The discovery of VU0652957 (VU2957, Valiglurax): SAR and DMPK challenges en route to an mGlu4 PAM development candidate.

This letter describes the first account of the chemical optimization (SAR and DMPK profiling) of a new series of mGlu4 positive allosteric modulators (PAMs), leading to the identification of VU0652957 (VU2957, Valiglurax), a compound profiled as a preclinical development candidate. Here, we detail the challenges faced in allosteric modulator programs (e.g., steep SAR, as well as subtle structural changes affecting overall physiochemical/DMPK properties and CNS penetration).

The discovery of VU0486846: steep SAR from a series of M1 PAMs based on a novel benzomorpholine core.

This letter describes the chemical optimization of a new series of M1 positive allosteric modulators (PAMs) based on a novel benzomorpholine core, developed via iterative parallel synthesis, and culminating in the highly utilized rodent in vivo tool compound, VU0486846 (7), devoid of adverse effect liability. This is the first report of the optimization campaign (SAR and DMPK profiling) that led to the discovery of VU0486846 and details all of the challenges faced in allosteric modulator programs (both steep and flat SAR, as well as subtle structural changes affecting CNS penetration and overall physiochemical and DMPK properties).

Discovery and characterization of N-(1,3-dialkyl-1H-indazol-6-yl)-1H-pyrazolo[4,3-b]pyridin-3-amine scaffold as mGlu4 positive allosteric modulators that mitigate CYP1A2 induction liability.

Previous reports from our laboratory disclosed the structure and activity of a novel 1H-pyrazolo[4,3-b]pyridine-3-amine scaffold (VU8506) which showed excellent potency, selectivity and in vivo efficacy in preclinical rodent models of Parkinson's disease. Unfortunately, this compound suffered from significant CYP1A2 induction as measured through upstream AhR activation (125-fold) and thus was precluded from further advancement in chronic studies. Herein, we report a new scaffold developed recently which was systematically studied in order to mitigate the CYP1A2 liabilities presented in the earlier scaffolds. We have identified a novel structure that maintains the potency and selectivity of other mGlu4 PAMs, leading to 9i (hmGlu4 EC50 = 43 nM; AhR activation = 2.3-fold).

Further optimization of the M1 PAM VU0453595: Discovery of novel heterobicyclic core motifs with improved CNS penetration.

This Letter describes the continued chemical optimization of the VU0453595 series of M1 positive allosteric modulators (PAMs). By surveying alternative 5,6- and 6,6-heterobicylic cores for the 6,7-dihydro-5H-pyrrolo[3,4-b]pyridine-5-one core of VU453595, we found new cores that engendered not only comparable or improved M1 PAM potency, but significantly improved CNS distribution (Kps 0.3-3.1). Moreover, this campaign provided fundamentally distinct M1 PAM chemotypes, greatly expanding the available structural diversity for this valuable CNS target, devoid of hydrogen-bond donors.

Discovery of 3-aminopicolinamides as metabotropic glutamate receptor subtype 4 (mGlu4) positive allosteric modulator warheads engendering CNS exposure and in vivo efficacy.

This letter describes the further chemical optimization of the picolinamide-derived family of mGlu4 PAMs wherein we identified a 3-amino substituent to the picolinamide warhead that engendered potency, CNS penetration and in vivo efficacy. From this optimization campaign, VU0477886 emerged as a potent (EC50=95nM, 89% Glu Max) mGlu4 PAM with an attractive DMPK profile (brain:plasma Kp=1.3), rat CLp=4.0mL/min/kg, t1/2=3.7h) and robust efficacy in our standard preclinical Parkinson's disease model, haloperidol-induced catalepsy (HIC).

Discovery and SAR of muscarinic receptor subtype 1 (M1) allosteric activators from a molecular libraries high throughput screen. Part 1: 2,5-dibenzyl-2H-pyrazolo[4,3-c]quinolin-3(5H)-ones as positive allosteric modulators.

Results from a 2012 high-throughput screen of the NIH Molecular Libraries Small Molecule Repository (MLSMR) against the human muscarinic receptor subtype 1 (M1) for positive allosteric modulators is reported. A content-rich screen utilizing an intracellular calcium mobilization triple-addition protocol allowed for assessment of all three modes of pharmacology at M1, including agonist, positive allosteric modulator, and antagonist activities in a single screening platform. We disclose a dibenzyl-2H-pyrazolo[4,3-c]quinolin-3(5H)-one hit (DBPQ, CID 915409) and examine N-benzyl pharmacophore/SAR relationships versus previously reported quinolin-3(5H)-ones and isatins, including ML137. SAR and consideration of recently reported crystal structures, homology modeling, and structure-function relationships using point mutations suggests a shared binding mode orientation at the putative common allosteric binding site directed by the pendant N-benzyl substructure.

Tandem iodine-mediated oxidations of tetrahydro-ß-carbolines: total synthesis of eudistomins Y1-Y7.

An efficient iodine-mediated oxidation of tetrahydro-ß-carbolines is described to yield aromatic ß-carboline products with tandem C-H oxidation. The utility of the method was demonstrated in total syntheses of the alkaloids eudistomins Y1-Y7.

Spiroaminal Model Systems of the Marineosins with Final Step Pyrrole Incorporation.

In this Letter, we describe a short, 6-step enantioselective route to spiroaminal lactam model systems reminiscent of marineosins A and B has been developed starting from either (R)- or (S)-hydroxysuccinic acid, respectively, in ~9% overall yield. This route enables late stage incorporation of the pyrrole ring at C5 via nucleophilic displacement of an iminium triflate salt.

