la reaction des D-et L-~Cnicillamines avec le chlorhydrate du pyridoxal et on a examink la nature des produits obtenu: par diffraction des rayons-X par un cristal unique. On a dtterminC la structure du composC A mentionnC dans le titre et form6 par la rtaction de la D-ptnicillamine avec le pyridoxal. Les cristaux sont orthorhombiques, P212121, avec a = 9,507(5), identiques, mais de chiralitts oppostes; c'est-a-dire que la D-pCnicillamine conduit au diastCrCoisomkre 2R,4S alors que la L-~Cnicillamine conduit au diasttrCoisomkre 2S,4R (sans contamination par les composantes S,S ou R,R). Toutefois, en solution, les spectres RMN montrent qu'il existe deux paires de diastCrCoisomkres (2R,4S et 2S,4S; 2S,4R et 2R,4R). I1 semble que, en solutions neutres ou alcalines, il se produit une tpimkrisation rapide de I'atome de carbone de la thiazolidine qui est attache a la portion pyridoxal. On discute aussi des caracttristiques spectrales (masse, RMN du 'H, vibrationnels et Clectroniques) de ces produits.