Pharmacological validation of dihydrofolate reductase as a drug target in Mycobacterium abscessus.

The Mycobacterium abscessus drug development pipeline is poorly populated, with particularly few validated target-lead couples to initiate de novo drug discovery. Trimethoprim, an inhibitor of dihydrofolate reductase (DHFR) used for the treatment of a range of bacterial infections, is not active against M. abscessus. Thus, evidence that M. abscessus DHFR is vulnerable to pharmacological intervention with a small molecule inhibitor is lacking. Here, we show that the pyrrolo-quinazoline PQD-1, previously identified as a DHFR inhibitor active against Mycobacterium tuberculosis, exerts whole cell activity against M. abscessus. Enzyme inhibition studies showed that PQD-1, in contrast to trimethoprim, is a potent inhibitor of M. abscessus DHFR and over-expression of DHFR causes resistance to PQD-1, providing biochemical and genetic evidence that DHFR is a vulnerable target and mediates PQD-1's growth inhibitory activity in M. abscessus. As observed in M. tuberculosis, PQD-1 resistant mutations mapped to the folate pathway enzyme thymidylate synthase (TYMS) ThyA. Like trimethoprim in other bacteria, PQD-1 synergizes with the dihydropteroate synthase (DHPS) inhibitor sulfamethoxazole (SMX), offering an opportunity to exploit the successful dual inhibition of the folate pathway and develop similarly potent combinations against M. abscessus. PQD-1 is active against subspecies of M. abscessus and a panel of clinical isolates, providing epidemiological validation of the target-lead couple. Leveraging a series of PQD-1 analogs, we have demonstrated a dynamic structure-activity relationship (SAR). Collectively, the results identify M. abscessus DHFR as an attractive target and PQD-1 as a chemical starting point for the discovery of novel drugs and drug combinations that target the folate pathway in M. abscessus.

Activity of Tricyclic Pyrrolopyrimidine Gyrase B Inhibitor against Mycobacterium abscessus.

Tricyclic pyrrolopyrimidines (TPPs) are a new class of antibacterials inhibiting the ATPase of DNA gyrase. TPP8, a representative of this class, is active against Mycobacterium abscessus in vitro. Spontaneous TPP8 resistance mutations mapped to the ATPase domain of M. abscessus DNA gyrase, and the compound inhibited DNA supercoiling activity of recombinant M. abscessus enzyme. Further profiling of TPP8 in macrophage and mouse infection studies demonstrated proof-of-concept activity against M. abscessus ex vivo and in vivo.

Analgesia and peripheral c-fiber modulation by selective Nav1.8 inhibition in rhesus.

ABSTRACT: Voltage-gated sodium (Nav) channels present untapped therapeutic value for better and safer pain medications. The Nav1.8 channel isoform is of particular interest because of its location on peripheral pain fibers and demonstrated role in rodent preclinical pain and neurophysiological assays. To-date, no inhibitors of this channel have been approved as drugs for treating painful conditions in human, possibly because of challenges in developing a sufficiently selective drug-like molecule with necessary potency not only in human but also across preclinical species critical to the preclinical development path of drug discovery. In addition, the relevance of rodent pain assays to the human condition is under increasing scrutiny as a number of mechanisms (or at the very least molecules) that are active in rodents have not translated to humans, and direct impact on pain fibers has not been confirmed in vivo. In this report, we have leveraged numerous physiological end points in nonhuman primates to evaluate the analgesic and pharmacodynamic activity of a novel, potent, and selective Nav1.8 inhibitor compound, MSD199. These pharmacodynamic biomarkers provide important confirmation of the in vivo impact of Nav1.8 inhibition on peripheral pain fibers in primates and have high translational potential to the clinical setting. These findings may thus greatly improve success of translational drug discovery efforts toward better and safer pain medications, as well as the understanding of primate biology of Nav1.8 inhibition broadly.

Discovery of [11C]MK-8056: A Selective PET Imaging Agent for the Study of mGluR2 Negative Allosteric Modulators.

Modification of potent, selective metabotropic glutamate receptor 2 negative allosteric modulator (mGluR2 NAM) led to a series of analogues with excellent binding affinity, lipophilicity, and suitable physicochemical properties for a PET tracer with convenient chemical handles for incorporation of a 11C or 18F radiolabel. [11C]MK-8056 was synthesized and evaluated in vivo and demonstrated appropriate affinity, selectivity, and physicochemical properties to be used as a positron emission tomography tracer for mGluR2.