High-Affinity Alkynyl Bisubstrate Inhibitors of Nicotinamide N-Methyltransferase (NNMT).

Nicotinamide N-methyltransferase (NNMT) is a metabolic enzyme that methylates nicotinamide (NAM) using cofactor S-adenosylmethionine (SAM). NNMT overexpression has been linked to diabetes, obesity, and various cancers. In this work, structure-based rational design led to the development of potent and selective alkynyl bisubstrate inhibitors of NNMT. The reported nicotinamide-SAM conjugate (named NS1) features an alkyne as a key design element that closely mimics the linear, 180° transition state geometry found in the NNMT-catalyzed SAM → NAM methyl transfer reaction. NS1 was synthesized in 14 steps and found to be a high-affinity, subnanomolar NNMT inhibitor. An X-ray cocrystal structure and SAR study revealed the ability of an alkynyl linker to span the methyl transfer tunnel of NNMT with ideal shape complementarity. The compounds reported in this work represent the most potent and selective NNMT inhibitors reported to date. The rational design principle described herein could potentially be extended to other methyltransferase enzymes.

Discovery, Structure-Activity Relationship, and Biological Characterization of a Novel Series of 6-((1 H-Pyrazolo[4,3- b]pyridin-3-yl)amino)-benzo[ d]isothiazole-3-carboxamides as Positive Allosteric Modulators of the Metabotropic Glutamate Receptor 4 (mGlu4).

This work describes the discovery and characterization of novel 6-(1 H-pyrazolo[4,3- b]pyridin-3-yl)amino-benzo[ d]isothiazole-3-carboxamides as mGlu4 PAMs. This scaffold provides improved metabolic clearance and CYP1A2 profiles compared to previously discovered mGlu4 PAMs. From this work, 27o (VU6001376) was identified as a potent (EC50 = 50.1 nM, 50.5% GluMax) and selective mGlu4 PAM with an excellent rat DMPK profile ( in vivo rat CLp = 3.1 mL/min/kg, t1/2 = 445 min, CYP1A2 IC50 > 30 µM). Compound 27o was also active in reversing haloperidol induced catalepsy in a rodent preclinical model of Parkinson's disease.

Discovery of VU2957 (Valiglurax): An mGlu4 Positive Allosteric Modulator Evaluated as a Preclinical Candidate for the Treatment of Parkinson's Disease.

Herein, we report the discovery of a novel potent, selective, CNS penetrant, and orally bioavailable mGlu4 PAM, VU0652957 (VU2957, Valiglurax). VU2957 possessed attractive in vitro and in vivo pharmacological and DMPK properties across species. To advance toward the clinic, a spray-dried dispersion (SDD) formulation of VU2957 was developed to support IND-enabling toxicology studies. Based on its overall profile, VU2957 was evaluated as a preclinical development candidate for the treatment of Parkinson's disease.

Allosteric modulation of the M1 muscarinic acetylcholine receptor: improving cognition and a potential treatment for schizophrenia and Alzheimer's disease.

Allosteric modulation of AMPA, NR2B, mGlu2, mGlu5 and M1, targeting glutamatergic dysfunction, represents a significant area of research for the treatment of schizophrenia. Of these targets, clinical promise has been demonstrated using muscarinic activators for the treatment of Alzheimer's disease (AD) and schizophrenia. These diseases have inspired researchers to determine the effects of modulating cholinergic transmission in the forebrain, which is primarily regulated by one of five subtypes of muscarinic acetylcholine receptor (mAChR), a subfamily of G-protein-coupled receptors (GPCRs). Of these five subtypes, M1 is highly expressed in brain regions responsible for learning, cognition and memory. Xanomeline, an orthosteric muscarinic agonist with modest selectivity, was one of the first compounds that displayed improvements in behavioral disturbances in AD patients and efficacy in schizophrenics. Since these initial clinical results, many scientists, including those in our laboratories, have strived to elucidate the role of M1 with compounds that display improved selectivity for this receptor by targeting allosteric modes of receptor activation. A survey of selected compounds in this area will be presented.

Biomimetic synthesis and biological evaluation of Aplidiopsamine A.

The first total synthesis of Aplidiopsamine A, a rare 3H-pyrrolo[2,3-c]quinoline alkaloid from the Aplidiopsis confluata, has been achieved following the proposed biosynthesis. This biomimetic synthesis requires only five steps and proceeds in 20.8% overall yield. Biological evaluation across large panels of discrete molecular targets identified that Aplidiopsamine A is a highly selective PDE4 inhibitor, a target for numerous CNS disorders.

Room-temperature aromatization of tetrahydro-ß-carbolines by 2-iodoxybenzoic acid: utility in a total synthesis of eudistomin U.

2-Iodoxybenzoic acid is a convenient reagent for the dehydrogenation of tetrahydro-ß-carbolines to their aromatic forms under mild conditions. The utility of the method was demonstrated in a total synthesis of the marine indole alkaloid eudistomin U.

Enantioselective formal total synthesis of (+)-aspergillide C.

An enantioselective formal total synthesis of the cytotoxic macrolide (+)-aspergillide C has been accomplished from (S)-(-)-glyceraldehyde acetonide and the Danishefsky-Kitahara diene. Strategic transformations include a hetero Diels-Alder reaction, Ferrier-type addition, and palladium-catalyzed oxidative lactonization to set key stereocenters within the dihydropyran core, followed by fragment coupling via (E)-selective Julia-Kocienski olefination.