New ent-kaurane diterpenes from the roasted arabica coffee beans and molecular docking to α-glucosidase

Ten new (1-10) and five known (11-15) ent-kaurane diterpene derivatives were identified from the roasted beans of coffea arabica. Their structures were established by extensive spectroscopic analysis including 1D, 2D NMR (HSQC, HMBC, COSY, and ROESY), HRESIMS, and X-ray diffraction analysis. Compounds 1-3 were three types of rearranged ent-kaurane diterpenes, and compounds 4 and 5 were diterpene esters with a rare 6-hydroxyhexanoyl at C-17. Compounds 6, 8, 14, and 15 showed moderate inhibitory effect on α-glucosidase with IC₅₀ values of 149.92 ± 2.52, 23.23 ± 1.03, 54.58 ± 4.21, 54.16 ± 3.95 μM, respectively, compared to the positive control (60.71 ± 16.45 μM). The results of activity assay showed that diterpenes with the double bond between C-15 and C-16 exhibited stronger α-glucosidase inhibitory activity. Further molecular docking experiments were adopted to discuss the mechanism of activity.