Association of respiratory failure with inhibition of NaV1.6 in the phrenic nerve

As part of a drug discovery effort to identify potent inhibitors of NaV1.7 for the treatment of pain, we observed that inhibitors produced unexpected cardiovascular and respiratory effects in vivo. Specifically, inhibitors administered to rodents produced changes in cardiovascular parameters and respiratory cessation. We sought to determine the mechanism of the in vivo adverse effects by studying the selectivity of the compounds on NaV1.5, NaV1.4, and NaV1.6 in in vitro and ex vivo assays. Inhibitors lacking sufficient NaV1.7 selectivity over NaV1.6 were associated with respiratory cessation after in vivo administration to rodents. Effects on respiratory rate in rats were consistent with effects in an ex vivo hemisected rat diaphragm model and in vitro NaV1.6 potency. Furthermore, direct blockade of the phrenic nerve signaling was observed at exposures known to cause respiratory cessation in rats. Collectively, these results support a significant role for NaV1.6 in phrenic nerve signaling and respiratory function.

Optimization and Mechanistic Investigations of Novel Allosteric Activators of PKG1α

Activation of PKG1α is a compelling strategy for the treatment of cardiovascular diseases. As the main effector of cyclic guanosine monophosphate (cGMP), activation of PKG1α induces smooth muscle relaxation in blood vessels, lowers pulmonary blood pressure, prevents platelet aggregation, and protects against cardiac stress. The development of activators has been mostly limited to cGMP mimetics and synthetic peptides. Described herein is the optimization of a piperidine series of small molecules to yield activators that demonstrate in vitro phosphorylation of vasodilator-stimulated phosphoprotein as well as antiproliferative effects in human pulmonary arterial smooth muscle cells. Hydrogen/deuterium exchange mass spectrometry experiments with the small molecule activators revealed a mechanism of action consistent with cGMP-induced activation, and an X-ray co-crystal structure with a construct encompassing the regulatory domains illustrated a binding mode in an allosteric pocket proximal to the low-affinity cyclic nucleotide-binding domain.

Nav1.7 target modulation and efficacy can be measured in nonhuman primate assays

Humans with loss-of-function mutations in the Na_v1.7 channel gene (SCN9A) show profound insensitivity to pain, whereas those with gain-of-function mutations can have inherited pain syndromes. Therefore, inhibition of the Na_v1.7 channel with a small molecule has been considered a promising approach for the treatment of various human pain conditions. To date, clinical studies conducted using selective Na_v1.7 inhibitors have not provided analgesic efficacy sufficient to warrant further investment. Clinical studies to date used multiples of in vitro IC₅₀ values derived from electrophysiological studies to calculate anticipated human doses. To increase the chance of clinical success, we developed rhesus macaque models of action potential propagation, nociception, and olfaction, to measure Na_v1.7 target modulation in vivo. The potent and selective Na_v1.7 inhibitors SSCI-1 and SSCI-2 dose-dependently blocked C-fiber nociceptor conduction in microneurography studies and inhibited withdrawal responses to noxious heat in rhesus monkeys. Pharmacological Na_v1.7 inhibition also reduced odor-induced activation of the olfactory bulb (OB), measured by functional magnetic resonance imaging (fMRI) studies consistent with the anosmia reported in Na_v1.7 loss-of-function patients. These data demonstrate that it is possible to measure Na_v1.7 target modulation in rhesus macaques and determine the plasma concentration required to produce a predetermined level of inhibition. The calculated plasma concentration for preclinical efficacy could be used to guide human efficacious exposure estimates. Given the translatable nature of the assays used, it is anticipated that they can be also used in phase 1 clinical studies to measure target modulation and aid in the interpretation of phase 1 clinical data.

Discovery of Arylsulfonamide Nav1.7 Inhibitors: IVIVC, MPO Methods, and Optimization of Selectivity Profile

The voltage-gated sodium channel Nav1.7 continues to be a high-profile target for the treatment of various pain afflictions due to its strong human genetic validation. While isoform selective molecules have been discovered and advanced into the clinic, to date, this target has yet to bear fruit in the form of marketed therapeutics for the treatment of pain. Lead optimization efforts over the past decade have focused on selectivity over Nav1.5 due to its link to cardiac side effects as well as the translation of preclinical efficacy to man. Inhibition of Nav1.6 was recently reported to yield potential respiratory side effects preclinically, and this finding necessitated a modified target selectivity profile. Herein, we report the continued optimization of a novel series of arylsulfonamide Nav1.7 inhibitors to afford improved selectivity over Nav1.6 while maintaining rodent oral bioavailability through the use of a novel multiparameter optimization (MPO) paradigm. We also report in vitro-in vivo correlations from Nav1.7 electrophysiology protocols to preclinical models of efficacy to assist in projecting clinical doses. These efforts produced inhibitors such as compound 19 with potency against Nav1.7, selectivity over Nav1.5 and Nav1.6, and efficacy in behavioral models of pain in rodents as well as inhibition of rhesus olfactory response indicative of target modulation.

