Christopher Blackburn

Parallel synthesis of 3-aminoimidazo[1,2-a]pyridines and pyrazines by a new three-component condensation

Abstract A three-component condensation reaction between 2-aminopyridine, an aldehyde and an isonitrile catalyzed by scandium triflate affords derivatives of 3-aminoimidazo[1,2-a]pyridine; aminopyrazine reacts similarly. A library of heterocycles, prepared in high yield by parallel synthesis and purification on an ion-exchange resin, was subjected to further reactions at the amino group.

A three-component solid-phase synthesis of 3-aminoimidazo[1,2-a]azines

Abstract The three-component condensation between a 2-aminoazine, an aldehyde and an isonitrile catalyzed by scandium triflate was conducted on a solid support with any of the three reacting functional groups tethered to Rink amide resin via an appropriate bifunctional carboxylic acid. The resulting resin-bound 3-aminoimidaz[1,2-a]azines could be efficiently acylated prior to cleavage.

Characterization of a new series of non-covalent proteasome inhibitors with exquisite potency and selectivity for the 20S β5-subunit

The mammalian 26S proteasome is a 2500 kDa multi-catalytic complex involved in intracellular protein degradation. We describe the synthesis and properties of a novel series of non-covalent di-peptide inhibitors of the proteasome used on a capped tri-peptide that was first identified by high-throughput screening of a library of approx. 350000 compounds for inhibitors of the ubiquitin–proteasome system in cells. We show that these compounds are entirely selective for the β5 (chymotrypsin-like) site over the β1 (caspase-like) and β2 (trypsin-like) sites of the 20S core particle of the proteasome, and over a panel of less closely related proteases. Compound optimization, guided by X-ray crystallography of the liganded 20S core particle, confirmed their non-covalent binding mode and provided a structural basis for their enhanced in vitro and cellular potencies. We demonstrate that such compounds show low nanomolar IC50 values for the human 20S β5 site in vitro, and that pharmacological inhibition of this site in cells is sufficient to potently inhibit the degradation of a tetra-ubiquitin–luciferase reporter, activation of NFκB (nuclear factor κB) in response to TNF-α (tumour necrosis factor-α) and the proliferation of cancer cells. Finally, we identified capped di-peptides that show differential selectivity for the β5 site of the constitutively expressed proteasome and immunoproteasome in vitro and in B-cell lymphomas. Collectively, these studies describe the synthesis, activity and binding mode of a new series of non-covalent proteasome inhibitors with unprecedented potency and selectivity for the β5 site, and which can discriminate between the constitutive proteasome and immunoproteasome in vitro and in cells.The mammalian 26S proteasome is a 2500 kDa multi-catalytic complex involved in intracellular protein degradation. We describe the synthesis and properties of a novel series of non-covalent di-peptide inhibitors of the proteasome based [corrected] on a capped tri-peptide that was first identified by high-throughput screening of a library of approx. 350000 compounds for inhibitors of the ubiquitin-proteasome system in cells. We show that these compounds are entirely selective for the beta5 (chymotrypsin-like) site over the beta1 (caspase-like) and beta2 (trypsin-like) sites of the 20S core particle of the proteasome, and over a panel of less closely related proteases. Compound optimization, guided by X-ray crystallography of the liganded 20S core particle, confirmed their non-covalent binding mode and provided a structural basis for their enhanced in vitro and cellular potencies. We demonstrate that such compounds show low nanomolar IC50 values for the human 20S beta5 site in vitro, and that pharmacological inhibition of this site in cells is sufficient to potently inhibit the degradation of a tetra-ubiquitin-luciferase reporter, activation of NFkappaB (nuclear factor kappaB) in response to TNF-alpha (tumour necrosis factor-alpha) and the proliferation of cancer cells. Finally, we identified capped di-peptides that show differential selectivity for the beta5 site of the constitutively expressed proteasome and immunoproteasome in vitro and in B-cell lymphomas. Collectively, these studies describe the synthesis, activity and binding mode of a new series of non-covalent proteasome inhibitors with unprecedented potency and selectivity for the beta5 site, and which can discriminate between the constitutive proteasome and immunoproteasome in vitro and in cells.

