Andrew K. Takle

Demonstration of a Genetic Therapeutic Index for Tumors Expressing Oncogenic BRAF by the Kinase Inhibitor SB-590885

Oncogenic BRAF alleles are both necessary and sufficient for cellular transformation, suggesting that chemical inhibition of the activated mutant protein kinase may reverse the tumor phenotype. Here, we report the characterization of SB-590885, a novel triarylimidazole that selectively inhibits Raf kinases with more potency towards B-Raf than c-Raf. Crystallographic analysis revealed that SB-590885 stabilizes the oncogenic B-Raf kinase domain in an active configuration, which is distinct from the previously reported mechanism of action of the multi-kinase inhibitor, BAY43-9006. Malignant cells expressing oncogenic B-Raf show selective inhibition of mitogen-activated protein kinase activation, proliferation, transformation, and tumorigenicity when exposed to SB-590885, whereas other cancer cell lines and normal cells display variable sensitivities or resistance to similar treatment. These studies support the validation of oncogenic B-Raf as a target for cancer therapy and provide the first evidence of a correlation between the expression of oncogenic BRAF alleles and a positive response to a selective B-Raf inhibitor.

6-Heteroaryl-pyrazolo[3,4-b]pyridines: potent and selective inhibitors of glycogen synthase kinase-3 (GSK-3)

A series of 6-heteroaryl-pyrazolo[3,4-b]pyridines has been optimised to afford potent inhibitors of Glycogen Synthase Kinase-3 (GSK-3). These analogues display excellent selectivity over the closely related Cyclin Dependent Kinase-2 (CDK-2).

Pleuromutilins. Part 1. The identification of novel mutilin 14-carbamates.

A novel series of mutilin 14-carbamates has been discovered as a result of structure-activity studies on the naturally occurring antibiotic pleuromutilin (1). In particular, the 4-methoxybenzoylcarbamate, SB-222734 (15o) displays potent antibacterial activity against a number of bacterial pathogens which are resistant to currently used agents and shows enhanced metabolic stability when compared to earlier pleuromutilin derivatives. Such derivatives therefore have the potential to provide a new class of antibacterial agents for human therapy which address the threat of bacterial resistance.

The identification of potent, selective and CNS penetrant furan-based inhibitors of B-Raf kinase

Modification of the potent imidazole-based B-Raf inhibitor SB-590885 resulted in the identification of a series of furan-based derivatives with enhanced CNS penetration. One such compound, SB-699393 (17), was examined in vivo to challenge the hypothesis that selective B-Raf inhibitors may be of value in the treatment of stroke.

Chiral oxime ethers in asymmetric synthesis. O-(1-Phenylbutyl)benzyloxyacetaldoxime, a versatile reagent for the asymmetric synthesis of protected 1,2-aminoalcohols, α-amino acid derivatives, and 2-hydroxymethyl nitrogen heterocycles including iminosugars

Addition of a range of organolithium and Grignard reagents to (E)-O-(1-phenylbutyl)benzyloxyacetaldoxime 1 in the presence of boron trifluoride diethyl etherate is highly diastereoselective. The resulting hydroxylamines undergo N-O bond cleavage upon treatment with zinc-acetic acid or molybdenum hexacarbonyl to give, after N-protection, protected 1,2-aminoalcohols 3 in high enantiomeric purity. Debenzylation of 3a and 3d gave N-Boc (R)-alaninol and (S)-phenylalaninol respectively. The hydroxylamines 2 also serve as alpha-amino acid precursors, 2i being converted into N-formyl-(R)-alaninyl-(S)-(4-bromo)phenylalanine ester 7, the N-terminal dipeptide of a natural depsipeptide. The versatility of the 1,2-aminoalcohol derivatives was further illustrated by their conversion into 5-, 6- and 7-membered 2-hydroxymethyl nitrogen heterocycles 15-19 in high enantiomeric excess by a ring-closing metathesis reaction. Further reaction of the dihydropyrrole 15 gave the iminosugar 1,4-dideoxy-1,4-imino-D-ribitol.

Asymmetric synthesis of N-protected amino acids by the addition of organolithium carboxyl synthons to ROPHy/SOPHy-derived aldoximes and ketoximes

A new asymmetric synthesis of alpha-amino acids is described in which the key step is the highly diastereoselective addition of organolithium carboxyl synthons (2-furyllithium, phenyllithium, vinyllithium) to (R)- and (S)-O-(1-phenylbutyl) oximes to give hydroxylamines, with vinyllithium being the most satisfactory nucleophilic reagent. Subsequent reductive cleavage of the N-O bond in hydroxylamines, followed by N-protection, and oxidative cleavage of the carboxyl precursor gave a range of N-protected amino acids and esters. The method was exemplified by the synthesis of a range of derivatives of non-proteinogenic amino acids such as 4-bromophenylalanine, tert-leucine, norvaline, cyclohexyl- and aryl-glycines, 2-amino-8-oxodecanoic acid (Aoda) and alpha-methylvaline.

Novel tricyclic pyrazole BRAF inhibitors with imidazole or furan central scaffolds

Graphical abstract 1j IC50 (BRAF) = 0.24 μM; IC50 (pERK) = 0.58 μM; GI50 (SRB) = 0.87 μM.

Potent achiral agonists of the growth hormone secretagogue (ghrelin) receptor. Part 2: Lead optimisation.

A series of small molecule orally bioavailable ghrelin receptor agonists have been identified through systematic optimisation of a high throughput screening hit.

Identification of clinical candidates from the benzazepine class of histamine H3 receptor antagonists.

This Letter describes the discovery of GSK189254 and GSK239512 that were progressed as clinical candidates to explore the potential of H3 receptor antagonists as novel therapies for the treatment of Alzheimers disease and other dementias. By carefully controlling the physicochemical properties of the benzazepine series and through the implementation of an aggressive and innovative screening strategy that employed high throughput in vivo assays to efficiently triage compounds, the medicinal chemistry effort was able to rapidly progress the benzazepine class of H3 antagonists through to the identification of clinical candidates with robust in vivo efficacy and excellent developability properties.

Orally active C-6 heteroaryl- and heterocyclyl-substituted imidazo[1,2-a]pyridine acid pump antagonists (APAs).

Acid pump antagonists (APAs) such as the imidazo[1,2-a]pyridine AZD-0865 2 have proven efficacious at low oral doses in acid related gastric disorders. Herein we describe some of the broader SAR in this class of molecule and detail the discovery of an imidazo[1,2-a]pyridine 15 which has excellent efficacy in animal models of gastric acid secretion following oral administration, as well as a good overall developability profile. The discovery strategy focuses on use of heteroaryl and heterocyclic substituents at the C-6 position and optimization of developability characteristics through modulation of global physico-chemical properties.