Diastereotopic labdane diterpenoids from rhizomes of Hedychium coronarium with α-glucosidase activity and their molecular docking study

Two new diastereotopic labdane diterpenoids (+)-(5 S,9 S,10 S,15 R) coronarin D methyl ether (1) and (-)-(5 R,9 R,10 S,15 S) coronarin D methyl ether (2) were isolated from the rhizomes of Hedychium coronarium J. Koeing along with seven labdane diterpenoids including an epimeric mixture of coronarin D (3). The diastereomers (1) and (2) were successfully separated and purified from their mixture by recycling high performance liquid chromatography (RHPLC) and characterized using 1D and 2D NMR, MS and FTIR analyses. The absolute configuration of the stereocenters in the two compounds (1 and 2) was determined through rotating frame overhauser spectroscopy (ROESY) analysis. The compounds were evaluated for invitro α-glucosidase inhibitory activity and they showed excellent inhibitory activities against the enzyme with IC₅₀ values ranging from 23 to 112 nM. The binding interactions of the compounds with crucial amino acid residues in the active sites of the α-glucosidase enzyme in silico were investigated through molecular docking study using the Autodock package.