Subminute micro-isolation of pharmaceuticals with ultra-high pressure liquid chromatography

The drive for faster separations while maintaining quality and yield remains an important consideration for enhanced productivity as well as cost reduction for drug discovery laboratories in the pharmaceutical industry. High-throughput experimentation (HTE) and high-throughput screening (HTS) techniques can benefit from rapid and efficient isolation of product at high purity and recovery from microgram-scale crude reaction mixtures. In this study we describe the isolation of small molecule and biomolecule crude mixtures at the microgram-scale (100-2500 μg) in single or library format with methods as fast as 1.0 min and system pressures averaging 10,000 psi with an ultra-high pressure liquid chromatography (UHPLC) setup. UHPLC technology provides several advantages for rapid (<1.0 min) separations with small-particle (1.8-3.5 μm) size 4.6 × 50 mm C18 columns such as minimal extra column and delay volume, fast detector response time, and higher linear velocities for improved speed and resolution. We typically see a 5-10 fold improvement in purification time and overall sample processing time with low fraction volumes and same-day drying when compared with traditional semi-preparative techniques. There is a significant 50-fold reduction in solvent usage per run, resulting in a much lower cost of solvent and waste handling. Fluidic pathways have been optimized for collection into tared high-density 96 or 384 well 2D barcoded storage tubes in a microtiter plate (MTP) layout. Coupling the system to robotics has enabled us to implement a fully integrated automation platform with additional capabilities for small-scale purification at high speed and reduced cost of materials. The resulting arrays of small-quantity, high-purity compounds enable synthetic route scouting for HTE and HTS for biological target validation.

MK-7622: A First-in-Class M1 Positive Allosteric Modulator Development Candidate

Identification of ligands that selectively activate the M₁ muscarinic signaling pathway has been sought for decades to treat a range of neurological and cognitive disorders. Herein, we describe the optimization efforts focused on addressing key physicochemical and safety properties, ultimately leading to the clinical candidate MK-7622, a highly selective positive allosteric modulator of the M₁ muscarinic receptor that has entered Phase II studies in patients with Alzheimer's disease.

Discovery of a 3-(4-Pyrimidinyl) Indazole (MLi-2), an Orally Available and Selective Leucine-Rich Repeat Kinase 2 (LRRK2) Inhibitor that Reduces Brain Kinase Activity

Leucine-rich repeat kinase 2 (LRRK2) is a large, multidomain protein which contains a kinase domain and GTPase domain among other regions. Individuals possessing gain of function mutations in the kinase domain such as the most prevalent G2019S mutation have been associated with an increased risk for the development of Parkinson's disease (PD). Given this genetic validation for inhibition of LRRK2 kinase activity as a potential means of affecting disease progression, our team set out to develop LRRK2 inhibitors to test this hypothesis. A high throughput screen of our compound collection afforded a number of promising indazole leads which were truncated in order to identify a minimum pharmacophore. Further optimization of these indazoles led to the development of MLi-2 (1): a potent, highly selective, orally available, brain-penetrant inhibitor of LRRK2.

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.

Biosynthetic studies of the notoamides: isotopic synthesis of stephacidin A and incorporation into notoamide B and sclerotiamide

The advanced natural product stephacidin A is proposed as a biosynthetic precursor to notoamide B in various Aspergillus species. Doubly (13)C-labeled racemic stephacidin A was synthesized and fed to cultures of the terrestrial-derived fungus, Aspergillus versicolor NRRL 35600, and the marine-derived fungus, Aspergillus sp. MF297-2. Analysis of the metabolites revealed enantiospecific incorporation of intact (-)-stephacidin A into (+)-notoamide B in Aspergillus versicolor and (+)-stephacidin A into (-)-notoamide B in Aspergillus sp. MF297-2. (13)C-Labeled sclerotiamide was also isolated from both fungal cultures.

