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■ Synthetic Studies on Callipeltins: Stereoselective Syntheses of (3S,4R)-3,4-Dimethyl-L-pyroglutamic Acid and Fmoc-D-allothreonine from Serine Derivatives

Hiroyuki Konno,* Yoko Takebayashi, Kazuto Nosaka, and Kenichi Akaji

*Yamagata University, 3-16 Jonan 4-Chome, Yonezawa 992-8510, Japan

Abstract

The non-proteinogenic amino acids contained in callipeltins, (3S, 4R)-3, 4-dimethyl-L-pyroglutamic acid and D-allothreonine, were synthesized from D- or L-serine. The stereoselective synthesis of two methyl groups of (3S, 4R)-3, 4-dimethyl-L-pyroglutamic acid was accomplished by diastereoselective hydrogenation and alkylation. Kinetic epimerization of the C-4 methyl substituent followed by Boc-deprotection with 10% TFA gave the desired (3S, 4R)-3, 4-dimethyl-L-pyroglutamic acid as a single isomer.