Aldose reductase (AR) is an NADPH dependent enzyme that catalyses the reduction of the aldehyde to the corresponding alcohols. Diabetic complications including neuropathy, nephropathy, cataracts and retinopathy are considerately caused by accumulation of sorbitol, which is produced from glucose by AR in polyol pathway. The aim of AR inhibitor therapy is to normalize the elevated flux of blood and sorbitol through the polyol pathway in the target tissue. A large number of inhibitors have been prepared synthetically, and some of them are used therapeutically. However, none of them is satisfactory. From the plants, many AR inhibitors have been found, which are discussed in this review. By the structure based functioning of AR and its inhibitors, some will be developed promising in the treatment of diabetic complications. The main structural features of the inhibitors will be a polar head group and a hydrophobic ring system. The plants that contain the AR inhibitors may prevent from diabetic complications.
The keto-enol tautomerism of some P-dicarbonyl compounds, including ethyl acetoacetate (1 ), acetylacetone (2), benzoylacetone (3), dibenzoylmethane (4), and 1,1,1 -trifluoro-3-(2-thenoy1)acetone ( 5 ) , has been investigated in various solvents at 25 "C, by using low-temperature (-20 to -50 "C) highperformance liquid chromatography (h.p.1.c.) for analytical measurements. Base-line separation of keto and enol tautomers of these compounds has been achieved on silica gel packings with a mobile phase composed of hexane and propan-1 -01 containing a small amount of acetic acid. The ratios of keto and enol tautomers in different solvents have been determined; the percentages of enol tautomers have been found to be higher in polar solvents, in accord with n.m.r. data previously reported. In all solvents the proportions of enol tautomers of acetylacetone derivatives have been found to increase in the following order; ( 2 ) < (3) < (4); this has been attributed to the fact that enol tautomers of phenyl-substituted acetylacetones have been stabilized, owing to the formation of extended conjugated systems. For the ester ( I ) , the presence of a very small amount of a third tautomer (0.1%) has been found, probably an unconjugated enol tautomer.
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