ABSTRACT
Apoptosis Signal-Regulating Kinase-1 (ASK1) is a known member of the Mitogen-Activated Protein Kinase Kinase Kinase (MAP3K) family and upon stimulation will activate the p38- and JNK-pathways leading to cardiac apoptosis, fibrosis, and hypertrophy. Using Structure-Based Drug Design (SBDD) in parallel with deconstruction of a published compound, a novel series of ASK1 inhibitors was optimized, which incorporated a saturated heterocycle proximal to the hinge-binding motif. This yielded a unique chemical series with excellent selectivity across the broader kinome, and desirable drug-like properties. The lead compound (10) is highly soluble and permeable, and exhibits a cellular EC50 = 24 nM and Kd < 1 nM. Of the 350 kinases tested, 10 has an IC50 ≤ 500 nM for only eight of them. This paper will describe the design hypotheses behind this series, key data points during the optimization phase, as well as a possible structural rationale for the kinome selectivity. Based on crystallographic data, the presence of an aliphatic cycle adjacent to the hinge-binder in the active site of the protein kinase showed up in <1% of the >5000 structures in the Protein Data Bank, potentially conferring the selectivity seen in this series.
Subject(s)
MAP Kinase Kinase Kinase 5/antagonists & inhibitors , Protein Kinase Inhibitors/chemistry , Animals , Binding Sites , Catalytic Domain , Crystallography, X-Ray , Drug Design , Humans , Imidazoles/chemistry , Imidazoles/metabolism , Imidazoles/therapeutic use , Inhibitory Concentration 50 , MAP Kinase Kinase Kinase 5/metabolism , Mice , Molecular Dynamics Simulation , Myocardial Reperfusion Injury/drug therapy , Protein Kinase Inhibitors/metabolism , Protein Kinase Inhibitors/therapeutic useABSTRACT
This study examined potential differences in bleeding between apixaban and rivaroxaban, the most commonly utilized direct oral anticoagulants at the Richard L. Roudebush VA Medical Center. Additionally, the analysis included a comparison between observed and literature-reported bleeding rates. This retrospective chart review examined 452 (39%) Veterans receiving rivaroxaban and 716 (61%) Veterans receiving apixaban. Bleeding rates were expressed per 100 patient-years and the overall rates were analyzed as the primary analysis. Secondary objectives included comparisons based on indication and severity, as well as comparisons to literature-reported bleed rates, time to bleeding event, and location of the bleed. The analysis did not detect any statistically significant differences between apixaban and rivaroxaban in terms of overall, (ARR 0.90% per 100 patient-years, 95% CI - 0.58 to 2.38%, p > 0.05) major, (ARR 0.22% per 100 patient-years, 95% CI - 0.74 to 1.17%, p > 0.05) or non-major clinically relevant (ARR 0.35% per 100 patient-years, 95% CI - 0.57 to 1.27%, p > 0.05) bleeding. Observed bleeding for both rivaroxaban and apixaban in the Veteran population exceeded the rates reported by the literature when used for atrial fibrillation (1.96% vs. 0.15%, p < 0.05; 1.08% vs. 0.16%, p < 0.05) but the opposite was seen for long term venous thromboembolism (VTE) treatment (3.97% vs. 8.03%, p < 0.0001; 0.14% vs. 15.51%, p < 0.0001) or extended VTE prophylaxis (0.07% vs 5.98%, p < 0.0001; 0.07% vs 1.88%, p < 0.01). Results from this study suggest these agents impart similar levels of risk, but variations in bleeding risk between the Veteran population and the patients in the original clinical trials may exist.
Subject(s)
Atrial Fibrillation/drug therapy , Blood Coagulation/drug effects , Factor Xa Inhibitors/adverse effects , Hemorrhage/chemically induced , Pyrazoles/adverse effects , Pyridones/adverse effects , Rivaroxaban/adverse effects , Venous Thromboembolism/drug therapy , Administration, Oral , Aged , Aged, 80 and over , Atrial Fibrillation/blood , Atrial Fibrillation/diagnosis , Atrial Fibrillation/epidemiology , Factor Xa Inhibitors/administration & dosage , Female , Hemorrhage/diagnosis , Hemorrhage/epidemiology , Humans , Male , Middle Aged , Pyrazoles/administration & dosage , Pyridones/administration & dosage , Retrospective Studies , Risk Assessment , Risk Factors , Rivaroxaban/administration & dosage , Time Factors , Treatment Outcome , United States/epidemiology , United States Department of Veterans Affairs , Venous Thromboembolism/blood , Venous Thromboembolism/diagnosis , Venous Thromboembolism/epidemiology , Veterans HealthABSTRACT
[This corrects the article DOI: 10.1021/acsmedchemlett.6b00481.].
