Phytochemical characterization of cyclodextrin-elicited in vitro roots of Microchirita involucrata reveals bioactive α-glucosidase inhibitory quinones

Microchirita involucrata is a member of the family Gesneriaceae, a group known for producing diverse secondary metabolites, although phytochemical information for this species remains unexplored. In this study, an in vitro root culture system integrated with cyclodextrin (CD) elicitation was developed to enhance secondary metabolite biosynthesis and secretion. Bioactive constituents were isolated from the elicited culture medium extracts and subjected to comprehensive structural characterization and biological activity evaluation. Repeated CD elicitation induced a pronounced, cycle-dependent accumulation of phytochemicals in the culture medium. This work constitutes the first phytochemical investigation of M. involucrata and reports, for the first time, the isolation and structural characterization of five known compounds—α-dunnione (1), 7-hydroxy-α-dunnione (2), 7-hydroxy-6-methoxy-α-dunnione (3), 2-hydroxy-3-methoxy-7-methylanthraquinone (4), and 2,8-dihydroxy-3-methoxy-7-methylanthraquinone (5)—from this species. All isolated compounds exhibited antioxidant and α-glucosidase inhibitory activities, with compound 3 displaying the highest potency. Notably, compound 3 showed the strongest α-glucosidase inhibition (IC₅₀ = 0.73 ± 0.23 µM), which correlated with its superior antioxidant activity as determined by ABTS (59.90 ± 13.75 µmol Trolox g⁻¹ purified fraction) and FRAP (21.43 ± 1.83 mg ascorbic acid g⁻¹ purified fraction) assays. Integrated molecular docking and FMO analyses revealed that compound 3 displayed enhanced inhibitory potency through strong stabilizing interactions with the key catalytic residues Asp214, Glu276, Asp349, and Arg439 in the α-glucosidase active site. Overall, these findings establish M. involucrata as a previously uncharacterized source of bioactive quinone derivatives and demonstrate the effectiveness of repeated CD elicitation as a strategy for extracellular metabolite production in plant in vitro culture systems.