Phytochemical investigation of the trunks of Coffea canephora yielded two new ent-kaurane diterpene diastereomers, which have been named coffecanepholide A, ent-3β,16β,17-trihydroxykauran-18-al (1) and coffecanepholide B, ent-3β,16β,17-trihydroxykauran-19-al (2). Structural elucidation and configurational assignment were deduced from extensive spectroscopic NMR/HRESIMS analysis and by comparison with the spectral data of the literature relevant structures. The isolated compounds were assayed for in vitro inhibitory activities against α-glucosidase. Structure 2 showed the α-glucosidase inhibitory activity with an IC50 value of 294.7 ± 0.9 μM, while compound 1 exhibited inactivity. In addition, the docking results revealed that structure 2 can form more interactions with amino acid residues at the active site of α-glucosidase, which gave a more negative binding energy (-9.56 kcal/mol) compared with 1 (-8.60 kcal/mol). This observation might be responsible for a better activity of 2 against α-glucosidase.
Keywords: Coffea canephora; NMR analysis; diastereomers; diterpene; docking; ent-kaurane skeleton; α-glucosidase inhibition.