Sorbitol dehydrogenase inhibitors (SDIs): a new potent, enantiomeric SDI, 4-[2-1R-hydroxy-ethyl)-pyrimidin-4-yl]piperazine-1-sulfonic acid dimethylamide.

We report here on our medicinal chemistry and pharmacology efforts to provide a potent sorbitol dehydrogenase inhibitor (SDI) as a tool to probe a recently disclosed hypothesis centered on the role of sorbitol dehydrogenase (SDH) in the second step of the polyol pathway, under conditions of high glucose flux. Starting from a weak literature lead, 2, and through newly developed structure-activity relationships, we have designed and executed an unambiguous synthesis of enantiomeric SDI, 6, which is at least 10x more potent than 2. Also, 6 potently inhibits SDH in streptozotocin-diabetic rat sciatic nerve. We have described an expedient synthesis of a key building template, 33, for future research in the SDI area that may facilitate the discovery of even more potent SDIs with longer duration of action in vivo.

Orally active aldose reductase inhibitors: indazoleacetic, oxopyridazineacetic, and oxopyridopyridazineacetic acid derivatives.

Benzothiazole side chains featured in zopolrestat (1a) and its congeners were incorporated into oxophthalazineacetic acid replacements, including indazole, pyridazinone, and pyridopyridazinone with a pendant acetic acid moiety. Potent aldose reductase inhibition activity among resulting compounds is as widespread as it is in the earlier zopolrestat series, thus lending further support to our hypothesis that there is a binding site on the aldose reductase enzyme with strong affinity for benzothiazoles. Representative new compounds 1-[(5,7-difluoro-2-benzothiazolyl)-methyl]-1H-indazoleacetic acid (62), [6-[[5-(trifluoromethyl)benzothiazol-2-yl]methyl]-8-oxo- 6H-pyrido[2,3-d]-pyridazin-5-yl]acetic acid (70), 3,4-dihydro-4-oxo-5,6-dimethyl-3-[(5,7-difluorobenzothiazol-2-yl) methyl]-1-pyridazineacetic acid (79), and 3,4-dihydro-4-oxo-5,6-cyclohexano-3-[[5-(trifluoromethyl) benzothiazol-2-yl]-methyl]-1-pyridazineacetic acid (82) are potent aldose reductase inhibitors with IC50s of 30, 2.1, 5, and 52.2 nM, respectively. The best of these compounds, 79 and 82, also inhibit accumulation of sorbitol in rat sciatic nerve in a model of diabetic complications, when administered orally at 10 mg/kg. The inhibition values are 76 and 61%, respectively. In addition to benzothiazole, we have examined its surrogates effective in potentiating aldose reductase inhibition activity, including benzoxazole and aryl[1,2,4]oxadiazole. Structure-activity relationships emerging from this program are also discussed.

Potent, orally active aldose reductase inhibitors related to zopolrestat: surrogates for benzothiazole side chain.

A broad structure-activity program was undertaken in search of effective surrogates for the key benzothiazole side chain of the potent aldose reductase inhibitor, zopolrestat (1). A structure-driven approach was pursued, which spanned exploration of three areas: (1) 5/6 fused heterocycles such as benzoxazole, benzothiophene, benzofuran, and imidazopyridine; (2) 5-membered heterocycles, including oxadiazole, oxazole, thiazole, and thiadiazole, with pendant aryl groups, and (3) thioanilide as a formal equivalent of benzothiazole. Several benzoxazole- and 1,2,4-oxadiazole-derived analogues were found to be potent inhibitors of aldose reductase from human placenta and were orally active in preventing sorbitol accumulation in rat sciatic nerve, in an acute test of diabetic complications. 3,4-Dihydro-4-oxo-3-[(5,7-difluoro-2-benzoxazolyl)methyl]-1- phthalazineacetic acid (124) was the best of the benzoxazole series (IC50 = 3.2 x 10(-9) M); it suppressed accumulation of sorbitol in rat sciatic nerve by 78% at an oral dose of 10 mg/kg. Compound 139, 3,4-dihydro-4-oxo-3-[[(2-fluorophenyl)-1,2,4- oxadiazol-5-yl]methyl]-1-phthalazineacetic acid, with IC50 less than 1.0 x 10(-8) M, caused a 69% reduction in sorbitol accumulation in rat sciatic nerve at an oral dose of 25 mg/kg. The thioanilide side chain featured in 3-[2-[[3-(trifluoromethyl)phenyl]amino]-2-thioxoethyl]-3,4-dihydro - 4-oxo-1-phthalazineacetic acid (195) proved to be an effective surrogate for benzothiazole. Compound 195 was highly potent in vitro (IC50 = 5.2 x 10(-8) M) but did not show oral activity when tested at 100 mg/kg. Additional structure-activity relationships encompassing a variety of heterocyclic side chains are discussed.

