John E. Bishop

Identification and characterization of the ocular hypotensive efficacy of travoprost, a potent and selective FP prostaglandin receptor agonist, and AL-6598, a DP prostaglandin receptor agonist

The structure-activity studies that led to the identification of travoprost, a highly selective and potent FP prostaglandin analog, and AL-6598, a DP prostaglandin analog, are detailed. In both series, the 1-alcohol analogs are very effective and are thought to be acting as prodrugs for the biologically active carboxylic acids. The efficacy of amide prodrugs depends on the degree of substitution and the size of the substituents. Selected compounds are profiled in vitro and in vivo preclinically. Clinical studies show that travoprost 0.004% (isopropyl ester) provided intraocular pressure control superior to timolol 0.5% when used as monotherapy in patients with open-angle glaucoma or ocular hypertension. In clinical studies, AL-6598 0.01% provided a sustained intraocular pressure reduction with q.d. application; b.i.d. provided greater intraocular pressure control. The acute and, apparently, conjunctival hyperemia associated with topical ocular AL-6598 can be attenuated while maintaining intraocular pressure-lowering efficacy by formulating with brimonidine.

3-Oxa-15-cyclohexyl Prostaglandin DP Receptor Agonists as Topical Antiglaucoma Agents

A series of prostaglandin DP agonists containing a 3-oxa-15-cyclohexyl motif was synthesized and evaluated in several in vitro and in vivo biological assays. The reference compound ZK 118.182 (9beta-chloro-15-cyclohexyl-3-oxa-omega-pentanor PGF(2alpha)) is a potent full agonist at the prostaglandin DP receptor. Saturation of the 13,14 olefin affords AL-6556, which is less potent but is still a full agonist. Replacement of the 9-chlorine with a hydrogen atom or inversion of the carbon 15 stereochemistry also reduces affinity. In in vivo studies ZK 118.182 lowers intraocular pressure (IOP) upon topical application in the ocular hypertensive monkey. Ester, 1-alcohol, and selected amide prodrugs of the carboxylic acid enhance in vivo potency, presumably by increasing bioavailability. The clinical candidate AL-6598, the isopropyl ester prodrug of AL-6556, produces a maximum 53% drop in monkey IOP with a 1 microg dose (0.003% w/w) using a twice-daily dosing regime. Synthetically, AL-6598 was accessed from known intermediate 1 using a novel key sequence to install the cis allyl ether in the alpha chain, involving a selective Swern oxidative desilylation of a primary silyl ether in the presence of a secondary silyl ether. In this manner, 136 g of AL-6598 was synthesized under GMP conditions for evaluation in phase I clinical trials.