Alkaloids from the Fungus Penicillium spathulatum as α-Glucosidase Inhibitors

Benzomalvin A (1), quinolactacins A1 (2), A2 (3) and B (4), quinolonimide (5), asperphenamate (6), and a new halogenated polyhydroxyanthraquinone, namely 2-chloro-6-[2'(S)-hydroxypropyl]-1,3,8-trihydroxy-anthraquinone (7), were isolated from an organic extract obtained from the solid culture of Penicillium spathulatum B35. Compounds 2 and 3 were isolated as an epimeric mixture, and compound 4 as a racemate. The structure of 7 was elucidated using 1D and 2D NMR, combined with computational methods (density functional theory). Compound 1, the mixture of 2 and 3, racemate 4, and compound 6 inhibited the yeast α-glucosidase in a concentration-dependent fashion with IC50 values of 383.2, 273.3, 57.3, and 8.3 µM, respectively. The α-glucosidase inhibitory properties of 1 were confirmed in vivo with an oral sucrose tolerance test in normal and hyperglycemic mice (p < 0.05). Furthermore, docking studies predicted that the most stable conformers of 1 bind to yeast and mammalian α-glucosidases with a higher affinity than acarbose. Finally, 1 also showed antihyperalgesic activity when tested in the formalin assay in hyperglycemic mice (p < 0.05).