Coordination and reactivity of benzyloxycarbonyl-Ala(CN)-OR (R=H, CH3) in complexes of platinum(II)

The conversion of a nitrile to an oxazoline group in an amino acid side chain promoted by platinum(II) was investigated. While benzyloxycarbonyl-beta-cyano-alanine (Z-Ala(CN)-OH) did not give any evidence of coordination of the nitrile group to Pt(II) in different complexes, the corresponding methyl ester Z-Ala(CN)-OCH3 readily afforded the Pt(II)-nitrile complex trans-[Pt(CF3){Z-Ala(CN)-OCH3} (PPh(3))(2)][BF4] in good yield by reaction with the cationic derivative trans-[Pt(CF3)(PPh(3))(2)(solv)][BF4] (solv = CH2Cl2). The reactivity of the CN group in the complex trans-[Pt(CF3){Z-Ala(CN)OCH3}(PPh(3))(2)][BF4] with ClCH2CH2O- to form the oxazoline ligand 2 was examined. The presence of the oxazoline ring in the final products was evidenced by IR, H-1 and C-13 NMR data and confirmed by FAB and MALDI mass spectra, but its isolation was hampered by the cleavage of the oxazoline ring under the chromatographic conditions applied.