Discovery of MK-8768, a Potent and Selective mGluR2 Negative Allosteric Modulator.

Glutamate plays a key role in cognition and mood, and it has been shown that inhibiting ionotropic glutamate receptors disrupts cognition, while enhancing ionotropic receptor activity is pro-cognitive. One approach to elevating glutamatergic tone has been to antagonize presynaptic metabotropic glutamate receptor 2 (mGluR2). A desire for selectivity over the largely homologous mGluR3 motivated a strategy to achieve selectivity through the identification of mGluR2 negative allosteric modulators (NAMs). Extensive screening and optimization efforts led to the identification of a novel series of 4-arylquinoline-2-carboxamides. This series was optimized for mGluR2 NAM potency, clean off-target activity, and desirable physical properties, which resulted in the identification of improved C4 and C7 substituents. The initial lead compound from this series was Ames-positive in a single strain with metabolic activation, indicating that a reactive metabolite was likely responsible for the genetic toxicity. Metabolic profiling and Ames assessment across multiple analogs identified key structure-activity relationships associated with Ames positivity. Further optimization led to the Ames-negative mGluR2 negative allosteric modulator MK-8768.

Discovery of selective glucocorticoid receptor modulator MK-5932.

A series of partial agonists of the Glucocorticoid Receptor were prepared targeting reduced transactivation activity, while maintaining significant transrepression activity. Incorporation of an ortho-aryl amide produced compounds with the desired in vitro profile. Bioreactors consisting of Suspension cultures of Sf21 cells co expressing a CYP3A4 and NADPH-cytochrome P450 oxireductase were used to prepare the major metabolites of these compounds and revealed that oxidative N-dealkylation provided a pathway for formation of metabolites that were more agonistic than the parent partial agonists. Oxidative N-dealkylation was blocked in a new series of compounds, however oxidation alone was capable of producing full agonist metabolites. Incorporation of an ortho-primary amide and utilization of fluorine to modulate agonism afforded partial agonist MK-5932. Synthesis of the major metabolites of MK-5932 using bioreactor technology revealed that no significant GR-active metabolites were formed. Orally administered MK-5932 displayed anti-inflammatory efficacy in a Rat Oxazolone-induced chronic dermatitis model, while sparing plasma insulin.

Stereoselective olefin isomerization leading to asymmetric quaternary carbon construction.

Chemo- and stereoselective Ir(I)-catalyzed isomerization of 1,1-disubstituted and trisubstituted allylic ethers and in situ [3,3] sigmatropic rearrangement of the resulting allyl vinyl ethers provide for the highly stereoselective construction of quaternary carbon stereocenters. The olefin isomerization-Claisen rearrangement (ICR) sequence allows adjacent quaternary-tertiary stereocenter relationships to be established with excellent diastereoselection. Several complementary strategies for enantioselective quaternary carbon synthesis derive directly from the ICR reaction design.

Design and Synthesis of Piperazine Sulfonamide Cores Leading to Highly Potent HIV-1 Protease Inhibitors.

Using the HIV-1 protease binding mode of MK-8718 and PL-100 as inspiration, a novel aspartate binding bicyclic piperazine sulfonamide core was designed and synthesized. The resulting HIV-1 protease inhibitor containing this core showed an 60-fold increase in enzyme binding affinity and a 10-fold increase in antiviral activity relative to MK-8718.

Discovery of MK-8718, an HIV Protease Inhibitor Containing a Novel Morpholine Aspartate Binding Group.

A novel HIV protease inhibitor was designed using a morpholine core as the aspartate binding group. Analysis of the crystal structure of the initial lead bound to HIV protease enabled optimization of enzyme potency and antiviral activity. This afforded a series of potent orally bioavailable inhibitors of which MK-8718 was identified as a compound with a favorable overall profile.

First total synthesis of the 7,3'-linked naphthylisoquinoline alkaloid ancistrocladidine.

[structure: see text] The first total synthesis of the rare 7,3'-linked naphthylisoquinoline alkaloid, ancistrocladidine, has been completed. The key feature of the synthesis is the formation of the extremely hindered biaryl linkage by Pinhey-Barton ortho-arylation of a naphthol with an aryllead triacetate. The biaryl aldehyde formed is elaborated in 10 steps to form a 1:1 mixture of ancistrocladidine and its atropisomer. Recrystallization of the mixture afforded ancistrocladidine, which was identical in all respects to the reported data.

The preclinical efficacy, selectivity and pharmacologic profile of MK-5932, an insulin-sparing selective glucocorticoid receptor modulator.