Discovery of a selective allosteric M1 receptor modulator with suitable development properties based on a quinolizidinone carboxylic acid scaffold

One approach to ameliorate the cognitive decline in Alzheimer's disease (AD) has been to restore neuronal signaling from the basal forebrain cholinergic system via the activation of the M(1) muscarinic receptor. A number of nonselective M(1) muscarinic agonists have previously shown positive effects on cognitive behaviors in AD patients, but were limited due to cholinergic adverse events thought to be mediated by the activation of the M(2) to M(5) subtypes. One strategy to confer selectivity for M(1) is the identification of positive allosteric modulators, which would target an allosteric site on the M(1) receptor rather than the highly conserved orthosteric acetylcholine binding site. Quinoline carboxylic acids have been previously identified as highly selective M(1) positive allosteric modulators with good pharmacokinetic and in vivo properties. Herein is described the optimization of a novel quinolizidinone carboxylic acid scaffold with 4-cyanopiperidines being a key discovery in terms of enhanced activity. In particular, modulator 4i gave high plasma free fractions, enhanced central nervous system (CNS) exposure, was efficacious in a rodent in vivo model of cognition, and afforded good physicochemical properties suitable for further preclinical evaluation.

Genome-based characterization of two prenylation steps in the assembly of the stephacidin and notoamide anticancer agents in a marine-derived Aspergillus sp

Stephacidin and notoamide natural products belong to a group of prenylated indole alkaloids containing a core bicyclo[2.2.2]diazaoctane ring system. These bioactive fungal secondary metabolites have a range of unusual structural and stereochemical features but their biosynthesis has remained uncharacterized. Herein, we report the first biosynthetic gene cluster for this class of fungal alkaloids based on whole genome sequencing of a marine-derived Aspergillus sp. Two central pathway enzymes catalyzing both normal and reverse prenyltransfer reactions were characterized in detail. Our results establish the early steps for creation of the prenylated indole alkaloid structure and suggest a scheme for the biosynthesis of stephacidin and notoamide metabolites. The work provides the first genetic and biochemical insights for understanding the structural diversity of this important family of fungal alkaloids.

Synthetic Studies on Palau'amine. Construction of the Cyclopentane Core via an Asymmetric 1,3-Dipolar Cycloaddition

The cyclopentane core of palau'amine has been constructed in optically pure form through the use of an asymmetric azomethine ylid [1,3]-dipolar cycloaddition reaction.

Synthesis and conformation-activity relationships of the peptide isosteres of FK228 and largazole

The peptide isosteres (10 and 11) of the naturally occurring and potent histone deacetylase (HDAC) inhibitors FK228 and largazole have been synthesized and evaluated side-by-side with FK228, largazole, and SAHA for inhibition of the class I HDACs 1, 2, 3, and 6.

Isolation of notoamide E, a key precursor in the biosynthesis of prenylated indole alkaloids in a marine-derived fungus, Aspergillus sp

Notoamide E was identified to be a short-lived precursor in the biosynthesis of prenylated indole alkaloids in the mussel-derived Aspergillus sp. In addition, the feeding experiment of the (13)C-labeled notoamide E afforded structurally novel metabolites.

Isolation of antipodal (-)-versicolamide B and notoamides L-N from a marine-derived Aspergillus sp

Antipodal (-)-versicolamide B and notoamides L-N were isolated from a marine-derived Aspergillus sp. The possible biosynthetic pathway of enantiomeric pairs of notoamide B and versicolamide B are proposed. Notoamide L is the first metabolite containing 25 carbons in the related prenylated indole alkaloids. Notoamide M is potentially a precursor to the proposed azadiene species involved in the putative intramolecular Diels-Alder reaction in the biogenesis of the bicyclo[2.2.2]diazaoctane ring system.

Calmodulin inhibitory activity of the malbrancheamides and various analogs

The preparation and biological activity of various structural analogs of the malbrancheamides are disclosed. The impact of indole chlorination, C-12a relative stereochemistry, and bicyclo[2.2.2]diazaoctane core oxidation state on the ability of these analogs to inhibit calmodulin dependent phosphodiesterase (PDE1) was studied, and a number of potent compounds were identified.

Premalbrancheamide: synthesis, isotopic labeling, biosynthetic incorporation, and detection in cultures of Malbranchea aurantiaca

An advanced metabolite, named premalbrancheamide, involved in the biosynthesis of malbrancheamide (1) and malbrancheamide B (2) has been synthesized in double (13)C-labeled form and was incorporated into the indole alkaloid 2 by Malbranchea aurantiaca. In addition, premalbrancheamide has been detected as a natural metabolite in cultures of M. aurantiaca. The biosynthetic implications of these experiments are discussed.

Detection of VM55599 and preparaherquamide from Aspergillus japonicus and Penicillium fellutanum: biosynthetic implications

The secondary metabolites VM55599 (4) and preparaherquamide (5) have been identified by LC-MS(n) analysis as natural metabolites in cultures of Penicillium fellutanum, whereas preparaherquamide has been identified only in cultures of Aspergillus japonicus. In accord with a previous proposal, the identification of both metabolites, which have a diastereomeric relationship, provides indirect support for a unified biosynthetic scheme.

