Diastereoselective hydrogenation of complexes of acetyldehydrophenylalanylmethionine and its esters with PdCl2

A new method, on principle, for the diastereoselective hydrogenation of dehydrodipeptides (DHDPs) and their esters entailing the utilization of the complex of the DHDP with PdCl₂ as the substrate was proposed. The formation of a certain conformation of the DHDP chain produced by the central atom of the metal complex-former permits the asymmetric synthesis of N-acetylphenylalanylmethionine with the optical yield up to 40%. The optical yield of the product depends both on the configuration of the methionine part of the peptide and on the bulk of the ester group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2828–2832, December, 1989.     

Synthesis of 4,2′-iodonio-3-phenyl-1,2-benzisoxazole tetrafluoroboride and the crystal structure of its monohydrate

Conclusions 4,2-Iodonio-3-phenyl-l,2-benzisoxazole tetrafluoroboride monohydrate (IV) was synthesized and an x-ray diffraction structural study showed that the cation (IV) is a tetracyclic system and the crystal structure is insular with I...F and I...OH₂2 ionic and ion-dipole interactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2309–2314, October, 1985.     

Reaction of N-acetyldehydrophenylalanyl-S-proline with Ca(II) and Ni(II) ions and its role in asymmetric hydrogenation

N-Ac-Phe-S-Pro forms strong coordination complexes with the CO₂H group of the proline residue and weak coordination complexes through the -C(=O)-N groups with Ca(II) and Ni(II) ions in 95% aqueous methanol as indicated by the pK _a values, PMR spectroscopy, and paramagnetic broadening of the¹³C NMR signals in the nickel complex. Complex formation enhances the rigidity of the dehydrodipeptide conformation, leading to a strong increase in the optical yield upon hydrogenation over achiral catalysts.Institute of Food Substances, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1667–1670, July, 1992.     

The effect of anions in the coordination spherè of Mg complexes ofN-acetyldehydrophenylalanyl-(S)-valine on the diastereoselectivity of hydrogenation

Diastereoselective hydrogenation in ethanol over Pd/C ofN-acetyldehydrophenylalanyl-(S)-valine (1) as complexes with Mg salts of strong acids gives predominantlyN-acetyl-(S)-phenylalanyl-(S)-valine (de up to 60%). In the case of complexes of1 with Mg salts of weak acids, the sign of asymmetric induction changes. Data of¹⁹F NMR spectroscopy ofN-acetyldehydro(p-fluorophenylalanyl)-(S)-valine indicate that in the former case, the anion of a strong acid does not enter the coordination sphere of the complex, whereas in the larter case, the anion of the weak acid does. The nature of the solvent also influences the reaction stereoselectivity. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1704–1706, September, 1999.