Chaetoglobosin Vb from Endophytic Chaetomium Globosum: Absolute Configuration of Chaetoglobosins

One new cytochalasan alkaloid, chaetoglobosin Vb (), together with two structurally related known compounds, chaetoglobosin V () and chaetoglobosin G (), was isolated from the ethyl acetate extract of a culture of the endophytic fungus Chaetomium globosum, associated with the leaves of Ginkgo biloba tree. The structures of the isolated compounds were elucidated by spectroscopic methods including 1D and 2D NMR and mass spectrometry. The absolute configuration of chaetoglobosin Vb () was established by means of electronic circular dichroism (CD) spectroscopy, on the basis of the comparison between the CD spectrum of (+)- with that calculated with time-dependent density functional theory method for a simplified model. The correlation between compounds was demonstrated by a biomimetic transformation of chaetoglobosin G () under mild conditions in chaetoglobosins V and Vb ( and ). The isolated metabolites were tested against some phytopathogens. Chirality 24:668674, 2012. (c) 2012 Wiley Periodicals, Inc.