Isolation, semi-synthesis, docking-based prediction, and bioassay-based activity of Dolichandrone spathacea iridoids: new catalpol derivatives as glucosidase inhibitors

Abstract

Dolichandrone spathacea iridoids are promising anti-diabetic inhibitors towards α-glucosidase protein (PDB-3W37) and oligo-1,6-glucosidase protein (PDB-3AJ7). Five catalpol iridoids (1, 2, 10, 13, 14) were isolated from mangrove plant D. spathacea, and their derivatives (3, 4, 5, 6, 7, 8, 9, 11, 12, 15) were obtained from reduction, acetylation, O-alkylation, acetonisation, or hydrolysation starting from naturally isolated compounds. They were identified by spectral methods such as IR, MS, and 1D and 2D NMR. Their glucosidase-related (3W37 and 3AJ7) inhibitability and physiological compatibility were predicted by molecular docking simulation and prescreened based on Lipinski's rule of five. Experimental α-glucosidase inhibition of 1–15 was evaluated using enzyme assays. Compounds 3, 4, 5, 6, and 9 are new iridoid derivatives, introduced to the literature for the first time, while all fifteen compounds 1–15 are studied for molecular docking for the first time. Regarding protein 3W37, the five strongest predicted inhibitors assemble in the order 2 > 10 > 1 > 9 > 14. In respect to 3AJ7, the corresponding order is 14 > 2 > 10 > 5 > 1 = 9. Lipinski's criteria suggest 10 as the candidate with the most potential for oral administration. The in vitro bioassay revealed that compound 10 is the most effective inhibitor with a respective IC₅₀ value of 0.05 μM, in the order 10 > 2 > 14 > 13 > 1. The computational and experimental results show good consistency. The study opens an alternative approach for diabetes treatment based on inhibitability of natural and semi-synthesised catalpol iridoid derivatives towards carbohydrate-hydrolases.