Highly Potent, Water Soluble Benzimidazole Antagonist for Activated α4β1 Integrin

N-substitution Reactions of 2-Aminobenzimidazoles to Access Pharmacophores

Benzimidazole (BI) and its derivatives are interesting molecules in medicinal chemistry because several of these compounds have a diversity of biological activities and some of them are even used in clinical applications. In view of the importance of these compounds, synthetic chemists are still interested in finding new procedures for the synthesis of these classes of compounds. Astemizole (antihistaminic), Omeprazole (antiulcerative), and Rabendazole (fungicide) are important examples of compounds used in medicinal chemistry containing BI nuclei. It is interesting to observe that several of these compounds contain 2-aminobenzimidazole (2ABI) as the base nucleus. The structures of 2ABI derivatives are interesting because they have a planar delocalized structure with a cyclic guanidine group, which have three nitrogen atoms with free lone pairs and labile hydrogen atoms. The 10-π electron system of the aromatic BI ring conjugated with the nitrogen lone pair of the hexocyclic amino group, making these heterocycles to have an amphoteric character. Synthetic chemists have used 2ABI as a building block to produce BI derivatives as medicinally important molecules. In view of the importance of the BIs, and because no review was found in the literature about this topic, we reviewed and summarized the procedures related to the recent methodologies used in the N-substitution reactions of 2ABIs by using aliphatic and aromatic halogenides, dihalogenides, acid chlorides, alkylsulfonic chlorides, carboxylic acids, esters, ethyl chloroformates, anhydrides, SMe-isothioureas, alcohols, alkyl cyanates, thiocyanates, carbon disulfide and aldehydes or ketones to form Schiff bases. The use of diazotized 2ABI as intermediate to obtain 2-diazoBIs was included to produce Nsubstituted 2ABIs of pharmacological interest. Some commentaries about their biological activity were included.

De novo design and synthesis of dipyridopurinone derivatives as visible-light photocatalysts in productive guanylation reactions

Described here is the de novo design and synthesis of a series of 6H-dipyrido[1,2-e:2',1'-i]purin-6-ones (DPs) as a new class of visible-light photoredox catalysts (PCs). The synthesized DP1-5 showed their λ _Abs(max) values in 433-477 nm, excited state redox potentials in 1.15-0.69 eV and -1.41 to -1.77 eV (vs. SCE), respectively. As a representative, DP4 enables the productive guanylation of various amines, including 1°, 2°, and 3°-alkyl primary amines, secondary amines, aryl and heteroaryl amines, amino-nitrile, amino acids and peptides as well as propynylamines and α-amino esters giving diversities in biologically important guanidines and cyclic guanidines. The photocatalytic efficacy of DP4 in the guanylation overmatched commonly used Ir and Ru polypyridyl complexes, and some organic PCs. Other salient merits of this method include broad substrate scope and functional group tolerance, gram-scale synthesis, and versatile late-stage derivatizations that led to a derivative 81 exhibiting 60-fold better anticancer activity against Ramos cells with the IC₅₀ of 0.086 μM than that of clinical drug ibrutinib (5.1 μM).

Palladium-Catalyzed Ligand-Free C-N Coupling Reactions: Selective Diheteroarylation of Amines with 2-Halobenzimidazoles

2-Aminobenzimidazoles are widely present in a number of bioactive molecules. Generally, the preparation of these molecules could be realized by the mono-substitution of 2-halobenzimidazoles with amines. However, rare examples were reported for the di-substituted products and the selectivity of mono- vs. di-substitution was relatively low. Considering the potential values of the di-substituted products, we accomplished the first selective diheteroarylation of amines with 2-halobenzimidazoles. Notably, this Pd-catalyzed transformation was realized under ligand-free conditions. Accordingly, numerous target products were efficiently produced from various aromatic or aliphatic amines and 2-halobenzimidazoles. It was worth noting that two representative products were further confirmed by X-ray crystallography. More significantly, this catalytic process could be applied to the synthesis and discovery of new bioactive compounds, which demonstrated the synthetic usefulness of this newly developed approach.

