X-ray crystallographic and kinetic studies of human sorbitol dehydrogenase.

Sorbitol dehydrogenase (hSDH) and aldose reductase form the polyol pathway that interconverts glucose and fructose. Redox changes from overproduction of the coenzyme NADH by SDH may play a role in diabetes-induced dysfunction in sensitive tissues, making SDH a therapeutic target for diabetic complications. We have purified and determined the crystal structures of human SDH alone, SDH with NAD(+), and SDH with NADH and an inhibitor that is competitive with fructose. hSDH is a tetramer of identical, catalytically active subunits. In the apo and NAD(+) complex, the catalytic zinc is coordinated by His69, Cys44, Glu70, and a water molecule. The inhibitor coordinates the zinc through an oxygen and a nitrogen atom with the concomitant dissociation of Glu70. The inhibitor forms hydrophobic interactions to NADH and likely sterically occludes substrate binding. The structure of the inhibitor complex provides a framework for developing more potent inhibitors of hSDH.

A novel series of non-carboxylic acid, non-hydantoin inhibitors of aldose reductase with potent oral activity in diabetic rat models: 6-(5-chloro-3-methylbenzofuran-2-sulfonyl)-2H-pyridazin-3-one and congeners.

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).

A sorbitol dehydrogenase inhibitor of exceptional in vivo potency with a long duration of action: 1-(R)-[4-[4-(4,6-dimethyl[1,3,5]triazin-2-yl)- 2R,6S-dimethylpiperazin-1-yl]pyrimidin-2- yl]ethanol.

We report here a novel sorbitol dehydrogenase inhibitor, 16, that shows very high oral potency (50 microg/kg) in normalizing elevated fructose levels in the sciatic nerve of chronically diabetic rats and sustained duration of action (>24 h). Furthermore, 16 shows attractive pharmaceutical properties, including good solubility in simulated human gastric fluid, excellent Caco-2 Papp, moderate lipophilicity, and metabolic stability for achieving good oral absorption and long duration of action.

Orally-effective, long-acting sorbitol dehydrogenase inhibitors: synthesis, structure-activity relationships, and in vivo evaluations of novel heterocycle-substituted piperazino-pyrimidines.

Optimization of a previously disclosed sorbitol dehydrogenase inhibitor (SDI, II) for potency and duration of action was achieved by replacing the metabolically labile N,N-dimethylsulfamoyl group with a variety of heterocycles. Specifically, this effort led to a series of novel, in vitro potent SDIs with longer serum half-lives and acceptable in vivo activity in acutely diabetic rats (e.g., 62, 67, and 69). However, the desired in vivo potency in chronically diabetic rats, ED(90) < or = 5 mg/kg/day, was achieved only through further modification of the piperazine linker. Several members of this family, including 86, showed better than the targeted potency with ED(90) values of 1-2 mg/kg/day. Compound 86 was further profiled and found to be a selective inhibitor of sorbitol dehydrogenase, with excellent pharmacodynamic/pharmacokinetic properties, demonstrating normalization of sciatic nerve fructose in a chronically diabetic rat model for approximately 17 h, when administered orally at a single dose of 2 mg/kg/day.

A highly selective, non-hydantoin, non-carboxylic acid inhibitor of aldose reductase with potent oral activity in diabetic rat models: 6-(5-chloro-3-methylbenzofuran- 2-sulfonyl)-2-H-pyridazin-3-one.

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).

Early neural and vascular dysfunctions in diabetic rats are largely sequelae of increased sorbitol oxidation.

These experiments were undertaken to assess the importance of cytoplasmic (c) sorbitol oxidation versus mitochondrial (m) pyruvate oxidation in mediating neural and vascular dysfunction attributable to hyperglycemia in diabetic rats. Increased oxidation of sorbitol is coupled to enzymatic reduction of free oxidized NAD(+)c to reduced NADHc, manifested by an increased ratio of NADH to NAD(+)c. Likewise, increased oxidation of pyruvate is coupled to reduction of NAD(+)m to NADHm, which increases the NADH/NAD(+)m ratio. Specific inhibitors of sorbitol production or sorbitol oxidation normalized: increased diabetic nerve NADH/NAD(+)c, impaired nerve-conduction velocity, and vascular dysfunction in sciatic nerve, retina, and aorta; however, they had little or no impact on increased NADH/NAD(+)m. These observations provide, for the first time, strong in vivo evidence for the primacy of sorbitol oxidation versus. pyruvate oxidation in mediating the metabolic imbalances, impaired nerve conduction, and vascular dysfunction evoked by diabetes. These findings are consistent with (a) the fact that oxidation of sorbitol produces "prooxidant" NADHc uncoupled from subsequent production of "antioxidant" pyruvate required for reoxidation of NADHc to NAD(+)c by lactate dehydrogenase, and (b) the hypothesis that neural and vascular dysfunction in early diabetes are caused primarily by increased NADHc, which fuels superoxide production by NADH-driven oxidases.

Design and synthesis of a novel family of triazine-based inhibitors of sorbitol dehydrogenase with oral activity: 1-[4-[3R,5S-dimethyl-4-(4-methyl-[1,3,5]triazin-2-yl)-piperazin-1-yl]-[1,3,5]triazin-2-yl]-(R) ethanol.

Two new templates, (R) 2-hydroxyethyl-pyridine and (R) 2-hydroxyethyl-triazine, were used to design novel sorbitol dehydrogenase inhibitors (SDIs). The design concept included spawning of these templates to function as effective ligands to the catalytic zinc within the enzyme through incorporation of optimally substituted piperazino-triazine side chains so as to accommodate the active site in the enzyme for efficient binding. This strategy resulted in orally active SDIs, which penetrate key tissues, for example, sciatic nerve of chronically diabetic rats. The latter template led to the design of the title inhibitor, 33, which normalized the elevated sciatic nerve fructose by 96% at an oral dose of 10mg/kg.