Stereospecific reactions of copper(II) complexes of serine and threonine with formaldehyde

Summary 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:bisL-(oxazolidine-4-carboxylato)]-copper(II) monohydrate (1) andbisL-(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 compexes 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 Vversus 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.