Development of a Divergent Synthesis of Pleurotinoid Natural Products.

Herein, we describe the evolution of our syntheses of the pleurotinoid natural products pleurotin (1), pleurogrisein (3), and 4-hydroxypleurogrisein (4). An approach based on a proximity-induced intramolecular Diels-Alder cycloaddition of a transient ortho-quinone dimethide (e.g., 6, Scheme 1) was inferior to an alternative construction featuring Gao's titanium(IV)-mediated photoenolization Diels-Alder coupling of ortho-tolualdehyde 20 with functionalized hydrindenone 22. While this pairing exhibited the desired stereoface selectivity and produced cis-fused hydrindanone 23, the successful realization of our syntheses of 1, 3, and 4 required a post-Diels-Alder epimerization of the unactivated stereocenter at C-5 in compound 23. Ultimately, it was possible to generate a reactive oxygen-centered radical via a reductive homolytic cleavage of the N-O bond in 23 and capitalize on its ability to break the C5-H bond in an intramolecular 1,5-hydrogen atom transfer (HAT). The carbon radical arising from this pivotal 1,5-HAT was subsequently trapped in situ by an exogenous thiol in a kinetically controlled HAT reaction to establish the natural configuration at C-5. The successful flipping of the cis-hydrindane in 23 to the challenging trans configuration in 24 provided a firm foundation for a formal synthesis of pleurotin (1), as well as syntheses of pleurogrisein (3) and 4-hydroxypleurogrisein (4).

Optimization of Metabolic and Renal Clearance in a Series of Indole Acid Direct Activators of 5'-Adenosine Monophosphate-Activated Protein Kinase (AMPK).

Optimization of the pharmacokinetic (PK) properties of a series of activators of adenosine monophosphate-activated protein kinase (AMPK) is described. Derivatives of the previously described 5-aryl-indole-3-carboxylic acid clinical candidate (1) were examined with the goal of reducing glucuronidation rate and minimizing renal excretion. Compounds 10 (PF-06679142) and 14 (PF-06685249) exhibited robust activation of AMPK in rat kidneys as well as desirable oral absorption, low plasma clearance, and negligible renal clearance in preclinical species. A correlation of in vivo renal clearance in rats with in vitro uptake by human and rat renal organic anion transporters (human OAT/rat Oat) was identified. Variation of polar functional groups was critical to mitigate active renal clearance mediated by the Oat3 transporter. Modification of either the 6-chloroindole core to a 4,6-difluoroindole or the 5-phenyl substituent to a substituted 5-(3-pyridyl) group provided improved metabolic stability while minimizing propensity for active transport by OAT3.

An evolved oxazolidinone with selective potency against Mycobacterium tuberculosis and gram positive bacteria.

Innovation of new antibacterials that are effective against strains that have developed resistance to existing drugs would strengthen our ability to treat and subsequently control spread of pathogenic bacteria. Increasing incidence of infections with drug resistant bacteria has become a common occurrence in recent times. We have developed an evolved oxazolidinone, T145, which inhibits growth of Enterococcus faecalis, Staphylococcus aureus and Mycobacterium tuberculosis (Mtb) with sub µg/ml potencies that are potentially therapeutically valuable. The oxazolidinone is bactericidal against Mtb but bacteriostatic against E. faecalis and S. aureus. In addition to therapeutically valuable potency and bactericidal activity against Mtb, T145 minimizes selection of spontaneous resistant mutants, a trait that prolongs longevity of a drug in clinical use.

Strategies for skeletal muscle targeting in drug discovery.

The targeting of drugs to skeletal muscle is an emerging area of research. Driven by the need for new therapies to treat a range of muscle-associated diseases, these strategies aim to provide improved drug exposure at the site of action in skeletal muscle with reduced concentration in other tissues where unwanted side effects could occur. By interacting with muscle-specific cell surface recognition elements, both tissue localization and selective uptake into skeletal muscle cells can be achieved. The design of molecules that are substrates for muscle uptake transporters can provide concentration in m uscle tissue. For example, drug conjugates with carnitine can provide improved muscle uptake via OCTN2 transport. Binding to muscle surface recognition elements followed by endocytosis can allow even large molecules such as antibodies to enter muscle cells. Monoclonal antibody 3E10 demonstrated selective uptake into skeletal muscle in vivo. Hybrid adeno-associated viral vectors have recently shown promise for high skeletal muscle selectivity in gene transfer applications. Delivery technology methods, including electroporation of DNA plasmids, have also been investigated for selective muscle uptake. This review discusses challenges and opportunities for skeletal muscle targeting, highlighting specific examples and areas in need of additional research.

