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.

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).