Structure-activity relationship studies on 1-[2-(4-Phenylphenoxy)ethyl]pyrrolidine (SC-22716), a potent inhibitor of leukotriene A(4) (LTA(4)) hydrolase.

Leukotriene B(4) (LTB(4)) is a pro-inflammatory mediator that has been implicated in the pathogenesis of a number of diseases including inflammatory bowel disease (IBD) and psoriasis. Since the action of LTA(4) hydrolase is the rate-limiting step for LTB(4) production, this enzyme represents an attractive pharmacological target for the suppression of LTB(4) production. From an in-house screening program, SC-22716 (1, 1-[2-(4-phenylphenoxy)ethyl]pyrrolidine) was identified as a potent inhibitor of LTA(4) hydrolase. Structure-activity relationship (SAR) studies around this structural class resulted in the identification of a number of novel, potent inhibitors of LTA(4) hydrolase, several of which demonstrated good oral activity in a mouse ex vivo whole blood assay.

The prostaglandin analogs, misoprostol and SC-46275, potently inhibit cytokine release from activated human monocytes.

Inflammatory mediator release is one of the body's responses to tissue injury and inflammation. These mediators, such as interleukin-1 beta (I1-1 beta), tumor necrosis factor (TNF-alpha), and products of arachidonic acid metabolism, are themselves proinflammatory. Purified human monocytes stimulated in vitro with E. coli-derived lipopolysaccharide (LPS) will release these key cytokines along with various other eicosanoid mediators. Monocytes incubated with LPS and the prostaglandin E-1 analog, misoprostol, released significantly lower levels of cytokines compared to monocytes incubated with LPS alone. Eicosanoid release was also affected by misoprostol. SC-46275, a more potent mucosal protective PGE1 analog, also altered the release of cytokines and eicosanoids from human monocytes. However SC-46275 inhibited I1-1 beta release with an IC50 value of 9 microM compared to 75 microM for misoprostol. SC-46275 and misoprostol both inhibited TNF-alpha release. These data suggest there is a potential immunomodulatory role for prostaglandin analogs in the therapeutic treatment of inflammatory diseases such as ulcerative colitis, Crohn's disease, and autoimmune inflammatory diseases of the central nervous system.

Catalytic functionalization of polymers: a novel approach to site specific delivery of misoprostol to the stomach.

The application of functionalized polymers to site-directed delivery of the antiulcer prostaglandin, misoprostol, is described. By use of homogeneous catalysis, the simple polymer, polybutadiene, was modified to incorporate the specialized requirements for controlled delivery of misoprostol to the stomach. An acid labile silyl ether bond to the C-11 hydroxyl of misoprostol was installed as the primary rate determining step for drug release, and a series of analogs, in which the steric hindrance about the silicon atom was varied, was prepared and evaluated for in vitro release rates, efficacy against indomethacin induced gastric damage and diarrheagenic activity. The diisopropylsilyl analog, the slowest releasing system studied, showed efficacy equal to misoprostol against indomethacin-induced gastric damage and no diarrhea at the highest dose tested.

Mucosal protective activity of prostaglandin analogs in rodent colonic inflammation.

The mucosal protective prostaglandin analogs misoprostol, enisoprost, and SC-46275 (the 17E-18-cyclopentenyl analog of enisoprost) were tested in mouse and rat colitis induced by the intrarectal instillation of dilute acetic acid. Colitis was assessed by histology and colonic levels of myeloperoxidase (a neutrophil marker enzyme). When given as enemas 30 min ahead of colitis induction, 15(R)-15-methyl-PGE2 (arbaprostil) and 15(S)-15-methyl-PGE1 were inactive; however, misoprostol, enisoprost, and SC-46275 protected against colonic inflammation with ED50 values of 24, 12 and 1.3 micrograms/kg, respectively, in rats and 11, 5, and 1 micrograms/kg, respectively, in mice. These compounds may have utility in the medical management of human inflammatory bowel disease.

Characterization of prostaglandin E receptors in canine small intestine using [3H] prostaglandin E1 binding.

