Microwave-mediated heterocyclization to benzimidazo[2,1-b]quinazolin-12(5H)-ones

Divergent Approach for Regioselective Synthesis of Linearly and Angularly Fused Benzoimidazoquinazolinones from Isatoic Anhydrides

Ph₃P-I₂-mediated condensation reactions of isatoic anhydrides and o-phenylenediamines have been developed for the regioselective syntheses of a wide range of linearly and angularly fused benzoimidazoquinazolinones. The selectivity of the products relies on the generation of either highly electrophilic oxyphosphonium or less reactive imidate intermediates. A direct amine attack at the C-2 position of the oxyphosphonium intermediate presumably drives the reaction toward the linearly fused products, whereas an attack of the diamine at the C-4 position of the in situ generated cyclic imidate leads to the angularly fused derivatives. This strategy serves as a practical handle for the efficient synthesis of other related heterocycles.

Construction of Binuclear Benzimidazole-Fused Quinazolinones and Pyrimidinones Using Aryl Isocyanates as Building Blocks by Transition-Metal-Free C(sp2)-N Coupling

A class of binuclear N-fused hybrid scaffolds was constructed by the reaction of 2-(2-bromoaryl)- and 2-(2-bromovinyl)benzimidazoles with aryl isocyanates as building blocks in the presence of a base under microwave irradiation. A nucleophilic addition followed by an unprecedented transition-metal-free C(sp²)-N coupling is proposed as a reaction pathway of this green process.

Microwave-assisted efficient one-pot synthesis of N 2-(tetrazol-5-yl)-6-aryl/heteroaryl-5,6-dihydro-1,3,5-triazine-2,4-diamines

An efficient one-pot synthesis of N 2-(tetrazol-5-yl)-6-aryl/heteroaryl-1,3,5-triazine-2,4-diamine derivatives was developed by reacting 5-amino-1,2,3,4-tetrazole with aromatic aldehydes and cyanamide in pyridine under controlled microwave heating with high yields. X-ray crystallography confirmed the structure of the obtained products.

The construction of fluorophoric thiazolo-[2,3-b]quinazolinone derivatives: a multicomponent domino synthetic approach

Acid-mediated one-pot domino reactions of substituted 2-amino thiazoles, substituted benzaldehydes and cyclic diketones have been developed for the synthesis of novel and architecturally unique thiazolo[2,3-b]quinazolinone derivatives under microwave irradiation. In this protocol, a series of thiazolo[2,3-b]quinazolinone derivatives have been synthesized and the excellent fluorescence behaviors of some of the molecules have been reported based on the incorporation of different electron-donating and electron-withdrawing substituents on the aryl moieties of the target molecules.

A library of unique fluorophoric thiazolo[2,3-b]quinazolinones were synthesized under acid catalyzed one pot microwave irradiation technique.

Traceless Solid-Phase Organic Synthesis

Traceless solid-phase synthesis represents an ultimate sophisticated synthetic strategy on insoluble supports. Compounds synthesized on solid supports can be released without a trace of the linker that was used to tether the intermediates during the synthesis. Thus, the target products are composed only of the components (atoms, functional groups) inherent to the target core structure. A wide variety of synthetic strategies have been developed to prepare products in a traceless manner, and this review is dedicated to all aspects of traceless solid-phase organic synthesis. Importantly, the synthesis does not need to be carried out on a linker designed for traceless synthesis; most of the synthetic approaches described herein were developed using standard, commercially available linkers (originally devised for solid-phase peptide synthesis). The type of structure prepared in a traceless fashion is not restricted. The individual synthetic approaches are divided into eight sections, each devoted to a different methodology for traceless synthesis. Each section consists of a brief outline of the synthetic strategy followed by a description of individual reported syntheses.

Synthesis, Characterization and Biological Evaluation of 3'-Benzoyl-5'-(Furan-2-yl)-4'-Phenylspiro[Indoline-3,2'-Pyrrolidin]-2-One Derivatives and its Molecular Docking Studies

A series of new spirooxindole derivatives were synthesized via 1,3 –dipolar cycloaddition. All the synthesized compounds were evaluated for antimicrobial activity. In antibacterial studies compound 4d demonstrated the most potent inhibitory activity (MIC = 12.5 lg/mL for K.pneumonia, B.cereus and S.typhi), which was compared with the positive control streptomycin. In antifungal studies compound 4e demonstrated the most potent inhibitory activity (MIC = 3.125 lg/mL for C.albicans and A.niger), which was related with the standard drug ketaconazole. In addition, molecular modeling studies were also performed to disclose the binding modes of the most active inhibitors to the amino acid residues that compose the active site of the glucosamine-6-phosphate synthase and crystal structure of human lanosterol 14-alpha dimethylase in complex with ketaconazole enzyme.

