Synthesis of heteroaromatic compounds by oxidative aromatization using an activated carbon/molecular oxygen system

Recent development of imidazole derivatives as potential anticancer agents

Cancer, one of the key health problems globally, is a group of related diseases that share a number of characteristics primarily the uncontrolled growth and invasive to surrounding tissues. Chemotherapy is one of the ways for the treatment of cancer which uses one or more anticancer agents as per chemotherapy regimen. Limitations of most anticancer drugs due to a variety of reasons such as serious side effects, drug resistance, lack of sensitivity and efficacy etc. generate the necessity towards the designing of novel anticancer lead molecules. In this regard, the synthesis of biologically active heterocyclic molecules is an appealing research area. Among heterocyclic compounds, nitrogen containing heterocyclic molecules has fascinated tremendous consideration due to broad range of pharmaceutical activity. Imidazoles, extensively present in natural products as well as synthetic molecules, have two nitrogen atoms, and are five membered heterocyclic rings. Because of their countless physiological and pharmacological characteristics, medicinal chemists are enthused to design and synthesize new imidazole derivatives with improved pharmacodynamic and pharmacokinetic properties. The aim of this present chapter is to discuss the synthesis, chemistry, pharmacological activity, and scope of imidazole-based molecules in anticancer drug development. Finally, we have discussed the current challenges and future perspectives of imidazole-based derivatives in anticancer drug development.

Reduced Graphene Oxides as Carbocatalysts in Acceptorless Dehydrogenation of N-Heterocycles

The catalytic properties of graphene-derived materials are evaluated in acceptorless dehydrogenation of N-heterocycles. Among them, reduced graphene oxides (rGOs) are active (quantitative yields in 23 h) under mild conditions (130 °C) and act as efficient heterogeneous carbocatalysts. rGO exhibits reusability and stability at least during eight consecutive runs. Mechanistic investigations supported by experimental evidence (i.e., organic molecules as model compounds, purposely addition of metal impurities and selective functional group masking experiments) suggest a preferential contribution of ketone carbonyl groups as active sites for this transformation.

Rhodium-Catalyzed Oxidative Annulation of 2- or 7-Arylindoles with Alkenes/Alkynes Using Molecular Oxygen as the Sole Oxidant Enabled by Quaternary Ammonium Salt

Developing an efficient catalytic system using molecular oxygen as the oxidant for rhodium-catalyzed cross-dehydrogenative coupling remains highly desirable. Herein, rhodium-catalyzed oxidative annulation of 2- or 7-phenyl-1H-indoles with alkenes or alkynes to assemble valuable 6H-isoindolo[2,1-a]indoles, pyrrolo[3,2,1-de]phenanthridines, or indolo[2,1-a]isoquinolines using the atmospheric pressure of air as the sole oxidant enabled by quaternary ammonium salt has been accomplished. Mechanistic studies provided evidence for the fast intramolecular aza-Michael reaction and aerobic reoxidation of Rh(I)/Rh(III), facilitated by the addition of quaternary ammonium salt.

Direct N-heterocyclization of hydrazines to access styrylated pyrazoles: synthesis of 1,3,5-trisubstituted pyrazoles and dihydropyrazoles

A microwave-assisted method has been developed for the synthesis of tri-substituted pyrazoles via direct N-heterocyclization of hydrazines with metal-acetylacetonate and -dibenzylideneacetonate without using any base or additives. Most importantly, the synthesis of 1-aryl-5-phenyl-3-styryl-1H-pyrazoles was achieved in a single step using hydrochloride salt of various phenylhydrazines and this is the first report for direct construction of these molecules. The reaction medium and microwave conditions play a critical role for their selective product formation during the reaction. The present reaction explored the usage of metal-diketonic complexes as reaction substrates providing acetylacetone and dibenzylideneacetone moieties to directly participate in cyclization with hydrazines to form the corresponding pyrazoles in excellent yields. The present protocol introduces the important N-heterocyclic moieties in the final structures, giving the reaction great applications from a medicinal chemistry perspective, particularly in the late stage modification strategies in drug discovery.

Synthesis of a molecularly defined single-active site heterogeneous catalyst for selective oxidation of N-heterocycles

Generally, a homogeneous catalyst exhibits good activity and defined active sites but it is difficult to recycle. Meanwhile, a heterogeneous catalyst can easily be reused but its active site is difficult to reveal. It is interesting to bridge the gap between homogeneous and heterogeneous catalysis via controllable construction of a heterogeneous catalyst containing defined active sites. Here, we report that a molecularly defined, single-active site heterogeneous catalyst has been designed and prepared via the oxidative polymerization of maleimide derivatives. These polymaleimide derivatives can be active catalysts for the selective oxidation of heterocyclic compounds to quinoline and indole via the recycling of -C=O and -C-OH groups, which was confirmed by tracing the reaction with GC-MS using maleimide as the catalyst and by FT-IR analysis with polymaleimide as the catalyst. These results might promote the development of heterogeneous catalysts with molecularly defined single active sites exhibiting a comparable activity to homogeneous catalysts.