Glucocorticoids are used widely in the treatment of inflammatory diseases, but use is accompanied by a significant burden of adverse effects. It has been hypothesized that gene- and cell-specific regulation of the glucocorticoid receptor by small molecule ligands could be translated into a therapeutic with an improved risk-benefit profile. MK-5932 is a highly selective glucocorticoid receptor modulator that is anti-inflammatory in vivo with an improved profile on glucose metabolism: Bungard et al. (2011). Bioorg. Med. Chem. 19, 7374-7386. Here we describe the full biological profile of MK-5932. Cytokine production following lipopolysaccharide (LPS) challenge was blocked by MK-5932 in both rat and human whole blood. Oral administration reduced inflammatory cytokine levels in the serum of rats challenged with LPS. MK-5932 was anti-inflammatory in a rat contact dermatitis model, but was differentiated from 6-methylprednisolone by a lack of elevation of fasting insulin or glucose levels after 7 days of dosing, even at high exposure levels. In fact, animals in the vehicle group were consistently hyperglycemic at the end of the study, and MK-5932 normalized glucose levels in a dose-dependent manner. MK-5932 was also anti-inflammatory in the rat collagen-induced arthritis and adjuvant-induced arthritis models. In healthy dogs, oral administration of MK-5932 exerted acute pharmacodynamic effects with potency comparable to prednisone, but with important differences on neutrophil counts, again suggestive of a dissociated profile. Important gaps in our understanding of mechanism of action remain, but MK-5932 will be a useful tool in dissecting the mechanisms of glucose dysregulation by therapeutic glucocortiocids.

Total synthesis of the 7,3'-linked naphthylisoquinoline alkaloid ancistrocladidine.

The first total synthesis of ancistrocladidine, a rare 7,3'-linked naphthylisoquinoline alkaloid, has been completed, with the key feature of the synthesis being the formation of the extremely hindered biaryl linkage by ortho-arylation of a naphthol with an aryllead triacetate. Initial efforts were focused on the generation of a heteroaryl lead species, which would have allowed a convergent synthesis to be developed. However, it was not possible to generate such a lead species. A simpler aryl lead triacetate was prepared and reacted. The resulting biaryl aldehyde was elaborated in 10 steps to form a 1:1 mixture of ancistrocladidine and its atropisomer. Recrystallization of the mixture afforded ancistrocladidine, which was identical in all respects to the reported data.

Strategies for expanding structural diversity available from olefin isomerization-claisen rearrangement reactions.

Boron-substituted di(allyl) ethers provide an efficient conduit for expanding the structural diversity available from olefin isomerization-Claisen rearrangement (ICR) reactions. Easily prepared allyl propargyl ethers undergo chemoselective Zr(IV)-catalyzed hydroboration to afford the boron-substituted ICR substrates. The boron-substituted allyl residue undergoes chemoselective Ir(I)-catalyzed olefin isomerization and in situ Claisen rearrangement to afford stereodefined beta-boryl aldehyde products. Functionalization of the C-B linkage by oxidation or Suzuki cross-coupling provides a route to Claisen adducts previously inaccessible from the ICR methodology.

A convenient preparation of functionalized 1,8-dioxygenated naphthalenes from 6-alkoxybenzocyclobutenones.

An alternate route for the synthesis of naphthalene building blocks 1-4 has been developed, starting from readily available 6-alkoxybenzocyclobutenones. As thermolysis of a propynylbenzocyclobutenol only provided the naphthalene in low yield, allenyl-substituted benzocyclobutenols were investigated. The desired allenic precursors were prepared by a two-step procedure, which involved hydroxyl-directed reduction of the chloropropargylbenzocyclobutenols obtained from addition of lithiopropargyl chloride to the benzocyclobutenones. Thermolysis of the allenic alcohols gave the desired naphthalenes in good yields.

Catalyzed olefin isomerization leading to highly stereoselective Claisen rearrangements of aliphatic allyl vinyl ethers.

Iridium(I)-catalyzed olefin isomerization in bis(allyl) ethers is integrated into a generally applicable strategy for affecting highly stereoselective Claisen rearrangements. Catalyzed alkene isomerization affords allyl vinyl ethers from easily prepared di(allyl) ethers; direct thermolysis of these reaction mixtures leads to highly diastereoselective [3,3] sigmatropic rearrangements affording syn-2,3-dialkyl-4-pentenal derivatives. An easily executed strategy for realizing asymmetric variants of the isomerization-Claisen rearrangement (ICR) reactions is also described.