Metal-free C(sp2)–H functionalization of azoles: K2CO3/I2-mediated oxidation, imination, and amination

We report metal-free one-pot C2−H oxidation, imination, and amination of several azoles from azolium salts by using a commercially available simple and efficient reagent combination K₂CO₃/I₂.

1,3-Dipolar Cycloaddition Reactions for the Synthesis of Novel Oxindole Derivatives and Their Cytotoxic Properties

The multicomponent reaction between isatin, amino acid, but-2-ynedioates, and phenacyl bromide has been developed using microwave irradiation under catalyst and base-free conditions in aqueous medium. This synthetic protocol is useful for the synthesis of various functionalized spirooxindole derivatives. This MCR exhibits a broad substrate scope with excellent yields and shorter reaction time. Additionally the synthesized spirooxindole derivatives were evaluated for their anticancer activity against three human cancer cell lines: MCF-7 (breast), A549 (lung), and HeLa cervical. Most of the compounds showed moderate to potent cytotoxic activity against the tested cell lines.

An efficient and catalyst-free synthesis of N-arylidene-2-arylimidazo[1,2-a]pyridine-3-ylamine derivatives via Strecker reaction under controlled microwave heating

An efficient one-pot multicomponent reaction of 2-aminopyridine with aromatic aldehydes and either benzoyl cyanide or cyanamide in pyridine under controlled microwave heating afforded N-aryldene-2-arylimidazo[1,2-a]-pyridine-3-ylamine derivatives. The reaction is catalyst free and is of high atom economy.

An expedient microwave assisted regio- and stereoselective synthesis of spiroquinoxaline pyrrolizine derivatives and their AChE inhibitory activity

We report here an efficient protocol for the one-pot facile synthesis of spiro[indeno[1,2-b]quinoxaline-11,3′-pyrrolizine]heterocyclic scaffolds and their AChE inhibitory studies.

A Novel Mechanistic Study on Ultrasound-Assisted, One-Pot Synthesis of Functionalized Benzimidazo[2,1-b]quinazolin-1(1H)-ones

Ultrasound-assisted synthesis of benzimidazo[2,1-b]quinazolin-1(1H)-ones was achieved via piperidine-catalyzed three-component reaction of 2-aminobenzimidazoles, an aromatic aldehyde, and 1,3-dione in aqueous isopropanol. This mechanism was first suspected following our identification of unusual reaction intermediates in a one-pot reaction. An unprecedented coupling reaction, it involved a nucleophilic attack by 2-aminobenzimidazole on in situ generated Michael adduct, followed by electrocyclic ring formation reaction. In contrast to the commonly accepted mechanism, that the direct reaction of 2-amino benzimidazole with a Knoevenagel adduct cannot deliver target compounds.

A convenient and rapid microwave-assisted synthesis of spirooxindoles in aqueous medium and their antimicrobial activities

An efficient, regioselective and diastereoselective synthesis of diversely functionalized spirooxindoles under microwave irradiation in aqueous medium; most of the compounds show significant antimicrobial activities.

A copper-catalyzed multi-component reaction accessing fused imidazo-heterocycles via C–H functionalization

An efficient synthesis of fused imidazo-heterocycles is described using Cu(OTf)₂ in [bmim]BF₄ by the multi-component reaction of pyridin-2(1H)-one or thiazol/benzo[d]thiazol-2(3H)-ones with O-tosylhydroxyl amine and acetophenones under microwave irradiation.

Enaminonitriles in heterocyclic synthesis: a route to 1,3-diaryl-4-aminopyrazole derivatives

Benzylcyanide and 4-nitrobenzylcyanide condensed with triethyl orthoformate and piperidine or morpholine to yield 2-aryl-2-piperidinyl or 2-morpholinylacrylonitriles. These coupled with aromatic diazonium salts to yield the 2-arylhydrazno-2-arylethane nitriles in good yields. The latter were converted into 4-aminopyrazoles in good yields using the Thorpe-Ziegler cyclization.