Combating Enhanced Intracellular Survival (Eis)-Mediated Kanamycin Resistance of Mycobacterium tuberculosis by Novel Pyrrolo[1,5-a]pyrazine-Based Eis Inhibitors

Tuberculosis (TB) remains one of the leading causes of mortality worldwide. Hence, the identification of highly effective antitubercular drugs with novel modes of action is crucial. In this paper, we report the discovery and development of pyrrolo[1,5-a]pyrazine-based analogues as highly potent inhibitors of the Mycobacterium tuberculosis (Mtb) acetyltransferase enhanced intracellular survival (Eis), whose up-regulation causes clinically observed resistance to the aminoglycoside (AG) antibiotic kanamycin A (KAN). We performed a structure-activity relationship (SAR) study to optimize these compounds as potent Eis inhibitors both against purified enzyme and in mycobacterial cells. A crystal structure of Eis in complex with one of the most potent inhibitors reveals that the compound is bound to Eis in the AG binding pocket, serving as the structural basis for the SAR. These Eis inhibitors have no observed cytotoxicity to mammalian cells and are promising leads for the development of innovative AG adjuvant therapies against drug-resistant TB.

Combating Enhanced Intracellular Survival (Eis)-Mediated Kanamycin Resistance of Mycobacterium tuberculosis by Novel Pyrrolo[1,5-a]pyrazine-Based Eis Inhibitors

Tuberculosis (TB) remains one of the leading causes of mortality worldwide. Hence, the identification of highly effective antitubercular drugs with novel modes of action is crucial. In this paper, we report the discovery and development of pyrrolo[1,5-a]pyrazine-based analogues as highly potent inhibitors of the Mycobacterium tuberculosis (Mtb) acetyltransferase enhanced intracellular survival (Eis), whose up-regulation causes clinically observed resistance to the aminoglycoside (AG) antibiotic kanamycin A (KAN). We performed a structure-activity relationship (SAR) study to optimize these compounds as potent Eis inhibitors both against purified enzyme and in mycobacterial cells. A crystal structure of Eis in complex with one of the most potent inhibitors reveals that the compound is bound to Eis in the AG binding pocket, serving as the structural basis for the SAR. These Eis inhibitors have no observed cytotoxicity to mammalian cells and are promising leads for the development of innovative AG adjuvant therapies against drug-resistant TB.

Radical Addition of Hydrazones by α-Bromo Ketones To Prepare 1,3,5-Trisubstituted Pyrazoles via Visible Light Catalysis

A novel efficient tandem reaction of hydrazones and α-bromo ketones is reported for the preparation of 1,3,5-trisubstituted pyrazoles by visible light catalysis. In this system, the monosubstituted hydrazones show wonderful reaction activity with alkyl radicals, generated from α-bromo ketones. A radical addition followed by intramolecular cyclization affords the important pyrazole skeleton in good to excellent yields. This efficient strategy under mild conditions with wide group tolerance provides a potential approach to the 1,3,5-trisubstituted pyrazoles.

One-pot metal-free synthesis of highly substituted pyrroles from 2-acetyl-3-methylene-1,4-dicarbonyl compounds and primary amines via TBHP and activated carbon oxidative aromatization of dihydropyrrole

A metal-free cascade process for the synthesis of highly substituted pyrroles with high yields and broad substrate tolerance via enamine, aza-Michael addition and TBHP, activated carbon oxidative aromatization is reported.

Facile synthesis of 4-O-β-N-acetylchitooligosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone based on the transformation of chitooligosaccharide and its suppressive effects against the furylfuramide-induced SOS response

A facile synthesis method is described for transforming the reducing-end residue of chitooligosaccharides (DP 2-4) into lactone. The desired 4-O-β-N-acetylchitooligosyl lactones (GN(n)L) were conveniently prepared from chitooligosaccharides by consecutive dehydration and oxidation reactions to afford 4-O-β-tri-N-acetylchitotriosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone (GN(3)L), 4-O-β-di-N-acetylchitobiosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone (GN(2)L), and 4-O-β-2-acetamido-2-deoxy-D-glucopyranosyl 2-acetamido-2,3-dideoxydidehydro-gluconolactone (GNL). The resulting lactone derivatives exhibited considerable suppression (42.6-54.3% at a concentration of 400 µM) in umu gene expression of the SOS response in Salmonella typhimurium TA1535/pSK1002 against the mutagen, 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamido (AF-2). Lactonization of the chitooligosaccharides was found to be essential for their suppression of the SOS-inducing activity.