Identification of New Diterpenoids from the Pulp of Coffea arabica and Their α-Glucosidase Inhibition Activity.

Six new ( 1 , 2 , 3 , 5 , 6 , and 8 ) and seven known ( 4 , 7 , 9 , 10 , 11 , 12 , and 13 ) diterpenoids have been identified in the pulp of Coffea arabica . The structures of new diterpenoids were elucidated by extensive spectroscopic analysis, including 1D, 2D NMR (HSQC, HMBC, 1 H- 1 H COSY, and ROESY), HRESIMS, IR, DP4+, electronic circular dichroism, and X-ray crystallography analysis. Compound 1 is ent -labdane-type diterpenoid, whereas compounds ( 2 - 13 ) are ent -kaurane diterpenoids. The result of α-glucosidase inhibitory assay demonstrated that compounds ( 1 , 3 , 5 , 7 , and 10 ) have moderate inhibitory activity with IC 50 values of 55.23 ± 0.84, 74.02 ± 0.89, 66.46 ± 1.05, 49.70 ± 1.02, and 76.34 ± 0.46 μM, respectively, compared to the positive control (acarbose, 51.62 ± 0.21 μM). Furthermore, molecular docking analysis has been conducted to investigate the interaction between the compounds and the receptors of α-glucosidase to interpret their mechanism of activity. This study is the first investigation that successfully discovered the presence of diterpenoids within the coffee pulp.