alpha-Glucosidase and Protein Tyrosine Phosphatase 1B Inhibitors from Malbranchea circinata

During a search for new alpha-glucosidase and protein tyrosine phosphatase 1B inhibitors from fungal sources, eight new secondary metabolites, including two anthranilic acid-derived peptides (1 and 2), four glycosylated anthraquinones (3-6), 4-isoprenylravenelin (7), and a dimer of 5,8-dihydroxy-4-methoxy-alpha-tetralone (8), along with four known compounds (9-12), were isolated from solid ricebased cultures of Malbranchea circinata. The structural elucidation of these metabolites was performed using 1D and 2D NMR techniques and DFT-calculated chemical shifts. Compounds 1-3, 9, and 10 showed inhibitory activity to yeast a-glucosidase (aGHY), with IC50 values ranging from 57.4 to 261.3 mu M (IC50 acarbose = 585.8 mu M). The effect of 10 (10.0 mg/kg) was corroborated in vivo using a sucrose tolerance test in normoglucemic mice. The most active compounds against PTP-1B were 8- 10, with IC50 values from 10.9 to 15.3 mu M (IC50 ursolic acid = 27.8 mu M). Docking analysis of the active compounds into the crystal structures of aGHY and PTP-1B predicted that all compounds bind to the catalytic domains of the enzymes. Together, these results showed that M. circinata is a potential source of antidiabetic drug leads.