Two new xanthones, oblongixanthones I (1) and J (2), and seven known compounds (3-9), were isolated from an EtOAc extract of the twigs of Garcinia oblongifolia. Their structures were elucidated using spectroscopic methods, mainly 1 D and 2 D NMR. The antidiabetic effects of the two new compounds were evaluated using α-glucosidase and PTP1B inhibition assays. Both compounds displayed strong inhibition towards α-glucosidase with IC50 values of 258.7 ± 49.3 and 187.1 ± 27.5 μM, respectively (compared with acarbose, IC50 = 900.0 ± 3.0 μM) and moderate effects against PTP1B with IC50 values of 93.9 ± 12.3 and 64.1 ± 5.8 μM, respectively (compared with RK682, IC50 = 4.4 ± 0.3 l μM).
Keywords: Garcinia oblongifolia; PTP1B; Type 2 diabetes; xanthones; α-glucosidase.