Halogenated benzimidazole carboxamides target integrin alpha4beta1 on T-cell and B-cell lymphomas

Integrin alpha(4)beta(1) is an attractive but poorly understood target for selective diagnosis and treatment of T-cell and B-cell lymphomas. This report focuses on the rapid microwave preparation, structure-activity relationships, and biological evaluation of medicinally pertinent benzimidazole heterocycles as integrin alpha(4)beta(1) antagonists. We documented tumor uptake of derivatives labeled with (125)I in xenograft murine models of B-cell lymphoma. Molecular homology models of integrin alpha(4)beta(1) predicted that docked halobenzimidazole carboxamides have the halogen atom in a suitable orientation for halogen-hydrogen bonding. The high-affinity halogenated ligands identified offer attractive tools for medicinal and biological use, including fluoro and iodo derivatives with potential radiodiagnostic ((18)F) or radiotherapeutic ((131)I) applications, or chloro and bromo analogues that could provide structural insights into integrin-ligand interactions through photoaffinity, cross-linking/mass spectroscopy, and X-ray crystallographic studies.

Generation of 500-member library of 10-alkyl-2-R(1),3-R(2)-4,10-dihydrobenzo[4,5]imidazo[1,2-alpha]pyrimidin-4-ones

Representative benzimidazopyrimidinones were previously reported to be intercalating antitumor agents. In this work, we used 2-substituted 4,10-dihydrobenzo [4,5]imidazo[1,2-alpha]pyrimidin-4-ones for their diversification by regioselective alkylation. Under the conditions established, the alkylation gave 10-alkyl derivatives which permitted the parallel generation of a 500-member library of the title compounds.

Aromatic 2-(thio)ureidocarboxylic acids as a new family of modulators of multidrug resistance-associated protein 1: synthesis, biological evaluation, and structure-activity relationships

Four series of aromatic carboxylic acids were prepared with a urea or thiourea moiety at the neighboring position to the carboxyl group and benzene or thiophene as aromatic scaffold. Using a calcein AM assay, these compounds were evaluated as inhibitors of multidrug resistance-associated protein 1 (MRP1) and selected compounds were examined toward P-glycoprotein (P-gp) as well as breast cancer resistance protein (BCRP) to assess selectivity for MRP1. Two 2-thioureidobenzo[b]thiophene-3-carboxylic acids (48, 49) were identified as particularly potent inhibitors of MRP1, with IC50 values of around 1 microM. The structural features of this new family of nontoxic MRP1 inhibitors include a (thio)urea disubstituted with preferentially two alkyl groups at the terminal nitrogen and an additional fused aromatic ring.

Selectively targeting T- and B-cell lymphomas: a benzothiazole antagonist of alpha4beta1 integrin

Current cancer chemotherapeutic agents clinically deployed today are designed to be indiscriminately cytotoxic, however, achieving selective targeting of cancer malignancies would allow for improved diagnostic and chemotherapeutic tools. Integrin alpha(4)beta(1), a heterodimeric cell surface receptor, is believed to have a low-affinity conformation in resting normal lymphocytes and an activated high-affinity conformation in cancerous cells, specifically T- and B-cell lymphomas. This highly attractive yet poorly understood receptor has been selectively targeted with the bisaryl urea peptidomimetic antagonist 1. However, concerns regarding its preliminary pharmacokinetic (PK) profile provided an impetus to change the pharmacophore from a bisaryl urea to a 2-arylaminobenzothiazole moiety, resulting in an analogue with improved physicochemical properties, solubility, and kidney:tumor ratio while maintaining potency (6; IC(50) = 53 pM). The results presented herein utilized heterocyclic and solid-phase chemistry, cell adhesion assay, and in vivo optical imaging using the cyanine dye Cy5.5 conjugate.

2-Amino- and 2-alkylthio-4H-3,1-benzothiazin-4-ones: synthesis, interconversion and enzyme inhibitory activities

The synthetic access to 2-sec-amino-4H-3,1-benzothiazin-4-ones 2 was explored. Compounds 2 were available from methyl 2-thioureidobenzoates 1, 2-thioureidobenzoic acids 3, and novel 2-thioureidobenzamides 6, respectively, under different conditions. 2-Alkylthio-4H-3,1-benzothiazin-4-ones 5 have been prepared from anthranilic acid following a two step route. Both, benzothiazinones 2 and 5 underwent ring cleavage reactions to produce thioureas 1 and 6, respectively. Twelve benzothiazinones were evaluated as inhibitors against a panel of eight proteases and esterases to identify one selective inhibitor of human cathepsin L, 2b, and one selective inhibitor of human leukocyte elastase, 5i.