STEREOSPECIFIC REACTIONS OF COPPER(II) COMPLEXES OF SERINE AND THREONINE WITH FORMALDEHYDE

Condensations of Cu(L-ser)2 and Cu(L-thr)2 (where L-ser = L-serinato anion and L-thr = L-threoninato anion) with formaldehyde at pH 4.5 yield two new optically active products: bis[L-(oxazolidine-4-carboxylato)]-copper(II) monohydrate (1) and bis[L-(N-hydroxymethyl-5-methyloxazolidine-4-carboxylato)]copper(II) dihydrate (2), respectively. Cu(D-ser)2 and Cu(D-thr)2 also undergo similar reactions. The new products are different from the products obtained from Cu(DL-ser)2 and Cu(DL-thr)2, and a mechanism has been suggested to explain the stereospecificity of these conversions. Condensation of Cu(L-ser)2 with formaldehyde and ammonia at pH 4.5 yields the new product, [3N,7N-(1,3,5,7-tetraazabicyclo-[3.3.1]nonyl)di(hydroxymethyl)-acetato]copper(II), (3). The complexes have been characterized by analytical and by i.r., electronic and c.d. spectral data. Complexes (1) and (2) undergo a reversible Cu(II)/Cu(I) redox process in aqueous media at -0.18 V versus s.c.e.; complex (3) exhibits irreversible Cu(II)/Cu(I) reduction at -0.49 V confirming the presence of a rigid pentamethylenediaza-bridged ligand system.