ABSTRACT
Serine hydrolases are susceptible to potent reversible inhibition by boronic acids. Large collections of chemically diverse boronic acid fragments are commercially available because of their utility in coupling chemistry. We repurposed the approximately 650 boronic acid reagents in our collection as a directed fragment library targeting serine hydrolases and related enzymes. Highly efficient hits (LE > 0.6) often result. The utility of the approach is illustrated with the results against autotaxin, a phospholipase implicated in cardiovascular disease.
Subject(s)
Boronic Acids/chemistry , Phosphoric Diester Hydrolases/metabolism , Serine Proteinase Inhibitors/pharmacology , Small Molecule Libraries/pharmacology , Structure-Activity Relationship , Crystallography, X-Ray , Drug Evaluation, Preclinical/methods , Humans , Nitriles/chemistry , Phosphoric Diester Hydrolases/chemistry , Phosphoric Diester Hydrolases/genetics , Serine Endopeptidases/metabolism , Serine Proteinase Inhibitors/chemistry , Small Molecule Libraries/chemistry , Surface Plasmon ResonanceABSTRACT
Structure-based drug design is an iterative process that is an established means to accelerate lead optimization, and is most powerful when integrated with information from different sources. Herein is described the use of such methods in conjunction with deconstruction and re-optimization of a diverse series of ASK1 chemotypes along with high-throughput screening that lead to the identification of a novel series of efficient ASK1 inhibitors displaying robust MAP3K pathway inhibition.
Subject(s)
Drug Design , MAP Kinase Kinase Kinase 5/antagonists & inhibitors , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/pharmacology , Drug Evaluation, Preclinical , High-Throughput Screening Assays , Humans , MAP Kinase Kinase Kinase 5/chemistry , MAP Kinase Kinase Kinase 5/metabolism , MAP Kinase Signaling System/drug effects , Molecular Docking SimulationABSTRACT
Apoptosis signal-regulating kinase 1 (ASK1/MAP3K) is a mitogen-activated protein kinase family member shown to contribute to acute ischemia/reperfusion injury. Using structure-based drug design, deconstruction, and reoptimization of a known ASK1 inhibitor, a lead compound was identified. This compound displayed robust MAP3K pathway inhibition and reduction of infarct size in an isolated perfused heart model of cardiac injury.
ABSTRACT
Catechol O-methyl transferase belongs to the diverse family of S-adenosyl-l-methionine transferases. It is a target involved in the treatment of Parkinson's disease. Here we present a fragment-based screening approach to discover noncatechol derived COMT inhibitors which bind at the SAM binding pocket. We describe the identification and characterization of a series of highly ligand efficient SAM competitive bisaryl fragments (LE = 0.33-0.58). We also present the first SAM-competitive small-molecule COMT co-complex crystal structure.
Subject(s)
Catechol O-Methyltransferase Inhibitors , S-Adenosylmethionine/metabolism , Animals , Binding Sites , Catechol O-Methyltransferase/chemistry , Humans , Kinetics , Mice , Models, Molecular , Protein Conformation , Pyrazoles/chemistry , Rats , S-Adenosylmethionine/chemistry , Structure-Activity Relationship , Thiazoles/chemistry , Triazoles/chemistryABSTRACT
We report here the synthesis and SAR of a new series of thieno[3,2-d]pyrimidines as potent Tpl2 kinase inhibitors. The proposed binding mode suggests the potential flipped binding mode depending on the substitution. Biacore studies show evidence of binding of these molecules to the protein kinase. The kinome inhibition profile of these molecules suggests good selectivity.
