Annulohypoxylon stygium, a Pandanus simplex-associated fungal endophyte with α-glucosidase inhibitory activity

Fungal endophytes offer structurally diverse and unique secondary metabolites with interesting biological activities. Several reports have shown the potential of fungal endophytes as sources of α-glucosidase inhibitors to alleviate diabetes. In this study, the fungal endophyte Annulohypoxylon stygium (Xylariales, Ascomycota) was identified for the first time from the leaves of the endemic tropical plant, Pandanus simplex Merr. Crude extract was obtained by fermenting the fungal endophyte in Potato Dextrose Broth for 30 days at room temperature. The A. stygium crude extract exhibited good inhibition to the α-glucosidase enzyme with an IC50 of 31.88 ± 2.86 µg/mL. Purification of the crude extract afforded 8-methoxynaphthol with an IC50 value of 676.3 ± 1.03 µg/mL. The isolation of 8-methoxynaphthol from A. stygium is reported herein for the first time. This study highlights the ability of A. stygium to produce metabolites that may be useful as antidiabetic drugs.