David James Rawson

The preparation of enantiomerically enriched γ-amino acids (GABAs) using palladium catalysed allylic substitution

Abstract Enantioselective palladium catalysed allylic substitution reactions have been employed as the asymmetry-producing step in the synthesis of enantiomerically enriched γ-amino acids.

Design and pharmacological evaluation of PF-4840154, a non-electrophilic reference agonist of the TrpA1 channel.

TrpA1 is an ion channel involved in nociceptive and inflammatory pain. It is implicated in the detection of chemical irritants through covalent binding to a cysteine-rich intracellular region of the protein. While performing an HTS of the Pfizer chemical collection, a class of pyrimidines emerged as a non-reactive, non-covalently binding family of agonists of the rat and human TrpA1 channel. Given the issues identified with the reference agonist Mustard Oil (MO) in screening, a new, non-covalently binding agonist was optimized and proved to be a superior agent to MO for screening purposes. Compound 16a (PF-4840154) is a potent, selective agonist of the rat and human TrpA1 channel and elicited TrpA1-mediated nocifensive behaviour in mouse.

Discovery and Optimization of Selective Nav1.8 Modulator Series That Demonstrate Efficacy in Preclinical Models of Pain

Voltage-gated sodium channels, in particular Nav1.8, can be targeted for the treatment of neuropathic and inflammatory pain. Herein, we described the optimization of Nav1.8 modulator series to deliver subtype selective, state, and use-dependent chemical matter that is efficacious in preclinical models of neuropathic and inflammatory pain.

The discovery of UK-369003, a novel PDE5 inhibitor with the potential for oral bioavailability and dose-proportional pharmacokinetics

This paper describes our recent efforts to design and synthesise potent and selective PDE5 inhibitors and the use of in vitro predictors of clearance, absorption and permeability to maximise the potential for dose-proportional pharmacokinetics and good oral bioavailability in man. Optimisation of the preclinical profile resulted in the identification of UK-369003 (19a) and its nomination as a clinical candidate. The clinical pharmacokinetic and safety profile has enabled us to progress the compound to test its efficacy in patients with lower urinary tract symptoms (LUTS) associated with benign prostatic hyperplasia (BPH) and a paper describing its efficacy has recently been published.

Discovery of Clinical Candidate 4-[2-(5-Amino-1H-pyrazol-4-yl)-4-chlorophenoxy]-5-chloro-2-fluoro-N-1,3-thiazol-4-ylbenzenesulfonamide (PF-05089771): Design and Optimization of Diaryl Ether Aryl Sulfonamides as Selective Inhibitors of NaV1.7

A series of acidic diaryl ether heterocyclic sulfonamides that are potent and subtype selective NaV1.7 inhibitors is described. Optimization of early lead matter focused on removal of structural alerts, improving metabolic stability and reducing cytochrome P450 inhibition driven drug-drug interaction concerns to deliver the desired balance of preclinical in vitro properties. Concerns over nonmetabolic routes of clearance, variable clearance in preclinical species, and subsequent low confidence human pharmacokinetic predictions led to the decision to conduct a human microdose study to determine clinical pharmacokinetics. The design strategies and results from preclinical PK and clinical human microdose PK data are described leading to the discovery of the first subtype selective NaV1.7 inhibitor clinical candidate PF-05089771 (34) which binds to a site in the voltage sensing domain.

Part 3: Design and synthesis of proline-derived α2δ ligands

A potent series of substituted (2S,4S)-benzylproline α(2)δ ligands have been designed from the readily available starting material (2S,4R)-hydroxy-L-proline. The ligands have improved pharmacokinetic profile over the (4S)-phenoxyproline derivatives described previously and have potential for development as oral agents for the treatment of neuropathic pain. Compound 16 has been progressed to clinical development.

Highly potent and selective NaV1.7 inhibitors for use as intravenous agents and chemical probes

The discovery and selection of a highly potent and selective NaV1.7 inhibitor PF-06456384, designed specifically for intravenous infusion, is disclosed. Extensive in vitro pharmacology and ADME profiling followed by in vivo preclinical PK and efficacy model data are discussed. A proposed protein-ligand binding mode for this compound is also provided to rationalise the high levels of potency and selectivity over inhibition of related sodium channels. To further support the proposed binding mode, potent conjugates are described which illustrate the potential for development of chemical probes to enable further target evaluation.

Part 2: Design, synthesis and evaluation of hydroxyproline-derived α2δ ligands

Conformational constraint has been used to design a potent series of α(2)δ ligands derived from the readily available starting material (2S,4R)-hydroxy-l-proline. The ligands have improved physicochemistry and potency compared to their linear counterparts (described in our earlier publication) and the lead compound has been progressed to clinical development.

The Design and Synthesis of a Novel, Orally Active, Selective ETA Antagonist

The potency and pharmacokinetic properties of an indole-based series of endothelin antagonists have been optimised using in vitro, in silico and in vivo methods. Compound 8 is oxidised in vivo to the active metabolite 7 and has been highlighted as an orally active agent suitable for further profiling. A synthesis of the active enantiomer of the lead compound (8a) and its metabolite (7a) has been developed and the pharmacokinetic and pharmacological profiles of 8a are presented.

Part 1: N-Alkylated glycines as potent α2δ ligands

A new series of glycine-derived ligands of the α(2)δ subunit of voltage gated calcium channels is described. Several novel compounds (7) based on (6) were prepared that possessed a potency <100 nM in the α(2)δ binding assay.