Selective synthesis and comparative activity of olefinic isomers of 1,2-benzothiazine-1,1-dioxide carboxylates as aldose reductase inhibitors

Abstract

α,β- and β,γ-unsaturated carboxylate isomers of 1,2-benzothiazine-1,1-dioxide were selectively synthesized via the Wittig olefination reaction under various temperature conditions. At 40 °C, α,β-unsaturated esters with high Z-stereoselectivity (83–87%) were formed, while β,γ-unsaturated esters formed preferentially with moderate to excellent regioselectivity at 100–120 °C (77–96%). The acid isomers were found to inhibit aldose reductase in order of activity β,γ-unsaturated > Z-α,β-unsaturated > E-α,β-unsaturated isomers. The β,γ-unsaturated isomer 7b, 2-[2-(4-bromo-2-fluorobenzyl)-1,1-dioxido-2H-1,2-benzothiazin-4(3H)-ylidene]acetic acid, exhibited the most potent inhibition activity, with an IC₅₀ value of 0.057 μM. This was further supported by docking studies.