<jats:title>ABSTRACT</jats:title><jats:p>One new cytochalasan alkaloid, chaetoglobosin V<jats:sub>b</jats:sub> (<jats:bold>1</jats:bold>), together with two structurally related known compounds, chaetoglobosin V (<jats:bold>2</jats:bold>) and chaetoglobosin G (<jats:bold>3</jats:bold>), was isolated from the ethyl acetate extract of a culture of the endophytic fungus <jats:italic>Chaetomium globosum</jats:italic>, associated with the leaves of <jats:italic>Ginkgo biloba</jats:italic> 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 V<jats:sub>b</jats:sub> (<jats:bold>1</jats:bold>) was established by means of electronic circular dichroism (CD) spectroscopy, on the basis of the comparison between the CD spectrum of (+)‐<jats:bold>1</jats:bold> with that calculated with time‐dependent density functional theory method for a simplified model. The correlation between compounds <jats:bold>1diss</jats:bold>, <jats:bold>2</jats:bold>, <jats:bold>3</jats:bold> was demonstrated by a biomimetic transformation of chaetoglobosin G (<jats:bold>3</jats:bold>) under mild conditions in chaetoglobosins V and V<jats:sub>b</jats:sub> (<jats:bold>1</jats:bold> and <jats:bold>2</jats:bold>). The isolated metabolites were tested against some phytopathogens. <jats:italic>Chirality 24:668–674, 2012</jats:italic>. © 2012 Wiley Periodicals, Inc.