Stereochemical assignment of four diastereoisomers of 3,4- dimethylpyroglutamic acid, A moiety of callipeltin B

Article abstract of DOI:10.3987/COM-14-13003

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.