Prostaglandin E (PGE) receptors in canine small intestinal mucosal and muscle membrane preparations were labeled with [3H] PGE1. Saturable, high affinity binding of [3H] PGE1 was observed in both preparations. The density of binding sites (fmol/mg protein) was 39 for mucosal membranes and 60 for muscle membranes, with corresponding dissociation constants of 10.6 nM and 5.8 nM, respectively. [3H] PGE1 binding sites in both preparations showed stereospecificity and high affinity for natural PGE1 and PGE2, but not for I or F-type PGs. Synthetic PGEs such as misoprostol and enisoprost had lower affinity than PGE1 or PGE2. Several analogs of enisoprost bound weakly to the binding sites. A highly significant correlation (C.C. = 0.9) was demonstrated between mucosal and muscle binding potency for a series of enisoprost analogs. There was also a significant positive correlation between the receptor binding potency and rat diarrheagenic activity for these analogs. These results indicate that PGE receptors in canine intestinal mucosa and muscle can be directly studied with [3H] PGE1 binding. The mucosal and muscle PGE receptors may have similar ligand binding specificity. We speculate that these receptors are likely to be associated with the diarrheagenic activity of PGEs.

Synthesis and structure-activity relationships of acyclic omega chain conjugated diene analogues of enisoprost.

A series of acyclic omega chain conjugated diene analogues of enisoprost were synthesized and evaluated for gastric antisecretory and diarrheagenic activities in comparison to enisoprost and a previously identified cyclic dienyl analogue. Several novel approaches to the cuprate reagents involved in the synthesis of the series are described. From this SAR study, it appears that both the conjugated diene and the overall space filling characteristics of the omega chain are important components to the pharmacological profiles and selectivity of these compounds and that a cyclic structure is not required.

SC-46275: a potent, long-acting gastric antisecretory prostaglandin with low oral bioavailability in the dog.

The synthetic prostaglandin, SC-46275, an omega chain cyclopentenyl analog of enisoprost, was studied to determine its gastric antisecretory potency and duration of action in meal-stimulated innervated (Pavlov) pouch dogs and its p.o. bioavailability in unoperated fasted dogs. SC-46275 exhibited potent antisecretory activity when administered directly into the gastric pouch, the ED50 being 0.01 micrograms/kg. It had a long duration of antisecretory action; significant (P less than or equal to .05) inhibition of total acid output was observed 16 hr after intrapouch administration of 0.03 micrograms/kg. At this dose p.o., neither SC-46275 nor its free acid metabolite was detected in plasma. These data indicate that SC-46275 has novel properties: it is a potent, long-acting gastric antisecretory agent which is not readily available systemically after p.o. administration. Thus, potential systemic side effects are expected to be absent or minimized at doses of SC-46275 which inhibit gastric acid secretion, and therefore it might be useful in peptic ulcer disease.

Chemistry and structure-activity relationships of C-17 unsaturated 18-cycloalkyl and cycloalkenyl analogues of enisoprost. Identification of a promising new antiulcer prostaglandin.

A series of delta 17 unsaturated cycloalkyl and cycloalkenyl analogues of enisoprost was synthesized to investigate the effects of omega chain unsaturation on gastric antisecretory activity and diarrheogenic side effects. Of these, the 17E, 18-cyclopentenyl analogue 5d displayed potent gastric antisecretory activity in dogs but very weak diarrheogenic properties in rats and is the most selective prostaglandin compound discovered in these laboratories. Structurally, 5d contains both a conjugated diene and tertiary allylic alcohol in the omega chain, and these chemical features impart some interesting oxidative and acid-catalyzed epimerization and allylic rearrangement reactivities, respectively.

18-cycloalkyl analogues of enisoprost.

By use of standard cuprate methodology, a series of 18-cycloalkyl analogues of enisoprost was prepared in an effort to impede omega chain metabolism and prolong duration of gastric antisecretory activity. An initial product of omega chain oxidation, the C-20 hydroxy analogue, was also synthesized for pharmacological comparison. The cyclopropyl, cyclobutyl, and cyclopentyl analogues were approximately one-fourth as potent as enisoprost in inhibiting gastric acid secretion, while the cyclohexyl and cycloheptyl analogues showed very weak activity, and the 20-hydroxy compound was inactive at a dose 100 times the ED50 of enisoprost. The cyclobutyl compound had a longer duration of antisecretory action than enisoprost and the other cycloalkyl analogues. The cycloalkyl analogues unexpectedly possessed low diarrheogenic activity in rats.

