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Paper | Regular issue | Vol 89, No. 7, 2014, pp.1620-1631
Published online, 27th May, 2014
DOI: 10.3987/COM-14-13003
Stereochemical Assignment of Four Diastereoisomers of 3,4-Dimethylpyroglutamic Acid, a Moiety of Callipeltin B

Mari Kikuchi and Hiroyuki Konno*

*Graduate School of Science and Engineering, Yamagata University, 3-16 Jonan 4-Chome, Yonezawa 992-8510, Japan

Abstract

The synthesis and stereochemical assignment of four diastereoisomers of 3,4-dimethylpyroglutamic acid (pDME) (1) are described. Stereo-divergent synthesis of four pDMEs (1) was achieved starting from Thottathil’s synthon and Garner’s aldehyde for comparison of synthetic pDMEs (1) by 1H NMR analysis and CD spectra. The stereochemistry of pDME (1) in cyclic depsipeptide callipeltin B (2) with cytotoxic and anti-HIV activities was confirmed to be 2S,3S,4R. Coupling constant between H2 and H3 of synthetic (2S,3S,4R)-pDME (1a) showed a smaller value than those of other isomers. In addition, synthetic pDMEs (1) hardly showed cytotoxicity against HeLa cells.