Design and synthesis of water soluble β-aminosulfone analogues of SCH 900229 as γ-secretase inhibitors

In this paper we describe our strategy to improve the aqueous solubility of SCH 900229, a potent PS1-selective γ-secretase inhibitor for the treatment of Alzheimer's disease. Incorporation of ionizable amino groups into the side chain terminal generates water soluble β-aminosulfone analogues of SCH 900229 that maintain robust in vitro potency and in vivo efficacy.

A-ring modification of SCH 900229 and related chromene sulfone γ-secretase inhibitors

Attempts to block metabolism by incorporating a 9-fluoro substituent at the A-ring of compound 1 (SCH 900229) using electrophilic Selectfluor™ led to an unexpected oxidation of the A-ring to give difluoroquinone analog 1a. Oxidation of other related chromene γ-secretase inhibitors 2-8 resulted in similar difluoroquinone analogs 2a-8a, respectively. These quinone products exhibited comparable in vitro potency in a γ-scretase membrane assay, but were several fold less potent in a cell-based assay in lowering Aβ40-42, compared to their parent compounds.

Discovery of SCH 900229, a Potent Presenilin 1 Selective γ-Secretase Inhibitor for the Treatment of Alzheimer's Disease

An exploration of the SAR of the side chain of a novel tricyclic series of γ-secretase inhibitors led to the identification of compound (-)-16 (SCH 900229), which is a potent and PS1 selective inhibitor of γ-secretase (Aβ40 IC50 = 1.3 nM). Compound (-)-16 demonstrated excellent lowering of Aβ after oral administration in preclinical animal models and was advanced to human clinical trials for further development as a therapeutic agent for the treatment of Alzheimer's disease.

Synthesis and SAR Studies of Fused Oxadiazines as γ-Secretase Modulators for Treatment of Alzheimer's Disease

Fused oxadiazines (3) were discovered as selective and orally bioavailable γ-secretase modulators (GSMs) based on the structural framework of oxadiazoline GSMs. Although structurally related, initial modifications showed that structure-activity relationships (SARs) did not translate from the oxadiazoline to the oxadiazine series. Subsequent SAR studies on modifications at the C3 and C4 positions of the fused oxadiazine core helped to identify GSMs such as compounds 8r and 8s that were highly efficacious in vitro and in vivo in a number of animal models with highly desirable physical and pharmacological properties. Further improvements of in vitro activity and selectivity were achieved by the preparation of fused morpholine oxadiazines. The shift in specificity of APP cleavage rather than a reduction in overall γ-secretase activity and the lack of changes in substrate accumulation and Notch processing as observed in the animal studies of compound 8s confirm that the oxadiazine series of compounds are potent GSMs.

Identification of presenilin 1-selective γ-secretase inhibitors with reconstituted γ-secretase complexes

Accumulation of the β-amyloid (Aβ) peptides is one of the major pathologic hallmarks in the brains of Alzheimer's disease (AD) patients. Aβ is generated by sequential proteolytic cleavage of the amyloid precursor protein (APP) catalyzed by β- and γ-secretases. Inhibition of Aβ production by γ-secretase inhibitors (GSIs) is thus being pursued as a target for treatment of AD. In addition to processing APP, γ-secretase also catalyzes proteolytic cleavage of other transmembrane substrates, with the best characterized one being the cell surface receptor Notch. GSIs reduce Aβ production in animals and humans but also cause significant side effects because of the inhibition of Notch processing. The development of GSIs that reduce Aβ production and have less Notch-mediated side effect liability is therefore an important goal. γ-Secretase is a large membrane protein complex with four components, two of which have multiple isoforms: presenilin (PS1 or PS2), aph-1 (aph-1a or aph-1b), nicastrin, and pen-2. Here we describe the reconstitution of four γ-secretase complexes in Sf9 cells containing PS1--aph-1a, PS1--aph-1b, PS2--aph-1a, and PS2--aph-1b complexes. While PS1--aph-1a, PS1--aph-1b, and PS2--aph-1a complexes displayed robust γ-secretase activity, the reconstituted PS2--aph-1b complex was devoid of detectable γ-secretase activity. γ-Secretase complexes containing PS1 produced a higher proportion of the toxic species Aβ42 than γ-secretase complexes containing PS2. Using the reconstitution system, we identified MRK-560 and SCH 1500022 as highly selective inhibitors of PS1 γ-secretase activity. These findings may provide important insights into developing a new generation of γ-secretase inhibitors with improved side effect profiles.

