Systematical NMR analysis of swainsonine, a mycotoxin from endophytic fungus Alternaria oxytropis

Abstract

Swainsonine (SW, 1), a unique indolizine with poly-hydroxyl groups, was re-isolated from the plant endophytic fungus Alternaria oxytropis. The structure (including planar structure and relative configuration) was systematically elucidated by NMR spectra (including ¹ H, ¹³ C, ¹ H-¹ H COSY, HMQC, HMBC, and NOESY spectra in DMSO-d₆ and in CD₃ OD); ¹ H NMR spectra of the modified Mosher's products were first used to determine the absolute configuration of SW. More importantly, the complex coupled features of H-7α, H-7β, and H-6α in the ¹ H NMR spectrum of (1) were analyzed in details, which will provide aids for the planar and relative configuration determination of analogs.

Keywords: Alternaria oxytropis; NMR; endophytic fungus; structural elucidation; swainsonine.