Mark Stuart Chambers

Discovery of highly potent, selective, and brain-penetrable leucine-rich repeat kinase 2 (LRRK2) small molecule inhibitors.

There is a high demand for potent, selective, and brain-penetrant small molecule inhibitors of leucine-rich repeat kinase 2 (LRRK2) to test whether inhibition of LRRK2 kinase activity is a potentially viable treatment option for Parkinsons disease patients. Herein we disclose the use of property and structure-based drug design for the optimization of highly ligand efficient aminopyrimidine lead compounds. High throughput in vivo rodent cassette pharmacokinetic studies enabled rapid validation of in vitro-in vivo correlations. Guided by this data, optimal design parameters were established. Effective incorporation of these guidelines into our molecular design process resulted in the discovery of small molecule inhibitors such as GNE-7915 (18) and 19, which possess an ideal balance of LRRK2 cellular potency, broad kinase selectivity, metabolic stability, and brain penetration across multiple species. Advancement of GNE-7915 into rodent and higher species toxicity studies enabled risk assessment for early development.

The synthesis of (+)- and (–)-epibatidine

The synthesis of the alkaloid epibatidine {exo-2-(2-chloro-5-pyridyl)-7-azabicyclo[2.2.1]heptane} in enantiomeric form involving, as the critical step, reaction or 5-lithio-2-chloropyridine with N-tert-butoxycarbonyl-7-azabicyclo[2.2.1]heptan-2-one is described.

Discovery of Highly Potent, Selective, and Brain-Penetrant Aminopyrazole Leucine-Rich Repeat Kinase 2 (LRRK2) Small Molecule Inhibitors

Leucine-rich repeat kinase 2 (LRRK2) has drawn significant interest in the neuroscience research community because it is one of the most compelling targets for a potential disease-modifying Parkinsons disease therapy. Herein, we disclose structurally diverse small molecule inhibitors suitable for assessing the implications of sustained in vivo LRRK2 inhibition. Using previously reported aminopyrazole 2 as a lead molecule, we were able to engineer structural modifications in the solvent-exposed region of the ATP-binding site that significantly improve human hepatocyte stability, rat free brain exposure, and CYP inhibition and induction liabilities. Disciplined application of established optimal CNS design parameters culminated in the rapid identification of GNE-0877 (11) and GNE-9605 (20) as highly potent and selective LRRK2 inhibitors. The demonstrated metabolic stability, brain penetration across multiple species, and selectivity of these inhibitors support their use in preclinical efficacy and safety studies.

In vitro and in vivo properties of 3-tert-butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)-pyrazolo[1,5-d]-[1,2,4]triazine (MRK-016), a GABAA receptor alpha5 subtype-selective inverse agonist

3-tert-Butyl-7-(5-methylisoxazol-3-yl)-2-(1-methyl-1H-1,2,4-triazol-5-ylmethoxy)-pyrazolo[1,5-d][1,2,4]triazine (MRK-016) is a pyrazolotriazine with an affinity of between 0.8 and 1.5 nM for the benzodiazepine binding site of native rat brain and recombinant human α1-, α2-, α3-, and α5-containing GABAA receptors. It has inverse agonist efficacy selective for the α5 subtype, and this α5 inverse agonism is greater than that of the prototypic α5-selective compound 3-(5-methylisoxazol-3-yl)-6-[(1-methyl-1,2,3-triazol-4-hdyl)methyloxy]-1,2,4-triazolo[3,4-a]phthalazine (α5IA). Consistent with its greater α5 inverse agonism, MRK-016 increased long-term potentiation in mouse hippocampal slices to a greater extent than α5IA. MRK-016 gave good receptor occupancy after oral dosing in rats, with the dose required to produce 50% occupancy being 0.39 mg/kg and a corresponding rat plasma EC50 value of 15 ng/ml that was similar to the rhesus monkey plasma EC50 value of 21 ng/ml obtained using [11C]flumazenil positron emission tomography. In normal rats, MRK-016 enhanced cognitive performance in the delayed matching-to-position version of the Morris water maze but was not anxiogenic, and in mice it was not proconvulsant and did not produce kindling. MRK-016 had a short half-life in rat, dog, and rhesus monkey (0.3–0.5 h) but had a much lower rate of turnover in human compared with rat, dog, or rhesus monkey hepatocytes. Accordingly, in human, MRK-016 had a longer half-life than in preclinical species (∼3.5 h). Although it was well tolerated in young males, with a maximal tolerated single dose of 5 mg corresponding to an estimated occupancy in the region of 75%, MRK-016 was poorly tolerated in elderly subjects, even at a dose of 0.5 mg, which, along with its variable human pharmacokinetics, precluded its further development.