Subject(s)
MAP Kinase Kinase Kinases/antagonists & inhibitors , Protein Kinase Inhibitors/chemical synthesis , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins/antagonists & inhibitors , Animals , Drug Discovery , Drug Evaluation, Preclinical , Humans , Inhibitory Concentration 50 , MAP Kinase Kinase Kinases/metabolism , Microsomes, Liver , Molecular Targeted Therapy , Monocytes , Neoplasms/drug therapy , Phosphorylation , Protein Binding , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/metabolism , Proto-Oncogene Proteins/metabolism , Pyrimidines/chemistry , Rats , Structure-Activity Relationship , Substrate SpecificityABSTRACT
Synthesis, modeling and structure-activity relationship of indazoles as inhibitors of Tpl2 kinase are described. From a high throughput screening effort, we identified an indazole hit compound 5 that has a single digit micromolar Tpl2 activity. Through SAR modifications at the C3 and C5 positions of the indazole, we discovered compound 31 with good potency in LANCE assay and cell-based p-Erk assay.
Subject(s)
Drug Discovery , Enzyme Inhibitors/pharmacology , Indazoles/pharmacology , MAP Kinase Kinase Kinases/antagonists & inhibitors , Proto-Oncogene Proteins/antagonists & inhibitors , Dose-Response Relationship, Drug , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/chemistry , Humans , Indazoles/chemical synthesis , Indazoles/chemistry , MAP Kinase Kinase Kinases/metabolism , Models, Molecular , Molecular Structure , Monocytes/enzymology , Monocytes/metabolism , Proto-Oncogene Proteins/metabolism , Stereoisomerism , Structure-Activity RelationshipABSTRACT
Acidic mammalian chitinase (AMCase) is a member of the glycosyl hydrolase 18 family (EC 3.2.1.14) that has been implicated in the pathophysiology of allergic airway disease such as asthma. Small molecule inhibitors of AMCase were identified using a combination of high-throughput screening, fragment screening, and virtual screening techniques and characterized by enzyme inhibition and NMR and Biacore binding experiments. X-ray structures of the inhibitors in complex with AMCase revealed that the larger more potent HTS hits, e.g. 5-(4-(2-(4-bromophenoxy)ethyl)piperazine-1-yl)-1H-1,2,4-triazol-3-amine 1, spanned from the active site pocket to a hydrophobic pocket. Smaller fragments identified by FBS occupy both these pockets independently and suggest potential strategies for linking fragments. Compound 1 is a 200 nM AMCase inhibitor which reduced AMCase enzymatic activity in the bronchoalveolar lavage fluid in allergen-challenged mice after oral dosing.
Subject(s)
Chitinases/antagonists & inhibitors , Models, Molecular , Piperazines/chemical synthesis , Triazoles/chemical synthesis , Allergens/immunology , Animals , Bronchoalveolar Lavage Fluid , Catalytic Domain , Crystallography, X-Ray , Female , Hydrophobic and Hydrophilic Interactions , Magnetic Resonance Spectroscopy , Mice , Mice, Inbred C57BL , Piperazines/chemistry , Piperazines/pharmacology , Protein Binding , Respiratory Hypersensitivity/drug therapy , Respiratory Hypersensitivity/enzymology , Respiratory Hypersensitivity/immunology , Structure-Activity Relationship , Surface Plasmon Resonance , Triazoles/chemistry , Triazoles/pharmacologyABSTRACT
Using a focused screen of biogenic amine compounds we identified a novel series of H(3)R antagonists. A preliminary SAR study led to reduction of MW while increasing binding affinity and potency. Optimization of the physical properties of the series led to (S)-6n, with improved brain to plasma exposure and efficacy in both water intake and novel object recognition models.
Subject(s)
Benzamides/chemistry , Benzimidazoles/chemistry , Histamine H3 Antagonists/chemistry , Pyrrolidines/chemistry , Receptors, Histamine H3 , Animals , Benzamides/blood , Benzamides/metabolism , Benzimidazoles/blood , Benzimidazoles/metabolism , Caco-2 Cells , Cell Line , Histamine H3 Antagonists/blood , Histamine H3 Antagonists/metabolism , Humans , Indoles/blood , Indoles/chemistry , Indoles/metabolism , Protein Binding , Pyrrolidines/blood , Pyrrolidines/metabolism , Rats , Receptors, Histamine H3/blood , Receptors, Histamine H3/metabolismABSTRACT
8,8-Diphenyl-2,3,4,8-tetrahydroimidazo[1,5-a]pyrimidin-6-amine (1) was identified through HTS, as a weak (micromolar) inhibitor of BACE1. X-Ray crystallographic studies indicate the 2-aminoimidazole ring forms key H-bonding interactions with Asp32 and Asp228 in the catalytic site of BACE1. Lead optimization using structure-based focused libraries led to the identification of low nanomolar BACE1 inhibitors such as 20b with substituents which extend from the S(1) to the S(3) pocket.
