An asymmetric transformation from l-histidine [l-His] to d-His was achieved by using salicylaldehyde as a catalyst for epimerization, and (2R, 3R)-tartaric acid as a resolving agent, in acetic acid. Treatment of the obtained salt with triethylamine in methanol gave d-His with 100% optical purity in 95% yield based on the starting l-His.
The racemization rates of N-acetyl-(S)-tyrosine, N-acetyl-(S)-phenylalanine, N-acetyl-(R)-2-(4-hydroxyphenyl)glycine [(R)-AcHpg], N-acetyl-(R)-2-phenylglycine, and N-acetyl-(S)-alanine were measured by use of (RS)-α-methylbenzylamine [(RS)-MBA] as a base-catalyst. The first-order rate constant for racemization tended to increase with an increase in the polar substituent constant of the N-acetylamino acid side chain. The racemization appeared to be subject to the inductive effect by the side chain. An asymmetric transformation of (RS)-AcHpg by using (R)-MBA, based on the result of racemization, gave an optically pure salt of (R)-AcHpg with (R)-MBA by successive use of the filtrate as the solvent. Optically pure (R)-2-(4-hydroxyphenyl)glycine [(R)-Hpg] was separated from the salt in 87–90% yield based on the starting (RS)-AcHpg. In addition, the asymmetric transformation of (R)-AcHpg was achieved by using (S)-MBA to give optically pure (S)-Hpg in 80% yield after purification of the salt of (S)-AcHpg with (S)-MBA followed by hydrolysis.
Facile Production of D-Histidine by Asymmetric Transformation of L-Histidine.-Asymmetric transformation of the readily accessible (S)-histidine into its less accessible enantiomer is achieved using salicylaldehyde as the catalyst of epimerization and (R,R)-tartaric acid as the resolving agent. -(SHIRAIWA, T.; SHINJO, K.; MASUI, Y.; OHTA, A.; NATSUYAMA, H.; MIYAZAKI, H.; KUROKAWA, H.; Bull. Chem. Soc. Jpn. 64 (1991) 12, 3741-3742; Fac. Eng., Kansai Univ.,
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