All desired compounds with a carboxylic

All desired compounds with a carboxylic Salirasib substituent at N1 position of the quinoxalinone scaffold and a variety of aromatic substituents at C3 position were obtained by the syntheses starting from methoxy-substituted 3-chloro-quinoxalin-2(1)-ones () prepared as previously. As shown in , compounds with a C6 or C7methoxyl group were alkylated with methyl bromoacetate at the N1 position to form methyl esters as key intermediates. Then the Suzuki coupling provided compounds with the introduction of different phenyl groups at the C3 position in good yields. Direct hydrolysis of with lithium hydroxide or demethylation of the C6- and C7-methoxyl with BBr followed by hydrolysis both yielded the end products . To construct longer C3 side chains, different styryl groups were attached to the C3 position of the intermediates by Heck coupling reaction forming compounds , which were hydrolyzed directly or deprotected with demethylation reagent BBr before hydrolysis to form compounds as ARI candidates. The acids were further synthesized through the Pd/C hydrogenation reaction and subsequently hydrolysis from compounds to give the carbon-carbon single bond spacer. The synthetic phenolic hydroxyl containing target compounds include three series categorized by the C3 spacer. The first series compounds possess substituted phenyl rings directly attached to the C3 position, while the other two series compounds and have a spacer of two atoms. All designed compounds were tested for their potential inhibition against ALR2 isolated from rat lenses and ALR1 isolated from rat kidneys. IC (μM) or the percentage of enzyme inhibition (%) were applied to express the results of ARL2 and ARL1 inhibitions, respectively, as summarized in . The validity of the results was assessed with respect to epalrestat as a positive ARI, and compounds reported previously were retested along with the newly synthesized compounds for structure–activity relationship (SAR) studies (). Most of compounds showed ALR2 inhibitory activity with IC values at submicromolar level. Comparison of with revealed that either the position or number of phenolic hydroxyl group boosted the potency of ALR2 inhibition. The phenolic hydroxyl in C3 phenyl ring had an effect on ALR2 inhibition with the rank order of 2,4,6-(OH)>2,4-(OH)>2,5-(OH)>4-OH>3-OH. The phenolic trihydroxyl compounds and phenolic dihydroxyl compounds ( and ) showed an obvious enhancement in ALR2 inhibition compared with the single phenolic hydroxyl compounds ( and ). Moreover, demethylation of the methoxyl group at the C6 or C7 position of quinoxalinone core in compounds and leading to and resulted in an obvious enhancement in the inhibitory activity. Different substituents on the phenyl ring of the core structure had a significant effect on ALR2 inhibition compared with unsubstituted compound , and among them the C7-phenolic hydroxyl was the most effective by comparison of compounds , , and . However, the C6-methoxyl showed a negative effect on ALR2 inhibition when comparing with and with , respectively. Therefore, it is reasonable to conclude that the introduction of phenolic hydroxyl either to the C3 side chain or the core structure in compounds may enhance ALR2 inhibitory activity. Compounds with carbon-carbon double bond C3 spacer were proved to have good activity on ALR2 inhibition. Of them, was the most active with an IC value of 0.059μM and was more potent than epalrestat. Introduction of phenolic hydroxyl group to the C3 styryl ring could enhance the inhibitory activity when comparing with other compounds in this series. SAR studies at the substituents of C3 side chain manifest that the 4-hydroxyl ( and ) was more active than the combination of 3-methoxyl and 4-hydroxyl ( and ). Moreover, further demethylation of the methoxyl group both on the C3 styryl ring and the core structure of compounds and increased the inhibitory activity ( and ). In this series, all the phenolic hydroxyl containing compounds showed excellent ALR2 inhibitory activity. Further hydrogenation of the C3-double bonds identified the function of the vinyl spacer. The reduction products were less effective than their precursors and , which indicated that the carbon-carbon double bond spacer had a positive effect on the activity compared with the single bond spacer. Also, it was confirmed that the extended C3 vinyl spacer had a great improvement on ARL2 inhibition, which was deduced by comparing compounds with their counterparts in compounds .