A highly specific aldose reductase inhibitor, ethyl 1-benzyl-3-hydroxy-2(5H)-oxopyrrole-4-carboxylate, and its congeners.

Ethyl 1-benzyl-3-hydroxy-2(5H)-oxopyrrole-4-carboxylate (1, EBPC) is a potent and specific inhibitor of aldose reductase. It was greater than 4000X more potent in its inhibition of rat lens aldose reductase than the closely related rat or pig kidney aldehyde reductase, thus making it the most selective inhibitor of a NADPH-dependent carbonyl reductase identified to date. In agreement with this observation, it was found to be a highly potent inhibitor of aldose reductase from rat sciatic nerve with greater than 98% inhibition at 1 microM, but it was practically devoid of activity against aldehyde reductases from rat liver and brain. Inhibition of aldose reductase was mixed type for glyceraldehyde (Ki = 8.0 x 10(-8) M) and noncompetitive for NADPH (Ki = 1.70 x 10(-8) M). Its potential as an in vitro tool to quantitate monomeric aldo/keto reductase activities in crude tissue extracts is presented. Structure-activity relationships emerging from synthetic modifications of EBPC are discussed. Several modifications were found to be active in vitro against aldose reductase from human placenta and in vivo in a rat model of diabetic complications, but none was more potent than EBPC.

Novel, potent aldose reductase inhibitors: 3,4-dihydro-4-oxo-3-[[5-(trifluoromethyl)-2-benzothiazolyl] methyl]-1-phthalazineacetic acid (zopolrestat) and congeners.

A new working hypothesis that there is a hitherto unrecognized binding site on the aldose reductase (AR) enzyme with strong affinity for benzothiazoles was pursued for the design of novel, potent aldose reductase inhibitors (ARIs). The first application of this hypothesis led to a novel series of 3,4-dihydro-4-oxo-3-(benzothiazolylmethyl)-1-phthalazineacetic+ + + acids. The parent of this series (207) was a potent inhibitor of AR from human placenta (IC50 = 1.9 x 10(-8) M) and was orally active in preventing sorbitol accumulation in rat sciatic nerve, in an acute test of diabetic complications (ED50 = 18.5 mg/kg). Optimization of this lead through medicinal chemical rationale, including analogy from other drug series, led to more potent congeners of 207 and culminated in the design of 3,4-dihydro-4-oxo-3-[[5-(trifluoromethyl)-2-benzothiazolyl] methyl]-1-phthalazineacetic acid (216, CP-73,850, zopolrestat). Zopolrestat was found to be more potent than 207, both in vitro and in vivo. Its IC50 against AR and ED50 in the acute test were 3.1 x 10(-9)M and 3.6 mg/kg, respectively. Its ED50s in reversing already elevated sorbitol accumulation in rat sciatic nerve, retina, and lens in a chronic test were 1.9, 17.6, and 18.4 mg/kg, respectively. It was well absorbed in diabetic patients, resulting in high blood level, showed a highly favorable plasma half-life (27.5 h), and is undergoing further clinical evaluation. An assortment of synthetic methods used for the construction of benzothiazoles, including an efficient synthesis of zopolrestat, is described. Structure-activity relationships in the new series are discussed.

1,2-Dihydro-1-oxopyrrolo[3,2,1-kl]phenothiazine-2-carboxamides and congeners, dual cyclooxygenase/5-lipoxygenase inhibitors with antiinflammatory activity.

A series of 1,2-dihydro-1-oxopyrrolo[3,2,1-kl]phenothiazine, 1,2-dihydro-1-oxopyrrolo[3,2,1-kl]phenoxazine, and 1,2-dihydro-1-oxopyrrolo[3,2,1-de]acridine-2-carboxamides were prepared by reaction of 1,2-dihydro-1-oxo-pyrrolo[3,2,1-kl]phenothiazine or other corresponding phenoxazine and acridan ethyl or methyl esters with appropriate amines. Several members of this family were found to be potent, dual inhibitors of cyclooxygenase and 5-lipoxygenase pathways of arachidonic acid metabolism and to have in vivo antiinflammatory activity in the rat foot edema assay. Structure-activity relationships within this family of compounds are described. 1,2-Dihydro-N-(2-thiazolyl)-1-oxopyrrolo[3,2,1-kl]phenothiazine-1- carboxamide (34) was found to be one of the best compounds to display potent cyclooxygenase/5-lipoxygenase inhibition of arachidonic acid metabolism. Its IC50s against the enzymes sourced from rat basophillic leukemia-1 (RBL-1) cells were 0.07 and 1.4 microM, respectively. It was active in the rat foot edema test for antiinflammatory effect (48% inhibition at 33 mg/kg po) and in the mouse phenylbenzoquinone induced writhing test for analgesic effect (93% inhibition at 32 mg/kg po).

