Structure-Based design of Marine-derived Meridianin C derivatives as glycogen synthase kinase 3β inhibitors with improved oral bioavailability: From aminopyrimidyl-indoles to the sulfonyl analogues.

Glycogen synthase kinase 3β (GSK-3β) has become an attractive target for the treatment of diabetes. Compound I is an indole-based GSK-3β inhibitor designed from the Meridianin C, a marine natural product (MNP) isolated from Aplidium meridianum. However, this compound has a moderate inhibitory activity toward GSK-3β (IC = 24.4 μM), moderate glucose uptake (38%), and especially, a low oral bioavailability (F = 11.4%). In the present study, applying the structure-based design strategy, a series of derivatives modified on the indole moiety were synthesized based on the lead compound I, followed by evaluating their cytotoxic activity, antihyperglycemic activity, and kinase inhibitory activity. Among this series, compound 6x with a sulfonyl group displayed the highest glucose uptake (83.5%) in muscle L6 cells, showing much higher inhibitory activity against GSK-3β (IC = 5.25 μM). Molecular docking indicated that compound 6x was properly inserted into the ATP-binding binding pocket of GSK-3β with a higher docking score (-8.145 kcal/mol) compared with that of compound I (-6.950 kcal/mol), interpreting the higher kinase inhibitory activity toward GSK-3β. Remarkably, compound 6x showed favorable drug-like properties, including significantly better oral bioavailability (F = 47.4%) and no two-week acute toxicity at a dose of 1 g/kg. Our findings suggest that these MNP-derived sulfonyl indole derivatives could be used as lead compounds for the development of anti-hyperglycemic drugs.