Sesquiterpenes from Curcuma zedoaria (Christm.) Rosc. Rhizomes and Their Alpha-Glucosidase Inhibitory Effects

Curcuma zedoaria (Christm.) Rosc. is a popular traditional herb to treat digestive disorders in Asian tropical countries. Previous studies indicated the presence of sesquiterpenoids, diterpenoids, and curcuminoids with various bioactivities. To enrich the phytocomposition data of this plant, this investigation was conducted.<br/>The dried rhizomes of C. zedoaria were collected in Hai Phong City (Vietnam), extracted with methanol and fractionated with n-hexane, CH₂Cl₂, and EtOAc. Compounds were isolated from n-hexane soluble fraction by open column chromatography combined with thin layer chromatography from fraction n-hexane. Their chemical structures were elucidated by 1D, and 2D NMR spectra and comparison with reported data. As a result, a phytochemical investigation was conducted to isolate six sesquiterpenes from C. zedoaria. Their chemical structures were elucidated to be curcumenol (1), procurcumenol (2), neoprocurcumenol (3), 13-hydroxygermacrone (4), zederone (5), and curcumalactone (6). Among isolated compounds, compounds 1, 2, 4, and 5 were reported from C. zedoaria. Meanwhile, neoprocurcumenol (3) and curcumalactone (6) are isolated from this species for the first time. Compound 5 exhibited a mild inhibitory effect on α-glucosidase with an IC₅₀ of 99.45 ± 0.50 μg/mL.