A pair of new isocoumarin epimers from soil fungus Hypoxylon sp.

Abstract

In our research on novel secondary metabolites from micro-organisms, two new (1–2) and four known dihydroisocoumarins (3–6) were derived from soil fungus Hypoxylon sp. Their structures were determined with extensive NMR data analysis and ECD calculation comparing with those of experimental CD spectra. Interestingly, compounds 1 and 2 possessed the same planar structure and very similar NMR data, suggesting 1 and 2 were a pair of epimers at either C-3 or at C-4, confirmed by the totally opposite cotton effect around 250 nm in the CD spectra of 1 and 2. Moreover, for the first time, we revealed that the CD absorption peak at 250 nm was dominated by C-3 orientation, rather than the orientation of C-3 substituents, by intensive ECD investigations.

Keywords:

• Soil fungus
• isocoumarin
• ECD investigation