Synthesis and gastrointestinal pharmacology of a 3E,5Z diene analogue of misoprostol.

A stereospecific synthesis and the gastric antisecretory and diarrheal activity of a 3E,5Z diene analogue of misoprostol are described. The key intermediate in the synthesis was an alpha chain truncated acetylene that was obtained by a cuprate/enolate capture procedure on the corresponding cyclopentenone. Palladium-catalyzed coupling of the acetylene with methyl 4-iodo-3(E)-butenoate provided the conjugated enyne. Although selective hydrogenation of the enyne with Lindlar catalyst failed, the desired 3E,5Z diene was obtained with P-2 nickel as catalyst. The diene was about 3 times more potent than misoprostol in inhibiting gastric acid secretion in dogs and also in producing diarrhea in rats.

Alpha chain unsaturated derivatives of misoprostol.

Misoprostol, a 15-deoxy-16-hydroxy-16-methyl analog of PGE1, is an effective agent for the treatment of peptic ulcer disease. Efforts to impede metabolic degradation of the alpha chain of misoprostol led to the discovery of a second clinical candidate in this series. Enisoprost, a delta 4Z derivative of misoprostol, is more potent as a gastric antisecretory agent and longer acting than misoprostol. These findings prompted further work to determine the effects that two double bonds in the alpha chain might have on the activity profile of misoprostol. The most promising structure in this series was a 1:1 mixture of 3E,5Z and 3Z,5Z dienes which was about three times more potent than misoprostol in inhibiting gastric secretion in dogs, while the separation of the diarrheogenic effect was significantly improved. Chromatographic separation of the mixture was very difficult, but small amounts of each isomer were obtained by HPLC, and preliminary antisecretory studies indicated that most of the activity resided in the 3E,5Z isomer. A stereospecific synthesis of the 3E,5Z isomer was carried out to provide sufficient quantities for complete pharmacological assessment. The 3E,5Z diene was about three times more potent than misoprostol in inhibiting gastric acid secretion in dogs and also in producing diarrhea in rats.

Synthesis and gastric antisecretory properties of alpha chain diene derivatives of misoprostol.

The synthesis and gastric antisecretory activity in dogs of seven alpha chain diene derivatives of misoprostol are described. The key intermediates in the preparation of these compounds were C-9 tert-butyldimethylsilyl enol ethers that were obtained by in situ silylation of cuprate enolates derived from alpha chain unsaturated cyclopentenones. Selenylation chemistry on these intermediates provided the C2-C3 trans dienes that, where possible, were also deconjugated to produce the corresponding C3-C4 dienes. The most interesting structure in this series is the C5-C6 cis, C3-C4 cis/trans (1:1) diene that could not be readily separated chromatographically into its individual geometric isomers. The gastric antisecretory activity of the mixture of isomers was approximately 3 times greater than that of misoprostol by intragastric administration. The separation of undesired diarrheogenic effects from antisecretory activity was significantly improved relative to misoprostol.

Synthesis and gastric antisecretory properties of 4,5-unsaturated derivatives of 15-deoxy-16-hydroxy-16-methylprostaglandin E1.

The synthesis and gastric antisecretory activities of the delta 4,5-cis, delta 4,5-trans, and 4,5-acetylenic analogues of 15-deoxy-16-hydroxy-16-methyl prostaglandin E1 methyl ester are described. The key step in the preparation of these compounds involved the stereospecific conjugate addition of a cuprate reagent to the appropriate cyclopentenones. Although the trans and acetylenic derivatives were weak inhibitors of gastric acid secretion, the cis olefin was more potent and longer acting than the saturated parent compound. Selectivity with respect to unwanted diarrheagenic effects was found to be improved over that of both the parent 16-hydroxy compound and the reference standards, (15S)-15-methyl- and 16,16-dimethylprostaglandin E2.