Subject(s)
Amyloid Precursor Protein Secretases/antagonists & inhibitors , Enzyme Inhibitors/chemistry , Hydantoins/chemistry , Imidazoles/chemistry , Amyloid Precursor Protein Secretases/metabolism , Binding Sites , Catalytic Domain , Crystallography, X-Ray , Drug Discovery , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/pharmacology , Humans , Hydantoins/chemical synthesis , Hydantoins/pharmacology , Hydrogen Bonding , Imidazoles/chemical synthesis , Imidazoles/pharmacologyABSTRACT
C5a is a terminal product of the complement cascade that activates and attracts inflammatory cells including granulocytes, mast cells and macrophages via a specific GPCR, the C5a receptor (C5aR). Inhibition of C5a/C5aR interaction has been shown to be efficacious in several animal models of autoimmune diseases, including RA, SLE and asthma. This account reports the discovery of a new class of C5aR antagonists through high-throughput screening. The lead compounds in this series are selective and block C5a binding, C5a-promoted calcium flux in human neutrophils with nanomolar potency.
Subject(s)
Receptor, Anaphylatoxin C5a/antagonists & inhibitors , Sulfonamides/chemistry , Animals , Cell Line , High-Throughput Screening Assays , Humans , Mice , Molecular Conformation , Neutrophils/immunology , Neutrophils/metabolism , Protein Binding , Receptor, Anaphylatoxin C5a/metabolism , Sulfonamides/chemical synthesis , Sulfonamides/pharmacologyABSTRACT
Vanin-1 is a pantetheinase that catalyzes the hydrolysis of pantetheine to produce pantothenic acid (vitamin B5) and cysteamine. Reported here is a highly sensitive fluorescent assay using a novel fluorescently labeled pantothenate derivative. The assay has been used for characterization of a soluble version of human vanin-1 recombinant protein, identification and characterization of hits from high-throughput screening (HTS), and quantification of vanin pantothenase activity in cell lines and tissues. Under optimized assay conditions, we quantified vanin pantothenase activity in tissue lysate and found low activity in lung and liver but high activity in kidney. We demonstrated that the purified recombinant vanin-1 consisting of the extracellular portion without the glycosylphosphatidylinositol (GPI) linker was highly active with an apparent K(m) of 28 microM for pantothenate-7-amino-4-methylcoumarin (pantothenate-AMC), which was converted to pantothenic acid and AMC based on liquid chromatography-mass spectrometry (LC-MS) analysis. The assay also performed well in a 384-well microplate format under initial rate conditions (10% conversion) with a signal-to-background ratio (S/B) of 7 and a Z factor of 0.75. Preliminary screening of a library of 1280 pharmaceutically active compounds identified inhibitors with novel chemical scaffolds. This assay will be a powerful tool for target validation and drug lead identification and characterization.
