Synthesis of novel 3,4-diaryl-5-aminopyrazoles as potential kinase inhibitors

Bisindolyl Maleimides and Indolylmaleimide Derivatives-A Review of Their Synthesis and Bioactivity

The evolution of bisindolyl maleimides and indolyl maleimide derivatives and their unique biological activities have stimulated great interest in medicinal chemistry programs. Bisindolylmaleimide (BIM)-type compounds arise from natural sources such as arcyriarubin and are biosynthetically related to indolocarbazoles. BIMs are commonly the immediate synthetic precursors of indolocarbazoles, lacking a central bond between the two aromatic units and making them more flexible and drug-like. Synthetic endeavours within this class of compounds are broad and have led to the development of both remarkably potent and selective protein kinase inhibitors. Clinical BIM examples include ruboxistaurin and enzastaurin, which are highly active inhibitors of protein kinase C-β. While BIMs are widely recognised as protein kinase inhibitors, other modes of activity have been reported, including the inhibition of calcium signalling and antimicrobial activity. Critically, structural differences can be used to exploit new bioactivity and therefore it is imperative to discover new chemical entities to address new targets. BIMs can be highly functionalised or chemically manipulated, which provides the opportunity to generate new derivatives with unique biological profiles. This review will collate new synthetic approaches to BIM-type compounds and their associated bioactivities with a focus on clinical applications.

Tailor-Made Amino Acids in Pharmaceutical Industry: Synthetic Approaches to Aza-Tryptophan Derivatives

Over the recent years there has been a noticeable upsurge of interest in aza-analogs of tryptophan which are isosteric to the latter and found numerous applications in medicinal, bioorganic chemistry, and peptide research. In the present review article, five aza-tryptophan derivatives are profiled, including aza-substitution in the positions 2, on the five-membered ring, as well as in positions 4, 5, 6, and 7 on the six-membered ring. A detailed and comprehensive literature overview of the synthetic methods for the preparation of these aza-tryptophans is presented and general facets of the biological properties and most promising applications are discussed.

Tris(pentafluorophenyl)borane-Catalyzed Formal Cyanoalkylation of Indoles with Cyanohydrins

Despite the significant achievements related to the C3 functionalization of indoles, cyanoalkylation reactions continue to remain rather limited. We herein report on the formal C3 cyanoalkylation of indoles with cyanohydrins in the presence of a tris(pentafluorophenyl)borane (B(C₆F₅)₃) catalyst. It is noteworthy that cyanohydrins are used as a cyanoalkylating reagent in the present reaction, even though they are usually used as only a HCN source. Mechanistic investigations revealed the unique reactivity of the B(C₆F₅)₃ catalyst in promoting the decomposition of a cyanohydrin by a Lewis acidic activation through the coordination of the cyano group to the boron center. In addition, a catalytic three-component reaction using indoles, aldehydes as a carbon unit, and acetone cyanohydrin that avoids the discrete preparation of each aldehyde-derived cyanohydrin is also reported. The developed methods provide straightforward, highly efficient, and atom-economic access to various types of synthetically useful indole-3-acetonitrile derivatives containing α-tertiary or quaternary carbon centers.

Tryptamine Synthesis by Iron Porphyrin Catalyzed C-H Functionalization of Indoles with Diazoacetonitrile

The functionalization of C-H bonds with non-precious metal catalysts is an important research area for the development of efficient and sustainable processes. Herein, we describe the development of iron porphyrin catalyzed reactions of diazoacetonitrile with N-heterocycles yielding important precursors of tryptamines, along with experimental mechanistic studies and proof-of-concept studies of an enzymatic process with YfeX enzyme. By using readily available FeTPPCl, we achieved the highly efficient C-H functionalization of indole and indazole heterocycles. These transformations feature mild reaction conditions, excellent yields with broad functional group tolerance, can be conducted on gram scale, and thus provide a unique streamlined access to tryptamines.

N-Acetyl-3-aminopyrazoles block the non-canonical NF-kB cascade by selectively inhibiting NIK

NF-κB-inducing kinase (NIK), an oncogenic drug target that is associated with various cancers, is a central signalling component of the non-canonical pathway. A blind screening process, which established that amino pyrazole related scaffolds have an effect on IKKbeta, led to a hit-to-lead optimization process that identified the aminopyrazole 3a as a low μM selective NIK inhibitor. Compound 3a effectively inhibited the NIK-dependent activation of the NF-κB pathway in tumour cells, confirming its selective inhibitory profile.

Reductive ortho C–H cyanoalkylation of aryl(heteroaryl) sulfoxides: a general approach to α-aryl(heteroaryl) nitriles

A catalyst-free low-temperature cyanoalkylation has been developed as a general protocol for the synthesis of α-aryl(heteroaryl) nitriles.

