Design and synthesis of water soluble ß-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 ß-aminosulfone analogues of SCH 900229 that maintain robust in vitro potency and in vivo efficacy.

Scaffold-hopping from xanthines to tricyclic guanines: A case study of dipeptidyl peptidase 4 (DPP4) inhibitors.

Molecular modeling of unbound tricyclic guanine scaffolds indicated that they can serve as effective bioisosteric replacements of xanthines. This notion was further confirmed by a combination of X-ray crystallography and SAR studies, indicating that tricyclic guanine DPP4 inhibitors mimic the binding mode of xanthine inhibitors, exemplified by linagliptin. Realization of the bioisosteric relationship between these scaffolds potentially will lead to a wider application of cyclic guanines as xanthine replacements in drug discovery programs for a variety of biological targets. Newly designed DPP4 inhibitors achieved sub-nanomolar potency range and demonstrated oral activity in vivo in mouse glucose tolerance test.

Substituted 4-morpholine N-arylsulfonamides as γ-secretase inhibitors.

The design, synthesis, SAR, and biological profile of a substituted 4-morpholine sulfonamide series of γ-secretase inhibitors (GSIs) were described. In several cases, the resulting series of GSIs reduced CYP liabilities and improved γ-secretase inhibition activity compared to our previous research series. Selected compounds demonstrated significant reduction of amyloid-ß (Aß) after acute oral dosing in a transgenic animal model of Alzheimer's disease (AD).

Discovery of a Novel, Potent Spirocyclic Series of γ-Secretase Inhibitors.

In the present paper, we described the design, synthesis, SAR, and biological profile of a novel spirocyclic sulfone series of γ-secretase inhibitors (GSIs) related to MRK-560. We utilized an additional spirocyclic ring system to stabilize the active chair conformation of the parent γ-secretase inhibitors. The resulting series is devoid of the CYP2C9 inhibition liability of MRK-560. A few representative analogs were assessed in a nontransgenic animal model of Alzheimer's disease (AD), demonstrating reduction of amyloid-ß (Aß) in the CNS after acute oral dosing. A spirocyclic phosphonate was identified as the optimal ring system for both potency and pharmacokinetics. Compared to GSIs studied in the clinic, representative spirocyclic phosphonate 18a(-) features improved selectivity for the inhibition of the PS-1 isoform of γ-secretase (33-fold vs PS-2), which may alleviate the adverse effect profile of the clinical GSIs.

Iminopyrimidinones: a novel pharmacophore for the development of orally active renin inhibitors.

The development of renin inhibitors with favorable oral pharmacokinetic profiles has been a longstanding challenge for the pharmaceutical industry. As part of our work to identify inhibitors of BACE1, we have previously developed iminopyrimidinones as a novel pharmacophore for aspartyl protease inhibition. In this letter we describe how we modified substitution around this pharmacophore to develop a potent, selective and orally active renin inhibitor.

In Vivo Characterization of a Novel γ-Secretase Inhibitor SCH 697466 in Rodents and Investigation of Strategies for Managing Notch-Related Side Effects.

Substantial evidence implicates ß-amyloid (Aß) peptides in the etiology of Alzheimer's disease (AD). Aß is produced by the proteolytic cleavage of the amyloid precursor protein by ß- and γ-secretase suggesting that γ-secretase inhibition may provide therapeutic benefit for AD. Although many γ-secretase inhibitors have been shown to be potent at lowering Aß, some have also been shown to have side effects following repeated administration. All of these side effects can be attributed to altered Notch signaling, another γ-secretase substrate. Here we describe the in vivo characterization of the novel γ-secretase inhibitor SCH 697466 in rodents. Although SCH 697466 was effective at lowering Aß, Notch-related side effects in the intestine and thymus were observed following subchronic administration at doses that provided sustained and complete lowering of Aß. However, additional studies revealed that both partial but sustained lowering of Aßand complete but less sustained lowering of Aß were successful approaches for managing Notch-related side effects. Further, changes in several Notch-related biomarkers paralleled the side effect observations. Taken together, these studies demonstrated that, by carefully varying the extent and duration of Aß lowering by γ-secretase inhibitors, it is possible to obtain robust and sustained lowering of Aß without evidence of Notch-related side effects.

The discovery of fused oxadiazepines as gamma secretase modulators for treatment of Alzheimer's disease.

In an attempt to further improve overall profiles of the oxadiazine series of GSMs, in particular the hERG activity, conformational modifications of the core structure resulted in the identification of fused oxadiazepines such as 7i which had an improved hERG inhibition profile and was a highly efficacious GSM in vitro and in vivo in rats. These SAR explorations offer opportunities to identify potential drugs to treat Alzheimer's disease.

