Unusual ent -Kaurane Diterpenes from the Coffea Cultivar S288 Coffee Beans and Molecular Docking to α-Glucosidase.

A total of 11 new ( 1 - 11 ) and 2 known ( 12 and 13 ) ent -kaurane diterpene derivatives were identified from the roasted beans of Coffea cultivar S288. Their structures were established by extensive spectroscopic analysis, including one- and two-dimensional nuclear magnetic resonance (heteronuclear single-quantum correlation, heteronuclear multiple-bond correlation, correlation spectroscopy, and rotating-frame Overhauser enhancement spectroscopy), high-resolution electrospray ionization mass spectrometry, and X-ray analyses. Cafespirone acid A ( 1 ) represents the first example of diterpene featuring a spirocyclic skeleton constructed from a 6/6/5 tricyclic system. Cafeane acid A ( 2 ) possesses a 6/6/6/5 tetracyclic system as a result of the C/D ring rearrangement. Furthermore, compounds 1 - 12 were evaluated for their α-glucosidase inhibitory activity. The results showed that compounds 2 , 4 , 5 , 6 , 7 , 10 , and 11 had a moderate inhibitory effect on α-glucosidase, and half-maximal inhibitory concentration values of compounds 4 , 6 , 7 , and 10 were 18.76 ± 1.46, 4.88 ± 0.03, 12.35 ± 0.91, and 12.64 ± 0.59 μM, respectively, compared to the positive control acarbose (60.71 ± 16.45 μM). Additionally, the molecular docking experiments showed that the carbonyl group at C-19 of compounds 4 , 6 , and 7 formed strong hydrogen bonds with ARG315, which may make them have moderate inhibitory activity.