Bioassay Guided Isolation and α-Glucosidase Inhibition Studies of a New Sesquiterpene from Ochradenus aucheri.

Aims: The aim of the current study was to explore the anti-diabetic potential of Ochradenus aucheri Boiss (O. aucheri).

Method: All the fractions of O. aucheri were evaluated for α-glucosidase inhibition, followed by bioassay-guided isolation which resulted in a new sesquiterpenoid, as a potential α-glucosidase inhibitor.

Results: The preliminary screening showed that all the fractions including n-hexane (38.0 ± 1.38 μg/mL), dichloromethane (92.6 ± 6.18 μg/mL), ethyl acetate (29.2 ± 0.51 μg/mL) and n-butanol (361.8 ± 5.80 μg/mL) displayed significant α-glucosidase inhibitory activity. The activity-directed fractionation and purification of ethyl acetate fraction led to the isolation of one new sesquiterpenoid, Jardenol (1), and two known metabolites: β-stitosterol-3-O-β-D-glucopyranoside (2) and β-Sitosterol (3). To the best of our knowledge, these metabolites have not been isolated from this plant previously. The structure of the new metabolite 1 was confirmed through 1D and 2D NMR spectroscopy, and MS analysis. Compound 1 showed significant α-glucosidase inhibition with an IC50 value of 138.2 ± 2.43 μg/mL as compared to positive control acarbose (IC50 = 942.0 ± 0.60 μg/mL). Additionally, in-silico docking was employed to predict the binding mechanism of compound 1 in the active site of the target enzyme, α-glucosidase. The docking results suggested that the compound forms strong interactions at the catalytic site of α-glucosidase.

Conclusion: The results of the present study indicated that the newly purified secondary metabolite, Jardenol, can be a promising anti-diabetic compound.