A novel dealkylation affording 3-aminoimidazo[1,2-a]pyridines: access to new substitution patterns by solid-phase synthesis†

Abstract The three-component synthesis of 3-aminoimidazo[1,2- a ]pyridine derivatives has been extended by a novel acid-induced dealkyation reaction that removes the 1,1,3,3-tetramethylbutyl group derived from the isonitrile input. This reaction was conducted on the solid-phase using the HMBA linker and the resulting products subjected to reductive alkylation using several aldehydes, thereby accessing novel substitution patterns at the 3-position.

“High‐load” polyethylene glycol–polystyrene (PEG–PS) graft supports for solid‐phase synthesis

The choice of a polymeric support is a key factor for the success of solid‐phase methods for syntheses of organic compounds and biomolecules such as peptides and oligonucleotides. Classical Merrifield solid‐phase peptide synthesis (SPPS), performed on low cross‐linked hydrophobic polystyrene (PS) beads, sometimes suffers from sequence‐dependent coupling difficulties. The concept of incorporating polyethylene glycol (PEG) into supports for solid‐phase synthesis represents a successful approach to alleviating such problems. Previous reports from our laboratories have shown the advantages of “low‐load” PEG–PS (0.15–0.25 mmol/g) for SPPS. Herein, we demonstrate that the beneficial aspects of the PEG–PS concept can be extended with resins that have higher loadings (0.3–0.5 mmol/g).

SOLID-PHASE SYNTHESIS OF CYCLIC HOMODETIC PEPTIDES

Publisher Summary This chapter discusses solid-phase synthesis of cyclic homodetic peptides. It reviews the synthesis of cyclic homodetic peptides by solid-phase methods with an emphasis on solid supports, protecting group strategy, reagents, side reactions, and the emergence of cyclic peptide combinatorial libraries. There are two general classes of cyclic peptides: (1) homodetic and (2) heterodetic. Ring formation may occur to form the amide linkage between an amino and carboxylic acid function to give homodetic cyclic peptides, whereas any other linkages such as lactone, ether, thioether, and, most commonly, the disulfide bridge are referred to as heterodetic. Cyclic hexapeptides containing a proline to further restrict conformational possibilities were prepared and extensively studied. With the development of improved synthetic methods, larger ring sizes and more intriguing targets have been successfully attempted.

Optimization of a series of dipeptides with a P3 threonine residue as non-covalent inhibitors of the chymotrypsin-like activity of the human 20S proteasome.

Starting from a tripeptide screening hit, a series of dipeptide inhibitors of the proteasome with Thr as the P3 residue has been optimized with the aid of crystal structures in complex with the β-5/6 active site of y20S. Derivative 25, (β5 IC(50)=7.4 nM) inhibits only the chymotryptic activity of the proteasome, shows cellular activity against targets in the UPS, and inhibits proliferation.

Design and Optimization of Potent and Orally Bioavailable Tetrahydronaphthalene Raf Inhibitors

Inhibition of mutant B-Raf signaling, through either direct inhibition of the enzyme or inhibition of MEK, the direct substrate of Raf, has been demonstrated preclinically to inhibit tumor growth. Very recently, treatment of B-Raf mutant melanoma patients with a selective B-Raf inhibitor has resulted in promising preliminary evidence of antitumor activity. This article describes the design and optimization of tetrahydronaphthalene-derived compounds as potent inhibitors of the Raf pathway in vitro and in vivo. These compounds possess good pharmacokinetic properties in rodents and inhibit B-Raf mutant tumor growth in mouse xenograft models.

Discovery and optimization of N-acyl and N-aroylpyrazolines as B-Raf kinase inhibitors.

A high throughput screen identified N-aroylpyrazoline 1 as a selective inhibitor of the V600E mutant of B-Raf kinase. Parallel synthesis of acyl, aroyl, and sulfonyl derivatives led to the identification of several potent inhibitors in both enzymatic and cellular (pERK) assays such as compound 42.

N,C-Capped Dipeptides with Selectivity for Mycobacterial Proteasome over Human Proteasomes: Role of S3 and S1 Binding Pockets

We identified N,C-capped dipeptides that are selective for the Mycobacterium tuberculosis proteasome over human constitutive and immunoproteasomes. Differences in the S3 and S1 binding pockets appeared to account for the species selectivity. The inhibitors can penetrate mycobacteria and kill nonreplicating M. tuberculosis under nitrosative stress.