Coordination modes of aminoacids to zinc

Abstract

Two new binary zinc–aminoacid complexes were crystallized: Zn(Ile) 2(H 2O) 2 is octahedral with two O,N-chelating aminoacid ligands; Zn(Phe) 2 is a one-dimensional coordination polymer with η 2-carboxylate bridges. The pyrazolylborate zinc complex Tp Ph,MeZnOH reacted with simple aminoacids to form the complexes Tp Ph,MeZn-AA (AA=Gly, Val, Leu, Met, Phe, Trp) in which AA is a O,N-chelate ligand. In a similar fashion aminoacid-nitroanilides were deprotonated at the N atom yielding the Tp Ph,MeZn complexes with the N,N-chelating ligands Gly-Nit, Ala-Nit and Leu-Nit. When terminal amino functions were missing, pure carboxylate coordination resulted, as in Tp Ph,MeZn-GlyPheBoc and Tp Ph,MeZn-AspPheOMe. Exclusive side-chain coordination was enforced in Bz-Tyr-OEt resulting in the Tp Ph,MeZn complex with the phenolate-bound aminoacid. Combinations of the binding types (O,N-chelate+carboxylate, O,N-chelate+phenolate, O,N-chelate+thiolate) were realized in the binuclear complexes Tp Ph,MeZn-AA-ZnTp Ph,Me for AA=Asp, Glu, Tyr and Cys.