Lipophilic 1,3-xylyl-21-crown-6 macrocyclic polyether 2-carboxylic acids as biological mimics of the ionophore antibiotics.

Twelve lipophilic 1,3-xylyl-21-crown-6 macrocyclic polyether 2-carboxylic acids, two lariat ether 1,3-xylyl-21-crown-6 macrocyclic polyether 2-carboxylic acids, and two 1,3-xylyl-28-crown-8 macrocyclic polyether 2-carboxylic acids were synthesized and tested for in vitro antibacterial activity, in vitro stimulation of rumen propionic acid production, and in vivo anticoccidial activity in chickens. These are biological screens relevant to animal health areas where the ionophore antibiotics such as monensin have found application. While the parent structure 1 without lipophilic substituents was biologically inactive, the lipophilic macrocycles were active in the two in vitro tests but not against chicken coccidiosis. One compound was tested in cattle and was found to increase levels of propionic acid in the rumen fermentation. This effect is considered an important factor for increasing the efficiency of feed utilization in cattle exhibited by the ionophore antibiotic monensin. The alkali ion salts of these lipophilic macrocyclic polyether carboxylic acids are very soluble in organic solvents and insoluble in water. These compounds are proposed to act as ion-transport agents and functional mimics of the ionophore antibiotics in the biological systems described above.

Anticoccidial derivatives of 6-azauracil. 5. Potentiation by benzophenone side chains.

Attachment of p-benzophenone side chains at N1 was found to be one of the most effective modifications for enhancing the potency of 6-azauracil against a broad spectrum of coccidia in chickens. Compound 20 was about 1000-fold more potent than 6-azauracil. Structure-activity relationships paralleled those found in a previously reported series of related analogues containing diphenyl sulfide and sulfone side chains. Drug metabolism studies showed the ketones to be reduced rapidly to carbinols, which are the prevalent species in vivo.

Anticoccidial derivatives of 6-azauracil. 4. A 1000-fold enhancement of potency by phenyl sulfide and phenyl sulfone side chains.

We report further progress in exploiting our earlier discovery that the anticoccidial activity of 6-azauracil increases markedly when appropriately substituted benzyl or phenyl groups are attached at N-1. With guidance from previous structure-activity relationships and a multiple linear regression analysis, 6-azauracils containing phenyl sulfone or phenyl sulfide side chains were prepared. These prevented a broad spectrum of coccidial infections in chickens at minimum inhibitory concentrations by weight in feed as low as 0.25 ppm, a 4000-fold increase in potency over 6-azauracil, and had shorter plasma half-lives than earlier potent analogues. Sulfides were more potent than sulfones, although they were oxidized rapidly to sulfones in vivo.

Anticoccidial derivatives of 6-azauracil. 3. Synthesis, high activity, and short plasma half-life of 1-phenyl-6-azauracils containing sulfonamide substituents.

A series of 1-phenyl-6-azauracils containing sulfonamide substituents was prepared. In contrast to previous 1-phenyl-6-azauracils, some of these sulfonamides combine high activity against Eimeria tenella infections in chickens with a very rapid rate of clearance from plasma. Most active was 1-[3'-chloro-5'-methyl-4'-(morpholinylsulfonyl)phenyl]-6-azauracil, with a minimum effective concentration in feed of about 10 ppm.

Anticoccidial derivatives of 6-azauracil. 2. High potency and long plasma life of N1-phenyl structures.

Attachment of substituted phenyl side chains at N1 of 6-azauracil caused striking increases in plasma life and anticoccidial potency. The increases were related in part to the acidity of the imide hydrogen. Maximum effects were shown by phenyl rings substituted in both meta positions by compact, electron-withdrawing, lipophilic substituents, as in 1-(3',5'-dichlorophenyl)-6-azauracil, which had plasma half-life of 160 h and a potency 250-fold greater than that of 6-azauracil.

Anticoccidial derivatives of 6-azauracil. 1. Enhancement of activity by benzylation of nitrogen-1. Observations on the design of nucleotide analogues in chemotherapy.

Benzylation of 6-azauracil at N-1 (which corresponds to the point of attachment of the ribose phosphate unit in pyrimidine nucleotides) has been found to augment its anticoccidial activity fourfold. The high potency of 1-benzyl-6-azauracil is ascribed to a combination of intrinsic activity, efficient oral absorption, and a moderate rate of excretion. Metabolism experiments using 1-benzyl-6-azauracil labeled with 14C in the heterocycle and (separately) in the side chain showed that, in the drug accounted for, no cleavage had occurred. Additional activity increases were achieved by introducing small, electron-withdrawing substituents in the meta and/or para position(s) of the benzyl group. One of the most active derivaties, 1-(3-cyanobenzyl)-6-azauracil, is about 16 times as potent as 6-azauracil.