Bioassay-guided isolation and characterisation of α-glucosidase inhibitors from Sanghuangporus baumii

Bioassay-guided fractionation of the isopropanol extract of the medicinal mushroom Sanghuangporus baumii led to the isolation and characterisation of a new acorane-type sesquiterpenoid bauminene (1) and seven known compounds 2-8. The planar structure of 1 was elucidated on the basis of extensive spectroscopic analysis, including 1D, 2D NMR and HR-ESI-MS. The relative configuration of 1 was determined by a combination of ROESY experiment, density functional theory calculation of C-13 NMR, and DP4+ probability analysis, while the absolute configuration of 1 was established by comparative electronic circular dichroism (ECD) spectra analysis. In the in vitro bioassay, compounds 1-8 exhibited potent to moderate alpha-glucosidase inhibitory activity with IC50 values ranging from 6.8 +/- 0.68 to 221.4 +/- 6.57 mu M. The presences of these bioactive constituents in the sclerotia of S. baumii may be related to the use of the fungus as 'Sanghuang' for the adjuvant treatment of DM.