Structure activity relationship studies of tricyclic bispyran sulfone γ-secretase inhibitors.

An investigation is detailed of the structure activity relationships (SAR) of two sulfone side chains of compound (-)-1a (SCH 900229), a potent, PS1-selective γ-secretase inhibitor and clinical candidate for the treatment of Alzheimer's disease. Specifically, 4-CF(3) and 4-Br substituted arylsulfone analogs, (-)-1b and (-)-1c, are equipotent to compound (-)-1a. On the right hand side chain, linker size and terminal substituents of the pendant sulfone group are also investigated.

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 Aß40-42, 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 (Aß40 IC50 = 1.3 nM). Compound (-)-16 demonstrated excellent lowering of Aß 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.

Cyclic hydroxyamidines as amide isosteres: discovery of oxadiazolines and oxadiazines as potent and highly efficacious γ-secretase modulators in vivo.

Cyclic hydroxyamidines were designed and validated as isosteric replacements of the amide functionality. Compounds with these structural motifs were found to be metabolically stable and to possess highly desirable pharmacokinetic profiles. These designs were applied in the identification of γ-secretase modulators leading to highly efficacious agents for reduction of central nervous system Aß(42) in various animal models.

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

Accumulation of the ß-amyloid (Aß) peptides is one of the major pathologic hallmarks in the brains of Alzheimer's disease (AD) patients. Aß is generated by sequential proteolytic cleavage of the amyloid precursor protein (APP) catalyzed by ß- and γ-secretases. Inhibition of Aß 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 Aß production in animals and humans but also cause significant side effects because of the inhibition of Notch processing. The development of GSIs that reduce Aß 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 Aß42 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.

Synthesis and SAR study of tricyclic sulfones as γ-secretase inhibitors: C-6 and C-8 positions.

SAR exploration at C-6 and C-8 positions of the tricyclic sulfone series was carried out. Several functional groups were found to be well tolerated at C-6 and C-8 positions. Selective combination of C-6 and C-8 modification resulted in new tricyclic sulfone analogs with efficacy in in vivo mouse Aß(40) lowering model.

Discovery of fused 5,6-bicyclic heterocycles as γ-secretase modulators.

We herein report the discovery of four series of fused 5,6-bicyclic heterocycles as γ-secretase modulators. Synthesis and SAR of these series are discussed. These compounds represent a new class of γ-secretase modulators that demonstrate moderate to good in vitro potency in inhibiting Aß(42) production.

Design, synthesis, and structure-activity relationship studies of N-arylsulfonyl morpholines as γ-secretase inhibitors.

Design and synthesis of cis-2,6-disubstituted N-arylsulfonyl morpholines as novel γ-secretase inhibitors for the potential treatment of Alzheimer's disease (AD) is reported. Several different small alkyl groups are installed on the left-hand side to lower the CYP3A4 liability while maintaining excellent in vitro potency.

Tetracyclic sulfones as potent gamma-secretase inhibitors: synthesis and structure-activity relationship studies.

Complex tetracyclic sulfones were designed as gamma-secretase inhibitors and a stereoselective synthesis was achieved. Gamma-secretase activity was seen predominately in the (-) enantiomeric series. Compounds such as 2a and 2b showed remarkable in vitro and in vivo potency.

Tricyclic sulfones as orally active gamma-secretase inhibitors: synthesis and structure-activity relationship studies.

Tricyclic sulfones were designed as gamma-secretase inhibitors and found to have excellent potency. Extensive SAR shows that a large number of sulfonamides at position 7 of the tricycle are very well tolerated. Compounds such as 15a and 15c showed remarkable in vivo potency.

Design and synthesis of tricyclic sulfones as gamma-secretase inhibitors with greatly reduced Notch toxicity.

A novel series of tricyclic gamma-secretase inhibitors was designed and synthesized via a conformational analysis of literature compounds. The preliminary results have shown that compounds in this new series have much improved in vitro potency and in vivo profiles. More importantly, they have greatly reduced Notch related toxicity that was associated with previous gamma-secretase inhibitors.

Novel orally active morpholine N-arylsulfonamides gamma-secretase inhibitors with low CYP 3A4 liability.

A new class of 2,6-disubstituted morpholine N-arylsulfonamide gamma-secretase inhibitors was designed based on the introduction of a morpholine core in lieu or piperidine in our lead series. This resulted in compounds with improved CYP 3A4 profiles. Several analogs that were active at lowering Abeta levels in Tg CRND8 mice upon oral administration were identified.