ASYMMETRIC HYDROGENATIONS OF<i>N</i>-PYRUVOYL-(<i>S</i>)-AMINO ACID ESTERS BY USING SODIUM BOROHYDRIDE. A SOLVENT EFFECT
作者:Toratane Munegumi、Kaoru Harada
DOI:10.1246/cl.1983.1225
日期:1983.8.5
N-Pyruvoyl-(S)-amino acid isobutyl esters were hydrogenated with sodiumborohydride(NBH) in several alcoholic solvents, and N-[(R)-lactoyl]-(S)-amino acid esters were obtained with diastereoisomeric purity of up to 44%. Significant solventeffect on the diastereoisomeric purity of the product was observed.
N-[(R)-Lactoyl]-(S)-amino acid isobutyl esters were obtained with a diastereoisomeric purity up to 34%, through the catalytic hydrogenations of N-pyruvoyl-(S)-amino acid (alanine, valine, and leucine) isobutyl esters over palladium on charcoal. It was found that a linear correlation exists between the dielectric constant of the solvent and the diastereoisomeric purity of the product obtained by catalytic hydrogenation. The ratio of N-[(S)-lactoyl]-(S)-amino acid isobutyl ester to N-[(R)-lactoyl]-(S)-amino acid isobutyl ester increased with the decrease of the dielectric constant of the solvent. This solvent effect could be explained by the chelation mechanism. The temperature effect on the asymmetric catalytic hydrogenation was also studied.