A methylenic group binds guanidinoacetic acid to glycine and serine in two novel copper(II) complexes: Synthesis,X-ray structure and spectroscopic characterization

New condensed amino acids were observed in two Cu(II) complexes, both involving guanidinoacetic acid (GAA). The copper(II) complexes, 1 and 2, were synthesized and characterized by X-ray crystallography and infrared spectroscopy. Vibrational assignments were performed with the aid of density functional theory (DFT) calculations. Both complexes present an elongation of the carbon chain of the starting amino acid, GAA. One methylenic group binds GAA to the other amino acid, which can be glycine or serine. Complex 1 presents a new condensed synthetic amino acid, glycine-3-N-methylguanidino acetic acid (Gly-mGAA) that is the result/product of the reaction between GAA and glycine, with an addition of one carbon in the chain. In complex 2, a similar ligand to Gly-mGAA was observed, but in this case it is a product of the reaction between GAA and serine, that is, serine-3-N-methylguanidino acetic acid (Ser-mGAA). Gly-mGAA and Ser-mGAA coordinate to Cu(II) through two nitrogen atoms and two oxygen atoms. In addition, we attempt to propose the mechanism for formation of Ser-mGAA and Gly-mGAA in two steps. The first one involves a deamidination reaction between two GAA species, producing the intermediate N,N′-guanidinodiacetic acid. The second step involves a decarboxylation process between GAA and Ser or Gly.