Effects of a selective melanin-concentrating hormone 1 receptor antagonist on food intake and energy homeostasis in diet-induced obese mice

Melanin concentrating hormone (MCH) is a cyclic neuropeptide expressed in the lateral hypothalamus that plays an important role in energy homeostasis. To investigate the pharmacological consequences of inhibiting MCH signaling in murine obesity models, we examined the effect of acute and chronic administration of a selective MCH1 receptor antagonist (SCH-A) in diet-induced obese (DIO) and Lep(ob/ob) mice. Oral administration of SCH-A for 5 consecutive days (30 mg/kg q.d.) produced hypophagia, a loss of body weight and adiposity, and decreased plasma leptin levels in DIO mice, and hypophagia and reduced weight gain in Lep(ob/ob) mice. Chronic administration of SCH-A to DIO mice decreased food intake, body weight and adiposity, and plasma leptin and free fatty acids. These effects were accompanied by increases in several hypothalamic neuropeptides. Acute administration of SCH-A (30 mg/kg) prevented the decrease in energy expenditure associated with food restriction. These results indicate that MCH1 receptor antagonists may be effective in the treatment of obesity.

Improving the oral efficacy of CNS drug candidates: discovery of highly orally efficacious piperidinyl piperidine M2 muscarinic receptor antagonists

In search of a backup M(2) muscarinic receptor antagonist to the previously reported compound 1, we discovered compound (+)-14, which showed superior oral efficacy in animal models. The improvement of oral efficacy was achieved by modulating both the molecular weight and lipophilicity of the lead compounds.

Facilitation of acetylcholine release and improvement in cognition by a selective M2 muscarinic antagonist, SCH 72788

Current treatment of Alzheimer's Disease (AD) requires acetylcholinesterase inhibition to increase acetylcholine (ACh) concentrations in the synaptic cleft. Another mechanism by which ACh levels can be increased is blockade of presynaptic M2 muscarinic autoreceptors that regulate ACh release. An antagonist designed for this purpose must be highly selective for M2 receptors to avoid blocking postsynaptic M1 receptors, which mediate the cognitive effects of ACh. Structure-activity studies of substituted methylpiperadines led to the synthesis of 4-[4-[1(S)-[4-[(1,3-benzodioxol-5-yl)sulfonyl]phenyl]ethyl]-3(R)-methyl-1-piperazinyl]-4-methyl-1-(propylsulfonyl)piperidine. This compound, SCH 72788, binds to cloned human M2 receptors expressed in CHO cells with an affinity of 0.5 nM, and its affinity at M1 receptors is 84-fold lower. SCH 72788 is a functional M2 antagonist that competitively inhibits the ability of the agonist oxotremorine-M to inhibit adenylyl cyclase activity. In an in vivo microdialysis paradigm, SCH 72788 increases ACh release from the striatum of conscious rats. The compound is also active in a rodent model of cognition, the young rat passive avoidance response paradigm. The effects of SCH 72788 suggest that M2 receptor antagonists may be useful for treating the cognitive decline observed in AD and other dementias.

Muscarinic agonists and antagonists in the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive impairment and personality changes. The development of drugs for the treatment of the cognitive deficits of AD has focused on agents which counteract loss in cholinergic activity. Although symptoms of AD have been successfully treated with acetylcholinesterase inhibitors (tacrine, donepezil. rivastigmine, galanthamine), limited success has been achieved with direct M1 agonists, probably due to their lack of selectivity versus other muscarinic receptor subtypes. Muscarinic M2 antagonists have been reported to increase synaptic levels of acetylcholine after oral administration to rats (e.g. BIBN-99, SCH-57790), but their selectivity versus other muscarinic receptor subtypes is modest. Exploration of a series of piperidinylpiperidines has yielded the potent and selective M2 antagonist SCH-217443. This antagonist has excellent bioavailability in rats and dogs and shows activity in a rat model of cognition.

SCH 57790: a novel M2 receptor selective antagonist

As a decrease in cholinergic neurons has been observed in Alzheimer's Disease (AD), therapeutic approaches to AD include inhibition of acetylcholinesterase to increase acetylcholine levels. Evidence suggests that acetylcholine release in the CNS is modulated by negative feedback via presynaptic M2 receptors, blockade of which should provide another means of increasing acetylcholine release. Structure-activity studies of [4-(phenylsulfonyl)phenyl]methylpiperazines led to the synthesis of 4-cyclohexyl-alpha-[4-[[4-methoxyphenyl]sulfinyl]-phenyl]-1-piperazin eacetonitrile. This compound, SCH 57790, binds to cloned human M2 receptors expressed in CHO cells with an affinity of 2.78 nM; the affinity at M1 receptors is 40-fold lower. SCH 57790 is an antagonist at M2 receptors expressed in CHO cells, as the compound blocks the inhibition of adenylyl cyclase activity mediated by the muscarinic agonist oxotremorine. This compound should be useful in assessing the potential of M2 receptor blockade for enhancement of cognition.

Inhibitors of acyl CoA:cholesterol acyltransferase

Conformational restriction of previously disclosed acyclic (diphenylethyl)diphenylacetamides led to the discovery of several potent inhibitors of acyl CoA:cholesterol acyltransferase (ACAT). cis-[2-(4-Hydroxyphenyl)-1-indanyl]diphenylacetamide (4a) was the most potent ACAT inhibitor identified (IC50 = 0.04 microM in an in vitro rat hepatic microsomal ACAT assay, ED50 = 0.72 mg/kg/day in cholesterol-fed hamster.