Biomimetic total synthesis of malbrancheamide and malbrancheamide B

The biomimetic total syntheses of both malbrancheamide and malbrancheamide B are reported. The synthesis of the two monochloro species enabled the structure of malbrancheamide B to be unambiguously assigned. The syntheses each feature an intramolecular Diels-Alder reaction of a 5-hydroxypyrazin-2(1H)-one to construct the bicyclo[2.2.2]diazaoctane core, which has also been proposed as the biosynthetic route to these compounds.

Improved total synthesis of the potent HDAC inhibitor FK228 (FR-901228)

A scaleable synthesis of the potent histone deacetylase (HDAC) inhibitor FK228 is described. A reliable strategy for preparing the key beta-hydroxy mercapto heptenoic acid partner was accomplished in nine steps and 13% overall yield. A Noyori asymmetric hydrogen-transfer reaction established the hydroxyl stereochemistry in >99:1 er via the reduction of a propargylic ketone.

Synthesis of indoles via 6pi-electrocyclic ring closures of trienecarbamates

A new method for the preparation of indoles from readily available alpha-haloenones and alpha-(trialkylstannyl)enecarbamates is described. Following a Stille coupling, trienecarbamate 2 is electronically activated to undergo a facile 6pi-electrocyclic ring closure and subsequent oxidation to afford protected aniline 4. Upon deprotection and reductive amination, acid 5 underwent clean cyclization to N-acetylindole 6 (Ac2O, NEt3, 130 degrees C). This method has been used to construct a variety of substituted indoles that are not easily prepared by conventional indole annelation methods.

Improved Biomimetic Total Synthesis of d,l-Stephacidin A

The direct conversion of beta-hydroxyproline derivatives into 5-hydroxypyrazin-2(1H)-ones under Mitsunobu conditions has been discovered to be a general biomimetic protocol generating IMDA intermediates and has been applied to the concise, biomimetic total syntheses of D,L-stephacidin A and D,L-brevianamide B.

Concise, Biomimetic Total Synthesis of d,l-Marcfortine C

A biomimetic total synthesis of the fungal metabolite marcfortine C utilizing an intramolecular Diels-Alder reaction is described. In addition, a key stereoselective oxaziridine-mediated oxidation/pinacol rearrangement of indole 24 was used to complete the total synthesis.

An approach to the total synthesis of welwistatin

An approach to the total synthesis of the antimicrotubule agent welwistatin is described. Key transformations include (1) a 7-endo intramolecular conjugate addition reaction of enone 6 to deliver the strained bicyclo[4.3.1]decanone 5; (2) a 6pi electrocyclic ring closure of trienecarbamate 16 followed by oxidation to afford protected aniline 17; and (3) an intramolecular cyclization of acetic acid derivative 18 to give rise to indole 19. [reaction: see text]

6-Bromomethyl-4H-1,3-dioxin: a versatile bromomethyl vinyl ketone equivalent for heterocycle and carbocycle construction

6-Bromomethyl-4H-1,3-dioxin has been prepared in three steps from allyl iodide. A variety of enolates were then alkylated with this bromide. The resulting 6-alkyl-4H-1,3-dioxins were either subjected to further multistep transformations and/or heated to effect facile retrocycloaddition reactions. The resulting enones smoothly participated in novel endo-conjugate addition reactions with both carbon and nitrogen nucleophiles. For example, several bicyclo[4.3.1]decan-3,10-diones, the carbon framework of the CP compounds, were constructed using this novel annulation strategy. In another natural product study, a benzazocine related to the heterocyclic framework of the ring-opened tautomeric form of FR-900482 was also prepared using this methodology. Finally, a piperidin-4-one obtained from a 6-endo conjugate addition was converted to the naturally occurring (2S,4R)-4-hydroxypipecolic acid. Collectively, these examples document the synthetic equivalency of dioxin 1 with bromomethyl vinyl ketone and, moreover, delineate a strategy for accomplishing the sequential reactions with nucleophiles at the alpha' followed by the beta electrophilic sites.

Total synthesis of (+/-)-lepadiformine via an amidoacrolein cycloaddition

[reaction: see text]. The total synthesis of the cytotoxin lepadiformine is described. The intermolecular cycloaddition of a 2-amidoacrolein with the dimethyl acetal of 4,6-heptadienal gave a cycloadduct that was strategically functionalized for elaboration of the tricyclic ring system. These steps include a diastereoselective addition of an organoytterbium reagent to an aldehyde, cyclization to the trans-perhydroquinoline substructure via a Mitsunobu reaction, and an iodine-promoted amine cyclization with an alkene to introduce the pyrrolidine ring.