Diorganotin(IV)-promoted deamination of amino acids by pyridoxal: SnR 2 2+ complexes of pyridoxal 5′-phosphate and of the Schiff base pyridoxal-pyridoxamine (PLPM), and antibacterial activities of PLPM and [SnR 2(PLPM-2H)] (R=Me, Et, Bu, Ph)

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Pyridoxal 5′-phosphate (PLP) and pyridoxal (PL) itself were reacted with diorganotin(IV) derivatives in the presence and absence of aminoacids. With PLP the complexes [SnR 2(PLP-2H)] (R=Me, Et, Bu) were isolated and characterized by EI and FAB mass spectrometry and by IR, Raman and Mössbauer spectroscopy. Reaction mixtures containing PL, valine or glycine and SnR 2(OAc) 2 (R=Me, Et) afforded complexes of the form [SnR 2(PLPM-2H)], where PLPM is the Schiff base formed by condensation of PL and pyridoxamine (PM). PM was presumably formed by transamination between valine or glycine and PL. The PLPM complexes, and their butyl and phenyl analogues, were also synthesized directly by reacting SnR 2O and PLPM, and were characterized by EI and FAB MS, by IR, Raman, Mössbauer and NMR spectroscopy, and in the case of the methyl and ethyl compounds by single-crystal X-ray diffractometry. Crystals of [SnMe 2(PLPM-2H)]·H 2O and [SnEt 2(PLPM-2H)] consist of molecules in which the ligand is bound to the metal through the O atoms of the two deprotonated phenolic hydroxyl groups and the iminic N atom, and the metal exhibits distorted square pyramidal coordination. Both PLPM and its complexes show intense antibacterial activity against Pseudomonas aeruginosa (ATCC27853), but only the complexes exhibit significant activity against the other four bacterial strains assayed, Staphylococcus aureus, Bacillus subtilis, Escherichia coli and a carbapenem-resistant P. aeruginosa strain.