Identification of a novel conformationally constrained glucagon receptor antagonist.

Identification of orally active, small molecule antagonists of the glucagon receptor represents a novel treatment paradigm for the management of type 2 diabetes mellitus. The present work discloses novel glucagon receptor antagonists, identified via conformational constraint of current existing literature antagonists. Optimization of lipophilic ligand efficiency (LLE or LipE) culminated in enantiomers (+)-trans-26 and (-)-trans-27 which exhibit good physicochemical and in vitro drug metabolism profiles. In vivo, significant pharmacokinetic differences were noted with the two enantiomers, which were primarily driven through differences in clearance rates. Enantioselective oxidation by cytochrome P450 was ruled out as a causative factor for pharmacokinetic differences.

Chemical Probe Identification Platform for Orphan GPCRs Using Focused Compound Screening: GPR39 as a Case Example.

Orphan G protein-coupled receptors (oGPCRs) are a class of integral membrane proteins for which endogenous ligands or transmitters have not yet been discovered. Transgenic animal technologies have uncovered potential roles for many of these oGPCRs, providing new targets for the treatment of various diseases. Understanding signaling pathways of oGPCRs and validating these receptors as potential drug targets requires the identification of chemical probe compounds to be used in place of endogenous ligands to interrogate these receptors. A novel chemical probe identification platform was created in which GPCR-focused libraries were screened against sets of oGPCR targets, with a goal of discovering fit-for-purpose chemical probes for the more druggable members of the set. Application of the platform to a set of oGPCRs resulted in the discovery of the first reported small molecule agonists for GPR39, a receptor implicated in the regulation of insulin secretion and preservation of beta cells in the pancreas. Compound 1 stimulated intracellular calcium mobilization in recombinant and native cells in a GPR39-specific manner but did not potentiate glucose-stimulated insulin secretion in human islet preparations.

A novel series of glucagon receptor antagonists with reduced molecular weight and lipophilicity.

A novel series of glucagon receptor antagonists has been discovered. These pyrazole ethers and aminopyrazoles have lower molecular weight and increased polarity such that the molecules fall into better drug-like property space. This work has culminated in compounds 44 and 50 that were shown to have good pharmacokinetic attributes in dog, in contrast to rats, in which clearance was high; and compound 49, which demonstrated a dose-dependent reduction in glucose excursion in a rat glucagon challenge experiment.

The palladium-catalyzed aerobic kinetic resolution of secondary alcohols: reaction development, scope, and applications.

The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.

Pd-catalyzed enantioselective aerobic oxidation of secondary alcohols: applications to the total synthesis of alkaloids.

Enantioselective syntheses of the alkaloids (-)-aurantioclavine, (+)-amurensinine, (-)-lobeline, and (-)- and (+)-sedamine are described. The syntheses demonstrate the effectiveness of the Pd-catalyzed asymmetric oxidation of secondary alcohols in diverse contexts and the ability of this methodology to set the absolute configuration of multiple stereocenters in a single operation. The utility of an aryne C-C insertion reaction in accessing complex polycyclic frameworks is also described.

Synthesis of novel oxazolidinone antimicrobial agents.

The oxazolidinone class of antimicrobials represents a promising advance in the fight against resistant Gram-positive bacterial infections. Four novel oxazolidinone antimicrobial compounds, each containing a benzodioxin ring system, have been prepared. The general synthesis of each compound begins with the construction of a benzodioxin ring system containing a nitro substituent that ultimately becomes the nitrogen of the oxazolidinone ring. Three of the compounds utilize high yielding 'click chemistry' in their final step. The antimicrobial activities of the new oxazolidinones have been measured and the MIC against Staphylococcus aureus for one of the antimicrobials was determined to be 2-3 microg/mL, which is comparable to the well-known oxazolidinone, linezolid.

Catalytic enantioselective stereoablative reactions: an unexploited approach to enantioselective catalysis.

Approaches to the preparation of enantioenriched materials via catalytic methods that destroy stereogenic elements of a molecule are discussed. Although these processes often decrease overall molecular complexity, there are several notable advantages including material recycling, enantiodivergence and convergence, and increased substrate scope. Examples are accompanied by discussion of the critical design elements required for the success of these methods.

A convergent and enantioselective synthesis of (+)-amurensinine via selective C-H and C-C bond insertion reactions.

A convergent and enantioselective synthesis of the natural product amurensinine is described. The synthetic strategy takes advantage of mild and selective C-H and C-C bond insertion reactions, in addition to the palladium-catalyzed aerobic oxidative kinetic resolution recently developed in these laboratories.