An asymmetric synthesis of thiotetronic acids using chirality transfer via an allyl xanthate-to-dithiocarbonate rearrangement. X-Ray crystal structure of (5R)-2,5-dihydro-4-hydroxy-5-methyl-3-phenyl-5-prop-1′-enyl-2-oxothiophene

An asymmetric synthesis of thiotetronic acids has been developed which is based upon an allyl xanthate-to-dithiocarbonate rearrangement, the absolute configuration of the products being confirmed by an X-ray crystal structure determination.

Rapid analogue synthesis of C-5 substituted 1,2,3-triazolo-[1,5-a]quinazolines

Abstract A rapid analogue synthetic strategy has been developed to allow easy variation of the C-5 position of 1,2,3-triazolo[1,5-a]quinazolines. A range of directly linked and carbon tethered aromatic heterocyclic groups have been introduced utilising palladium catalysed cross-coupling reactions on an imino tosylate.

L-708,474: the C5-cyclohexyl analogue of L-365,260, a selective high affinity ligand for the CCKB/gastrin receptor

Abstract The C5-cyclohexyl analogue of the cholecystokinin type-B (CCKB) receptor antagonist L-365,260 has been prepared. This derivative has significantly higher CCKB affinity and markedly improved CCKB/CCKA receptor selectivity (6,500 v. 87-fold) than the parent compound. It is one of the most potent and selective CCKB ligands reported to date.

POTENT, SELECTIVE, WATER-SOLUBLE BENZODIAZEPINE-BASED CCKB RECEPTOR ANTAGONISTS THAT CONTAIN LIPOPHILIC CARBOXYLATE SURROGATES

Abstract Acylsulphonamide analogues of the meta-tolylurea L-708,474 have been synthesised and evaluated as CCKB receptor antagonists. Such derivatives retain very high affinity and subtype selectivity for the CCKB receptor, and have good aqueous solubility. The ortho-tolyl acylsulphonamide L-736,309 is orally bioavailable and brain penetrant in rat.

Discovery of a Highly Selective, Brain-Penetrant Aminopyrazole LRRK2 Inhibitor

The modulation of LRRK2 kinase activity by a selective small molecule inhibitor has been proposed as a potentially viable treatment for Parkinsons disease. By using aminopyrazoles as aniline bioisosteres, we discovered a novel series of LRRK2 inhibitors. Herein, we describe our optimization effort that resulted in the identification of a highly potent, brain-penetrant aminopyrazole LRRK2 inhibitor (18) that addressed the liabilities (e.g., poor solubility and metabolic soft spots) of our previously disclosed anilino-aminopyrimidine inhibitors. In in vivo rodent PKPD studies, 18 demonstrated good brain exposure and engendered significant reduction in brain pLRRK2 levels post-ip administration. The strategies of bioisosteric substitution of aminopyrazoles for anilines and attenuation of CYP1A2 inhibition described herein have potential applications to other drug discovery programs.

Non-covalent inhibitors of rhinovirus 3C protease

The first known non-covalent inhibitors of rhinovirus 3C protease (3CP) have been identified through fragment based screening and hit identification activities.