Synthesis and Antiproliferative Activity of Novel Heterocyclic Indole-Trimethoxyphenyl Conjugates

The synthesis and biological evaluation of a series of novel heterocyclic indole derivatives is described. The consolidation of the combretastatin and bisindolylmaleimide templates towards the inclusion of a novel heterocyclic ring proffered a versatile pharmacophore with which to pursue chemical diversification. Given literature precedent, maleimide was initially investigated in this role and the bioactivity assessed by measurement of NCI-60 cell panel growth. Subsequently, a range of 5-aminopyrazoles was designed and developed to explore the specific effect of heterocycle hydrogen bonding on cell growth. The unique electronic nature of the 5-aminopyrazole moiety allowed for regiospecific monosubstitution on different sites of the ring, such as thiourea substitution at the N(1) position for derivative 45 or trifluoroacetylation on the 5-amino position for 43. Further derivatisation led to the ultimate development of bicyclic pyrazolotriazinedione 41 and pyrimidine 42 systems. The antiproliferative activities of these 3,4-diaryl-5-aminopyrazoles were assessed using the NCI-60 cell screen, disclosing the discovery of distinct selectivity profiles towards a number of cell lines, such as SNB-75 CNS cancer, UO-31 and CAKI-1 renal cancer cells. A series of DNA topological assays discounted the interaction with topoisomerase II as a putative mechanism of action.

Enantioselective Model Synthesis and Progress toward the Putative Structure of Yuremamine

An enantioselective model synthesis of the 2,3-dihydro-1H-pyrrolo[1,2-a]indole core of the putative structure of yuremamine is reported in 39% overall yield and 96% ee over five steps. The model synthesis leverages enantioselective, rhodium-catalyzed hydroacylation of an N-vinylindole-2-carboxaldehyde as the key step in the installation of the stereochemical triad. An enantioselective synthesis of a densely functionalized dihydropyrroloindolone that maps onto the putative structure of yuremamine is demonstrated in 26% yield and 97% ee over eight steps.

Biosynthesis of Violacein, Structure and Function of l-Tryptophan Oxidase VioA from Chromobacterium violaceum

Violacein is a natural purple pigment of Chromobacterium violaceum with potential medical applications as antimicrobial, antiviral, and anticancer drugs. The initial step of violacein biosynthesis is the oxidative conversion of l-tryptophan into the corresponding α-imine catalyzed by the flavoenzyme l-tryptophan oxidase (VioA). A substrate-related (3-(1H-indol-3-yl)-2-methylpropanoic acid) and a product-related (2-(1H-indol-3-ylmethyl)prop-2-enoic acid) competitive VioA inhibitor was synthesized for subsequent kinetic and x-ray crystallographic investigations. Structures of the binary VioA·FADH2 and of the ternary VioA·FADH2·2-(1H-indol-3-ylmethyl)prop-2-enoic acid complex were resolved. VioA forms a "loosely associated" homodimer as indicated by small-angle x-ray scattering experiments. VioA belongs to the glutathione reductase family 2 of FAD-dependent oxidoreductases according to the structurally conserved cofactor binding domain. The substrate-binding domain of VioA is mainly responsible for the specific recognition of l-tryptophan. Other canonical amino acids were efficiently discriminated with a minor conversion of l-phenylalanine. Furthermore, 7-aza-tryptophan, 1-methyl-tryptophan, 5-methyl-tryptophan, and 5-fluoro-tryptophan were efficient substrates of VioA. The ternary product-related VioA structure indicated involvement of protein domain movement during enzyme catalysis. Extensive structure-based mutagenesis in combination with enzyme kinetics (using l-tryptophan and substrate analogs) identified Arg(64), Lys(269), and Tyr(309) as key catalytic residues of VioA. An increased enzyme activity of protein variant H163A in the presence of l-phenylalanine indicated a functional role of His(163) in substrate binding. The combined structural and mutational analyses lead to the detailed understanding of VioA substrate recognition. Related strategies for the in vivo synthesis of novel violacein derivatives are discussed.

Synthesis and identification of novel indolo[2,3-a]pyrimido[5,4-c]carbazoles as a new class of anti-cancer agents

A range of 5,6-bisindole and 5-indole-6-(7-azaindole)pyrimidinones were synthesised via a β-keto ester intermediate and a screen of cyclisation conditions undertaken. The optimised route to this new class of indolocarbazoles and azaindolocarbazoles involved photocyclisation, with typical yields of 50-60%. These derivatives were screened for anti-cancer activity via topo II inhibition and the NCI-60 cell line assay, with the screening indicating a lack of topo II inhibition, but significant in vitro growth inhibition within this new chemical class, in the low micromolar range against renal cancer, melanoma and colon cancer cell lines.