Nanomolar-Potency 1,2,4-Triazoloquinoxaline Inhibitors of the Kidney Urea Transporter UT-A1

Urea transporter A (UT-A) isoforms encoded by the 100 Slc14a2 gene are expressed in kidney tubule epithelial cells, where they facilitate urinary concentration. UT-Al inhibition is predicted to produce a unique salt-sparing diuretic action in edema and hyponatremia. Here we report the discovery of 1,2,4-triazoloquinoxalines and the analysis of 37 synthesized analogues. The most potent compound, 8ay, containing 1,2,4triazolo[4,3-a]quinoxaline-substituted benzenesulfonamide linked by an aryl ether, rapidly and reversibly inhibited UT-Al urea transport by a noncompetitive mechanism with IC50 approximate to 150 nM; the IC50 was similar to 2 / mu M for the related urea transporter UT-B encoded by the Slc14a1 gene. Molecular modeling suggested a putative binding site on the UT-Al cytoplasmic domain. In vitro metabolism showing quinoxaline ring oxidation prompted the synthesis of metabolically stable 7,8-difluoroquinoxaline analogue 8bl, which when administered to rats produced marked diuresis and reduced urinary osmolality. 8bl has substantially improved UT-Al inhibition potency and metabolic stability compared with prior compounds.