Nickel-catalyzed Chan–Lam cross-coupling: chemoselective N-arylation of 2-aminobenzimidazoles

A complementary set of Ni- and Cu-based catalyst systems for the chemoselective N-arylation of 2-aminobenzimidazoles have been developed.

Synthesis of new α-aminophosphonate derivatives incorporating benzimidazole, theophylline and adenine nucleobases using l-cysteine functionalized magnetic nanoparticles (LCMNP) as magnetic reusable catalyst: evaluation of their anticancer properties

A new class of α-aminophosphonate derivatives incorporating benzimidazole, theophylline and adenine nucleobases were synthesized in a three-step process and the anticancer activities of selected ligands were evaluated.

Convenient Two-step One-pot Synthesis of Benzimidazoles Using 2-nitroanilines and Thiourea Dioxide

A new convenient method for the conversion of 2-nitroanilines into benzimidazoles by two-step one-pot procedure is reported. The procedure involves the reduction of nitro group followed by the intramolecular cyclisation of the corresponding o-phenylenediamines utilising thiourea dioxide and sodium hydroxide at 70 °C in mixed solvents of H2O and EtOH (v/v, 3/1). The yields are good to excellent and the workup is simple.

Copper-catalyzed sequential N-arylation of C-amino-NH-azoles

Copper(ii)-catalyzed boronic acid promoted C–N bond cross-coupling reactions have been developed for sequential N-arylation of C-amino-NH-azoles.

2-Phenylamino-6-cyano-1H-benzimidazole-based isoform selective casein kinase 1 gamma (CK1γ) inhibitors

Screening of the Amgen compound library led to the identification of 2-phenylamino-6-cyano-1H-benzimidazole 1a as a potent CK1 gamma inhibitor with excellent kinase selectivity and unprecedented CK1 isoform selectivity. Further structure-based optimization of this series resulted in the discovery of 1h which possessed good enzymatic and cellular potency, excellent CK1 isoform and kinase selectivity, and acceptable pharmacokinetic properties.

Canine malignant melanoma alpha-3 integrin binding peptides

There is a need to develop novel targeted imaging and therapeutic agents that can aid in early diagnosis, detection of metastasis and treatment of melanoma. Alpha-3 integrin is overexpressed in 82% of metastatic melanomas in humans and may be a potential target for peptide ligands carrying therapeutic agents. Five melanoma cell lines were generated from canine primary oral and metastatic canine tumors, grown in mice, and validated with melanoma markers Melan A, S-100, Micropthalmia transcription factor (MITF), Tyrosinase, and MART-1. The melanoma cell lines were tested for binding affinity to previously published alpha-3 integrin-binding peptides containing the cdGXGXXc motif. Fluorescent conjugates of the alpha-3 integrin binding OA02 peptide were used to quantify receptor affinity in the cell lines, a specimen of canine primary oral melanoma, and melanoma xenografts. Alpha-3 integrin was expressed by all 5 canine melanoma cell lines. Four of the 5 lines as well as the primary canine tumor showed affinity to alpha-3 integrin binding peptides with the cdGXGXXc motif. Optical imaging of canine melanoma xenografts in nude mice indicates rapid, strong uptake of the optical tracer in the tumor with an average persistence of approximately 48 h. Ex vivo images showed high tumor-to-background ratio, with tumor signals more than twice that of the kidney and other vital organs. We propose that integrin alpha-3 integrin binding ligands could potentially become useful probes for imaging and delivery of cytotoxic agents for the treatment of melanoma.

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.

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.

Application of a trifunctional reactive linker for the construction of antibody-drug hybrid conjugates

A flexible, trifunctional poly(ethylene glycol)-succinamide-Lysine-Lysine-maleimide (PEG-SU-Lys-Lys-mal) linker was employed to simultaneously allow biotin tagging and cell-surface targeting through an integrin alpha(4)beta(1)-binding peptidomimetic that was regiospecifically conjugated to an IgG1-derived Fc fragment with an engineered C-terminal selenocysteine residue. The resulting antibody derivative mediates Fc receptor binding by virtue of the Fc protein and selectively targets cancer cells expressing human integrin alpha(4)beta(1). The PEG-SU-Lys-Lys-mal linker may have general utility as an organic tether for the construction of antibody-drug conjugates.