Subject(s)
Amidohydrolases/metabolism , Chromatography, High Pressure Liquid/methods , Enzyme Inhibitors/chemistry , Mass Spectrometry/methods , Amidohydrolases/antagonists & inhibitors , Amidohydrolases/genetics , Amino Acid Sequence , Animals , Cell Line , Enzyme Inhibitors/pharmacology , Fluorescent Dyes/chemistry , GPI-Linked Proteins , High-Throughput Screening Assays , Humans , Kidney/enzymology , Mice , Molecular Sequence Data , Pantothenic Acid/chemistry , Recombinant Proteins/antagonists & inhibitors , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Spectrophotometry, UltravioletABSTRACT
The mammalian target of rapamycin (mTOR) is a central regulator of cell growth, metabolism, and angiogenesis and an emerging target in cancer research. High throughput screening (HTS) of our compound collection led to the identification of 3-(4-morpholin-4-yl-1-piperidin-4-yl-1H-pyrazolo[3,4-d]pyrimidin-6-yl)phenol (5a), a modestly potent and nonselective inhibitor of mTOR and phosphoinositide 3-kinase (PI3K). Optimization of compound 5a, employing an mTOR homology model based on an X-ray crystal structure of closely related PI3Kgamma led to the discovery of 6-(1H-indol-5-yl)-4-morpholin-4-yl-1-[1-(pyridin-3-ylmethyl)piperidin-4-yl]-1H-pyrazolo[3,4-d]pyrimidine (5u), a potent and selective mTOR inhibitor (mTOR IC(50) = 9 nM; PI3Kalpha IC(50) = 1962 nM). Compound 5u selectively inhibited cellular biomarker of mTORC1 (P-S6K, P-4EBP1) and mTORC2 (P-AKT S473) over the biomarker of PI3K/PDK1 (P-AKT T308) and did not inhibit PI3K-related kinases (PIKKs) in cellular assays. These pyrazolopyrimidines represent an exciting new series of mTOR-selective inhibitors with potential for development for cancer therapy.
Subject(s)
Drug Discovery , Protein Kinase Inhibitors/pharmacology , Protein Kinases/metabolism , Pyrimidines/pharmacology , Binding, Competitive , Cell Line, Tumor , Humans , Inhibitory Concentration 50 , Models, Molecular , Molecular Conformation , Molecular Weight , Protein Kinase Inhibitors/chemical synthesis , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/metabolism , Protein Kinases/chemistry , Pyrimidines/chemical synthesis , Pyrimidines/chemistry , Pyrimidines/metabolism , Signal Transduction/drug effects , Substrate Specificity , TOR Serine-Threonine KinasesABSTRACT
The mammalian target of rapamycin (mTOR) is centrally involved in cell growth, metabolism, and angiogenesis. While showing clinical efficacy in a subset of tumors, rapamycin and rapalogs are specific and allosteric inhibitors of mTOR complex 1 (mTORC1), but they do not directly inhibit mTOR complex 2 (mTORC2), an emerging player in cancer. Here, we report chemical structure and biological characterization of three pyrazolopyrimidine ATP-competitive mTOR inhibitors, WAY-600, WYE-687, and WYE-354 (IC(50), 5-9 nmol/L), with significant selectivity over phosphatidylinositol 3-kinase (PI3K) isofoms (>100-fold). Unlike the rapalogs, these inhibitors acutely blocked substrate phosphorylation by mTORC1 and mTORC2 in vitro and in cells in response to growth factor, amino acids, and hyperactive PI3K/AKT. Unlike the inhibitors of PI3K or dual-pan PI3K/mTOR, cellular inhibition of P-S6K1(T389) and P-AKT(S473) by the pyrazolopyrimidines occurred at significantly lower inhibitor concentrations than those of P-AKT(T308) (PI3K-PDK1 readout), showing mTOR selectivity in cellular setting. mTOR kinase inhibitors reduced AKT downstream function and inhibited proliferation of diverse cancer cell lines. These effects correlated with a strong G(1) cell cycle arrest in both the rapamycin-sensitive and rapamycin-resistant cells, selective induction of apoptosis, repression of global protein synthesis, and down-regulation of angiogenic factors. When injected into tumor-bearing mice, WYE-354 inhibited mTORC1 and mTORC2 and displayed robust antitumor activity in PTEN-null tumors. Together, our results highlight mechanistic differentiation between rapalogs and mTOR kinase inhibitors in targeting cancer cell growth and survival and provide support for clinical development of mTOR kinase inhibitors as new cancer therapy.
