An inhibitor of human liver glycogen phosphorylase a (HLGPa) has been identified and characterized in vitro and in vivo. This substance, [R-(R*,S*)]-5-chloro-N-[3-(dimethylamino)-2-hydroxy-3-oxo-1-(phenylmethyl)propyl]-1H-indole-2-carboxamide (CP-91149), inhibited HLGPa with an IC 50 of 0.13 M in the presence of 7.5 mM glucose. CP-91149 resembles caffeine, a known allosteric phosphorylase inhibitor, in that it is 5-to 10-fold less potent in the absence of glucose. Further analysis, however, suggests that CP-91149 and caffeine are kinetically distinct. Functionally, CP-91149 inhibited glucagon-stimulated glycogenolysis in isolated rat hepatocytes (P < 0.05 at 10-100 M) and in primary human hepatocytes (2.1 M IC 50 ). In vivo, oral administration of CP-91149 to diabetic ob͞ob mice at 25-50 mg͞kg resulted in rapid (3 h) glucose lowering by 100-120 mg͞dl (P < 0.001) without producing hypoglycemia. Further, CP-91149 treatment did not lower glucose levels in normoglycemic, nondiabetic mice. In ob͞ob mice pretreated with 14 C-glucose to label liver glycogen, CP-91149 administration reduced 14 C-glycogen breakdown, confirming that glucose lowering resulted from inhibition of glycogenolysis in vivo. These findings support the use of CP-91149 in investigating glycogenolytic versus gluconeogenic f lux in hepatic glucose production, and they demonstrate that glycogenolysis inhibitors may be useful in the treatment of type 2 diabetes.

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We report here on the discovery path that led to a structurally unprecedented non-hydantoin, non-carboxylic acid aldose reductase inhibitor, 24, which shows remarkably potent oral activity in normalizing elevated sorbitol levels and, more significantly, fructose levels in the sciatic nerve of chronically diabetic rats, with ED(90) values of 0.8 and 3 mpk, respectively. It is well absorbed in rats (oral bioavailability, 98%) and has a long plasma t(1/2) (26 +/- 3 h).

Discovery of a highly selective, potent, and safe non-carboxylic acid, non-hydantoin inhibitor of aldose reductase (AR) capable of potently blocking the excess glucose flux through the polyol pathway that prevails under diabetic conditions has been a long-standing challenge. In response, we did high-throughput screening of our internal libraries of compounds and identified 6-phenylsulfonylpyridazin-2H-3-one, 8, which showed modest inhibition of AR, both in vitro and in vivo. Initial structure-activity relationships concentrated on phenyl substituents and led to 6-(2,4-dichlorophenylsulfonyl)-2H-pyridazin-3-one, 8l, which was more potent than 8, both in vitro and in vivo. Incorporation of extant literature findings with other aldose reductase inhibitors, including zopolrestat, resulted in the title inhibitor, 19m, which is one of the most potent and highly selective non-carboxylic acid, non-hydantoin inhibitors of AR yet described (IC50, 1 nM; ED90 vs sciatic nerve sorbitol and fructose, respectively, 0.8 and 4.0 mg/kg). In rats, its oral bioavailability is 98% and it has a favorable plasma t(1/2) (26 +/- 3 h).