THIOPYRANO[2,3,4-CD]INDOLES AS 5-LIPOXYGENASE INHIBITORS - SYNTHESIS, BIOLOGICAL PROFILE, AND RESOLUTION OF 2-[2-[1-(4-CHLOROBENZYL)-4-METHYL-6-[(5-PHENYLPYRIDIN-2-YL)METHOXY]-4,5-DIHYDRO-1H-THIOPYRANO[2,3,4-CD]INDOL-YL]ETHOXY]BUTANOIC ACID

Leukotriene biosynthesis inhibitors have potential as new therapies for asthma and inflammatory diseases. The recently disclosed thiopyrano[2,3,4-cd] indole class of 5-lipoxygenase (5-LO) inhibitors has been investigated with particular emphasis on the side chain bearing the acidic functionality. The SAR studies have shown that the inclusion of a heteroatom (O or S) in conjunction with an alpha-ethyl substituted acid leads to inhibitors of improved potency. The most potent inhibitor prepared contains a 2-ethoxybutanoic acid side chain. This compound, 14d (2-[2-[1-(4-chlorobenzyl)-4-methyl-6-[ (5-phenylpyridin-2-yl)methoxy]-4,5-dihydro-1H-thiopyrano[2,3,4-cd]indol-2-yl]ethoxy]-butanoic acid, L-699,333), inhibits 5-HPETE production by human 5-LO and LTB(4) biosynthesis by human PMN leukocytes and human whole blood (IC(50)s Of 22 nM, 7 nM and 3.8 mu M, respectively). The racemic acid 14d has been shown to be functionally active in a rat pleurisy model (inhibition of LTB(4), ED(50) = 0.65 mg/kg, 6 h pretreatment) and in the hyperreactive rat model of antigen-induced dyspnea(50% inhibition at 2 and 4 h pretreatment; 0.5 mg/kg po). In addition, 14d shows excellent functional activity against antigen-induced bronchoconstriction in the conscious squirrel monkey [89% inhibition of the increase in R(L) and 68% inhibition in the decrease in C-dyn (0.1 mg/kg, n = 3)] and in the conscious sheep models of asthma (iv infusion at 2.5 mu g/kg/min). Acid 14d is highly selective as an inhibitor of 5-LO activity when compared to the inhibition of human 15-LO, porcine 12-LO and ram seminal vesicle cyclooxygenase (IC50 > 5 mu M) Or competition in a FLAP binding assay (IC5O > 10 mu M). Resolution of 14d affords 14g, the most potent diastereomer, which inhibits the 5-HPETE production of human 5-LO and LTB(4) biosynthesis of human PMN leukocytes and human whole blood with IC(50)s Of 8 nM, 4 nM, and 1 mu M respectively. The in vitro and in vivo profile of 14d is comparable to that of MK-0591, which has showed biochemical efficacy in inhibiting ex vivo LTB(4) biosynthesis and urinary LTE(4) excretion in clinical trials.