Subject(s)
Adenosine Triphosphate/metabolism , Protein Kinase Inhibitors/pharmacology , Purines/pharmacology , Pyrazoles/pharmacology , Pyrimidines/pharmacology , Transcription Factors/antagonists & inhibitors , Angiogenic Proteins/antagonists & inhibitors , Animals , Apoptosis/drug effects , Binding, Competitive , Cell Line, Tumor/metabolism , Down-Regulation , G1 Phase/drug effects , HCT116 Cells , HT29 Cells , Humans , Mechanistic Target of Rapamycin Complex 1 , Multiprotein Complexes , Protein Kinase Inhibitors/metabolism , Protein Kinases , Proteins , Purines/metabolism , Pyrazoles/metabolism , Pyrimidines/metabolism , Rats , Sirolimus/pharmacology , TOR Serine-Threonine Kinases , Transcription Factors/metabolismABSTRACT
A series of 1-aminoethyl-3-arylsulfonyl-1H-pyrrolo[2,3-b]pyridines 10a-z was prepared as novel 5-HT(6) ligands. The best compounds were high affinity, full agonists at 5-HT(6) receptors. Several agonists demonstrated good selectivity over other serotonergic and dopaminergic receptors. Acute administration of selective agonist 10e significantly increased extracellular GABA concentrations in rat frontal cortex. This compound also reduced adjunctive drinking behavior in the rat schedule-induced polydipsia assay, possibly predictive of efficacy in obsessive compulsive disorder and other anxiety related disorders.
Subject(s)
Cerebral Cortex/drug effects , Drinking Behavior/drug effects , Receptors, Serotonin/metabolism , Serotonin Receptor Agonists/chemistry , Serotonin Receptor Agonists/pharmacology , Animals , Cerebral Cortex/metabolism , Glutamic Acid/analysis , Glutamic Acid/metabolism , HeLa Cells , Humans , Protein Binding , Rats , Serotonin Receptor Agonists/administration & dosage , Serotonin Receptor Agonists/chemical synthesis , gamma-Aminobutyric Acid/analysis , gamma-Aminobutyric Acid/metabolismABSTRACT
A series of 4-indolylamino-5-phenyl-3-pyridinecarbonitrile inhibitors of PKCtheta were synthesized as potential anti-inflammatory agents. The effects of specific substitution on the 5-phenyl moiety and variations of the positional isomers of the 4-indolylamino substituent were explored. This study led to the discovery of compound 12d, which had an IC(50) value of 18nM for the inhibition of PKCtheta.
Subject(s)
Isoenzymes/antagonists & inhibitors , Protein Kinase C/antagonists & inhibitors , Protein Kinase Inhibitors/chemical synthesis , Pyridines/chemical synthesis , Adenosine Triphosphate/chemistry , Animals , Anti-Inflammatory Agents/pharmacology , Chemistry, Pharmaceutical/methods , Drug Design , Humans , Inhibitory Concentration 50 , Isoenzymes/chemistry , Mice , Models, Chemical , Molecular Structure , Protein Isoforms , Protein Kinase C/chemistry , Protein Kinase C-theta , Protein Kinase Inhibitors/pharmacology , Pyridines/pharmacology , Structure-Activity RelationshipABSTRACT
Accumulation of beta-amyloid (Abeta), produced by the proteolytic cleavage of amyloid precursor protein (APP) by beta- and gamma-secretase, is widely believed to be associated with Alzheimer's disease (AD). Research around the high-throughput screening hit (S)-4-chlorophenylsulfonyl isoleucinol led to the identification of the Notch-1-sparing (9.5-fold) gamma-secretase inhibitor (S)-N-(5-chlorothiophene-2-sulfonyl)-beta,beta-diethylalaninol 7.b.2 (Abeta(40/42) EC(50)=28 nM), which is efficacious in reduction of Abeta production in vivo.
Subject(s)
Alzheimer Disease/drug therapy , Amyloid Precursor Protein Secretases/antagonists & inhibitors , Isoleucine/analogs & derivatives , Receptor, Notch1/metabolism , Alcohols , Amyloid Precursor Protein Secretases/metabolism , Amyloid beta-Protein Precursor/chemistry , Animals , Drug Design , Humans , Isoleucine/chemistry , Models, Chemical , Propanolamines/chemistry , Sulfonamides/chemistryABSTRACT
SAR on HTS hits 1 and 2 led to the potent, Notch-1-sparing GSI 9, which lowered brain Abeta in Tg2576 mice at 100 mg/kg po. Converting the metabolically labile methyl groups in 9 to trifluoromethyl groups afforded the more stable analogue 10, which had improved in vivo potency. Further side chain modification afforded the potent Notch-1-sparing GSI begacestat (5), which was selected for development for the treatment of Alzheimer's disease.