Molecular networking-assisted isolation of chlorophenolic glycosides from the rhizomes of Curculigo orchioides and their inhibitory effect on α-glucosidase.

Molecular networking analysis and in silico tools, such as Network Annotation Propagation (NAP) and MolNetEnhancer, were applied to explore bioactive constituents present in the ethyl acetate-soluble fraction of the rhizomes of Curculigo orchioides. Among the molecular networks, the most abundant cluster was classified as a phenolic glycoside using the ClassyFire module of MolNetEnhancer. Further, the major node in this cluster was accurately predicted as curculigine A using the in silico fragment analysis tool, NAP. Six undescribed chlorophenolic glycosides (1-6) and 11 known phenolic glycosides were isolated, using molecular networking-assisted isolation methods, and their structures were elucidated using 1D, 2D-NMR and HRESIMS. In particular, the structures of the isolated chlorophenolic glycosides, which have non-protonated aromatic rings, were determined using various NMR experiments, such as 1D-selective NOE, ROESY, and LR-HMBC, and acid hydrolysis. All isolated compounds were examined to determine their inhibitory effects on α-glucosidase and compounds 3, 8, 10, 11, 13, 14, and 16 revealed the IC values ranging from 19.6 to 35.5 μM. Their structure-activity relationships were also evaluated based on the analysis of their inhibitory effects and performance of molecular docking simulations.