Novel Diterpenoids from Yemeni Coffea arabica : Isolation, Structural Elucidation, and Glucose Uptake Activity

A phytochemical investigation of Yemeni Coffea arabica green beans led to the isolation of fifty-one diterpenoids, including 18 new compounds (1–5, 9–15, 26, 27, 31, 33, 34, 42). Structures were established by 1D/2D NMR, HRESIMS, IR, and X-ray crystallography. Compound 11 possesses a novel rearranged skeleton, while compounds 1–15 represent a series of diterpenoid glycosides featuring diverse aromatic acylations (p-hydroxybenzoyl, p-coumaroyl, feruloyl, sinapoyl, or 6,7-dimethoxycinnamoyl) on a C-19 β-glucosyl moiety. Bioactivity screening in insulin-resistant HepG2 cells identified nine compounds that significantly enhanced glucose uptake, with improvements ranging from 24.91% to 81.10%. This study elucidates the structural diversity of diterpenoids in coffee and highlights their potential relevance to glucose metabolism.