On the basis of our observation that the biaryl substituent of iminopyrimidinone 7 must be in a pseudoaxial conformation to occupy the contiguous S1–S3 subsites of BACE1, we have designed a novel ...fused bicyclic iminopyrimidinone scaffold intended to favor this bioactive conformation. Strategic incorporation of a nitrogen atom in the new constrained ring allowed us to develop SAR around the S2′ binding pocket and ultimately resulted in analogues with low nanomolar potency for BACE1. In particular, optimization of the prime side substituent led to major improvements in potency by displacement of two conserved water molecules from a region near S2′. Further optimization of the pharmacokinetic properties of this fused pyrrolidine series, in conjunction with facile access to a rat pharmacodynamic model, led to identification of compound 43, which is an orally active, brain penetrant inhibitor that reduces Aβ40 in the plasma, CSF, and cortex of rats in a dose-dependent manner.
Packed-column supercritical fluid chromatography (pSFC) coupled to an atmospheric pressure chemical ionization (APCI) source and a tandem mass spectrometer (MS/MS) for rapid and simultaneous ...determination of clozapine, ondansetron, tolbutamide and primidone in in vitro samples was developed in support of metabolic stability experiments. The effects of the eluent flow-rate and composition as well as the nebulizer temperatures on the ionization efficiency of the analytes in positive ion mode under normal phase pSFC conditions were studied. The metabolic stability of the test drug components through microsomal incubation by the proposed pSFC–APCI/MS/MS approaches requiring approximately 1
min per samples were evaluated with respect to specificity, durability and accuracy. These metabolic stability results obtained by pSFC–MS/MS methods are in a good agreement with those obtained by fast high-performance liquid chromatography/tandem mass spectrometry (HPLC–MS/MS) method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Cytochrome P450 inhibition studies are performed in the pharmaceutical industry in the discovery stage to screen candidates that may have the potential for clinical drug-drug interactions. A 96-well ...microtiter plate assay using recombinant cytochrome P450 (Supersomes) has been used to increase the overall throughput. The IC(50) values for the inhibition of CYP3A4 by 52 new chemical entities (NCEs) were determined using the Supersomes assay with resorufin benzyl ether as a substrate, and the data were compared with those obtained in human liver microsomes (HLM) using midazolam as a substrate. Among the 52 compounds tested, 25 showed IC(50) values within a 5-fold difference in the two assays. For all compounds that showed a >5-fold difference, the IC(50) values in the Supersomes assay were lower than those obtained in HLM, except for one compound. Further studies suggested that this discrepancy was not related to difference in protein concentrations between the two assays. In addition, the IC(50) values for 16 compounds with a wide range of inhibition potency were determined in HLM using testosterone and dextromethorphan as substrates. The results showed an 80 to 93% match within a 5-fold difference between the three probe substrates. However, for certain compounds including ketoconazole, there were substrate-dependent differences in the inhibition. The results suggest that the difference between the Supersomes and HLM could be partially attributed to differences in the substrate used, and to metabolism by other cytochrome P450s present in the HLM but not in the Supersomes. Furthermore, multiple CYP3A4 substrates should be used to improve the reliability of estimating potential drug-drug interaction of NCEs.
From an initial lead 1, a structure-based design approach led to identification of a novel, high-affinity iminohydantoin BACE1 inhibitor that lowers CNS-derived Aβ following oral administration to ...rats. Herein we report SAR development in the S3 and F′ subsites of BACE1 for this series, the synthetic approaches employed in this effort, and in vivo data for the optimized compound.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A number of novel amidine containing heterocycles were designed to reproduce the unique interaction pattern, revealed by X-ray crystallography, between the BACE-1 catalytic diad and a weak NMR ...screening hit (3), with special attention paid to maintaining the appropriate basicity and limiting the number of H-bonding donors of these scaffolds. The iminohydantoin cores (10 and 23) were examined first and found to interact with the catalytic diad in one of two binding modes (A and B), each with the iminohydantoin core flipped 180° in relation to the other. The amidine structural motif within each core forms a bidentate interaction with a different aspartic acid of the catalytic diad. Both modes reproduced a highly conserved interaction pattern between the inhibitors and the catalytic aspartates, as revealed by 3. Potent iminohydantoin BACE-1 inhibitors have been obtained, validating the molecular design as aspartyl protease catalytic site inhibitors. Brain penetrant small molecule BACE inhibitors with high ligand efficiencies have been discovered, enabling multiple strategies for further development of these inhibitors into highly potent, selective and in vivo efficacious BACE inhibitors.
We describe successful efforts to optimize the in vivo profile and address off-target liabilities of a series of BACE1 inhibitors represented by 6 that embodies the recently validated fused ...pyrrolidine iminopyrimidinone scaffold. Employing structure-based design, truncation of the cyanophenyl group of 6 that binds in the S3 pocket of BACE1 followed by modification of the thienyl group in S1 was pursued. Optimization of the pyrimidine substituent that binds in the S2′–S2″ pocket of BACE1 remediated time-dependent CYP3A4 inhibition of earlier analogues in this series and imparted high BACE1 affinity. These efforts resulted in the discovery of difluorophenyl analogue 9 (MBi-4), which robustly lowered CSF and cortex Aβ40 in both rats and cynomolgus monkeys following a single oral dose. Compound 9 represents a unique molecular shape among BACE inhibitors reported to potently lower central Aβ in nonrodent preclinical species.
Herein we describe structure–activity relationship (SAR) and metabolite identification (Met-ID) studies that provided insight into the origin of time-dependent inhibition (TDI) of cytochrome P450 3A4 ...(CYP3A4) by compound 1. Collectively, these efforts revealed that bioactivation of the fluoropyrimidine moiety of 1 led to reactive metabolite formation via oxidative defluorination and was responsible for the observed TDI. We discovered that substitution at both the 4- and 6-positions of the 5-fluoropyrimidine of 1 was necessary to ameliorate this TDI as exemplified by compound 19.
Inhibition of BACE1 to prevent brain Aβ peptide formation is a potential disease-modifying approach to the treatment of Alzheimer’s disease. Despite over a decade of drug discovery efforts, the ...identification of brain-penetrant BACE1 inhibitors that substantially lower CNS Aβ levels following systemic administration remains challenging. In this report we describe structure-based optimization of a series of brain-penetrant BACE1 inhibitors derived from an iminopyrimidinone scaffold. Application of structure-based design in tandem with control of physicochemical properties culminated in the discovery of compound 16, which potently reduced cortex and CSF Aβ40 levels when administered orally to rats.
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IJS, KILJ, NUK, PNG, UL, UM, UPUK
Cytochrome P450 (CYP) inhibition studies are often performed on new chemical entities during the drug discovery stage. However, advances in combinatorial chemistry mean that an unprecedented number ...of compounds now require such evaluation. Recently, a microtiter plate assay that utilizes individually expressed CYP enzymes (Supersomes™) has been developed to facilitate this process. The authors discuss some of their experiences with this technology and its potential impact for higher throughput CYP2D6 enzyme inhibition studies.
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IJS, IMTLJ, KILJ, KISLJ, NUK, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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