Diels–Alder type adducts with potent alpha-glucosidase inhibitory activity from Morus macroura

Two new Diels–Alder type adducts, macrourins I and J (1–2), along with seven known analogues (3–9) were isolated from the stems of Morus macroura Miq. The structures of the two new compounds were elucidated by extensive analysis of spectroscopic data. Compounds 1–9 all showed highly potent in vitro α-glucosidase inhibitory activities, and the IC50 values of compounds 1 and 2 were 1.70 and 1.58 μM, respectively, approximately 800 times stronger than the positive control, acarbose.