Spiropiperidine Sultam and Lactam Templates: Diastereoselective Overman Rearrangement and Metathesis followed by NH Arylation.

We report the diastereoselective synthesis of novel spiropiperidine templates for use in SAR studies of ß-secretase (BACE) inhibitors and also as versatile ligands for other receptor types. The overall synthetic approach stems from chiral starting material benzyl (S)-2-methyl-4-oxopiperidine-1-carboxylate and employs an Overman rearrangement to control the stereochemistry at the quaternary center. This process is followed by a Grubbs metathesis to close a five-membered "top" ring to form an α,ß-unsaturated lactam or an α,ß-unsaturated sultam. We also demonstrate that this chemistry can accommodate additional substituents on the lactam/sultam ring and allows late stage sequential functionalization of the amine and amide nitrogens to rapidly produce diverse analogues.

Utilizing on- and off-line monitoring tools to follow a kinetic resolution step during flow synthesis.

In situ reaction monitoring tools offer the ability to track the progress of a synthetic reaction in real time to facilitate reaction optimization and provide kinetic/mechanistic insight. Herein, we report the utilization of flow NMR, flow IR, and other off-line spectroscopy tools to monitor the progress of a flow chemistry reaction. The on-line and off-line tools were selected to facilitate the stereoselective kinetic resolution of a key racemic monomer, which lacked a chromophore, making conventional reaction monitoring difficult. Copyright © 2016 John Wiley & Sons, Ltd.

Visible-Light-Initiated Manganese Catalysis for C-H Alkylation of Heteroarenes: Applications and Mechanistic Studies.

A visible-light-driven Minisci protocol that employs an inexpensive earth-abundant metal catalyst, decacarbonyldimanganese Mn2 (CO)10 , to generate alkyl radicals from alkyl iodides has been developed. This Minisci protocol is compatible with a wide array of sensitive functional groups, including oxetanes, sugar moieties, azetidines, tert-butyl carbamates (Boc-group), cyclobutanes, and spirocycles. The robustness of this protocol is demonstrated on the late-stage functionalization of complex nitrogen-containing drugs. Photophysical and DFT studies indicate a light-initiated chain reaction mechanism propagated by . Mn(CO)5 . The rate-limiting step is the iodine abstraction from an alkyl iodide by . Mn(CO)5 .

Iron-mediated modular decarboxylative cross-nucleophile coupling.

Carboxylic acids are valuable building blocks for pharmaceutical discovery because of their chemical stability, commercial availability, and structural diversity. Decarboxylative coupling reactions enable versatile functionalization of these feedstock chemicals, but many of the most general methods require prefunctionalization of carboxylic acids with redox-active moieties. These internal oxidants can be costly, their installation impedes rapid library synthesis, and their use results in environmentally problematic organic byproducts. We report herein a method for the direct decarboxylative cross-coupling of native carboxylic acids with nucleophilic coupling partners mediated by inexpensive, terrestrially abundant, and nontoxic Fe(III) salts. This method involves an initial photochemical decarboxylation followed by radical-polar crossover, which enables the construction of diverse carbon-carbon, carbon-oxygen, and carbon-nitrogen bonds with remarkable generality.

Decarboxylative cross-nucleophile coupling via ligand-to-metal charge transfer photoexcitation of Cu(II) carboxylates.

Reactions that enable carbon-nitrogen, carbon-oxygen and carbon-carbon bond formation lie at the heart of synthetic chemistry. However, substrate prefunctionalization is often needed to effect such transformations without forcing reaction conditions. The development of direct coupling methods for abundant feedstock chemicals is therefore highly desirable for the rapid construction of complex molecular scaffolds. Here we report a copper-mediated, net-oxidative decarboxylative coupling of carboxylic acids with diverse nucleophiles under visible-light irradiation. Preliminary mechanistic studies suggest that the relevant chromophore in this reaction is a Cu(II) carboxylate species assembled in situ. We propose that visible-light excitation to a ligand-to-metal charge transfer (LMCT) state results in a radical decarboxylation process that initiates the oxidative cross-coupling. The reaction is applicable to a wide variety of coupling partners, including complex drug molecules, suggesting that this strategy for cross-nucleophile coupling would facilitate rapid compound library synthesis for the discovery of new pharmaceutical agents.

Utilizing structures of CYP2D6 and BACE1 complexes to reduce risk of drug-drug interactions with a novel series of centrally efficacious BACE1 inhibitors.

In recent years, the first generation of ß-secretase (BACE1) inhibitors advanced into clinical development for the treatment of Alzheimer's disease (AD). However, the alignment of drug-like properties and selectivity remains a major challenge. Herein, we describe the discovery of a novel class of potent, low clearance, CNS penetrant BACE1 inhibitors represented by thioamidine 5. Further profiling suggested that a high fraction of the metabolism (>95%) was due to CYP2D6, increasing the potential risk for victim-based drug-drug interactions (DDI) and variable exposure in the clinic due to the polymorphic nature of this enzyme. To guide future design, we solved crystal structures of CYP2D6 complexes with substrate 5 and its corresponding metabolic product pyrazole 6, which provided insight into the binding mode and movements between substrate/inhibitor complexes. Guided by the BACE1 and CYP2D6 crystal structures, we designed and synthesized analogues with reduced risk for DDI, central efficacy, and improved hERG therapeutic margins.

Measurement of atropisomer racemization kinetics using segmented flow technology.

When stable atropisomers are encountered by drug discovery teams, they can have important implications due to potential differences in their biological activity, pharmacokinetics, and toxicity. Knowledge of an atropisomer's activation parameters for interconversion is required to facilitate informed decisions on how to proceed. Herein, we communicate the development of a new method for the rapid measurement of atropisomer racemization kinetics utilizing segmented flow technology. This method leverages the speed, accuracy, low sample requirement, safety, and semiautomated nature of flow instrumentation to facilitate the acquisition of kinetics data required for experimentally probing atropisomer activation parameters. Measured kinetics data obtained for the atropo isomerization of AMPA antagonist CP-465021 using segmented flow and traditional thermal methods were compared to validate the method.

Application of structure-based drug design and parallel chemistry to identify selective, brain penetrant, in vivo active phosphodiesterase 9A inhibitors.

Phosphodiesterase 9A inhibitors have shown activity in preclinical models of cognition with potential application as novel therapies for treating Alzheimer's disease. Our clinical candidate, PF-04447943 (2), demonstrated acceptable CNS permeability in rats with modest asymmetry between central and peripheral compartments (free brain/free plasma = 0.32; CSF/free plasma = 0.19) yet had physicochemical properties outside the range associated with traditional CNS drugs. To address the potential risk of restricted CNS penetration with 2 in human clinical trials, we sought to identify a preclinical candidate with no asymmetry in rat brain penetration and that could advance into development. Merging the medicinal chemistry strategies of structure-based design with parallel chemistry, a novel series of PDE9A inhibitors was identified that showed improved selectivity over PDE1C. Optimization afforded preclinical candidate 19 that demonstrated free brain/free plasma ≥ 1 in rat and reduced microsomal clearance along with the ability to increase cyclic guanosine monophosphosphate levels in rat CSF.