A series of novel benzothiadiazine 1,1-dioxide derivatives were synthesized and tested for their inhibitory activity against aldose reductase. Of these derivatives, 17 compounds, having a substituted N2-benzyl group and a N4-acetic acid group on the benzothiadiazine, were found to be potent and selective aldose reductase inhibitors in vitro with IC50 values ranging from 0.032 to 0.975 μM. 9m proved to be the most active in vitro. The eight top-scoring compounds coming from the in vitro test for ALR2 inhibition activity were then tested in vivo, whereby three derivatives, 9i, 9j, and 9m, demonstrated a significantly preventive effect on sorbitol accumulation in the sciatic nerve in the 5-day streptozotocin-induced diabetic rats in vivo. Structure-activity relationship and molecular docking studies highlighted the importance of substitution features of N4-acetic acid group and halogen-substituted N2-benzyl group in the benzothiadiazine scaffold and indicated that substitution with hallogen at C-7 had a remarkably strong effect on ALR2 inhibition potency.

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A novel and facile synthesis of quinoxalinone derivatives was developed in which a wide range of 3-chloroquinoxalin-2(1H)-ones as key intermediates can be generated chemo- and regioselectively in good yields from corresponding quinoxaline-2,3(1H,4H)-diones. This new protocol is arguably superior, as it allows the design and preparation of a variety of bioactive quinoxaline-based compounds, which are particularly effective in the treatment of diabetes and its complications. Through this procedure, a new class of quinoxalinone-based aldose reductase inhibitors were synthesized successfully. Most of the inhibitors, with an N1-acetic acid head group and a substituted C3-phenoxy side chain, proved to be potent and selective. Their IC(50) values ranged from 11.4 to 74.8 nM. Among them, 2-(3-(4-bromophenoxy)-7-fluoro-2-oxoquinoxalin-1(2H)-yl)acetic acid and 2-(6-bromo-3-(4-bromophenoxy)-2-oxoquinoxalin-1(2H)-yl)acetic acid were the most active. Structure-activity relationship and molecular docking studies highlighted the importance of the ether spacer in the C3-phenoxy side chains, and provided clear guidance on the contribution of substitutions both at the core structure and the side chain to activity.

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