Benzopyrazines: Synthesis, Characterization and Evaluation as Aldose Reductase Inhibitors

Role of aldose reductase (ALR2) in diabetic complications such as retinopathy, nephropathy, neuropathy, and cataract etc. is well-evident. ALR2 in the first step of polyol pathway reduces glucose to sorbitol whose elevated level leads to diabetic cataract, characterize by clouding of the lens in the eye that affects vision. Inhibition of ALR2 enzyme with small molecules as inhibitor is a rapid approach for diabetic management. In the present study the synthetic route to synthesize desired benzopyrazines and a library of sixteen (16) methyl benzopyrazines were screened against aldose reductase. From the bioactivity results, the 3'-hydroxyphenyl benzopyrazine 6l was found most active (IC₅₀ = 1.34 ± 0.07 µM) while 3'-bromophenyl analogue 6i showed comparable activity for ALR2 (IC₅₀ = 3.48 ± 0.66 µM) as compared to standard sorbinil (IC₅₀ = 3.14 ± 0.02 µM). Both compounds (6l and 6i) showed excellent selectivity for ALR2 over aldehyde reductase (ALR1) which has important role in detoxification of toxic aldehydes. The structure of two regio-isomers were fully characterize by ¹H and ¹³C NMR two dimensional NMR techniques including COSY, NOESY, HSQC, and HMBC. Regio-isomers separation was proved to be difficult in different solvent systems. Only an isomer of 3'-bromo benzopyrazine 6i' was isolated that help to assign the structure of regioisomers from NMR data. All the benzopyrazines were fully characterized by using different spectral techniques including ¹H, ¹³C NMR, IR spectroscopy, and mass spectrometry.