Synthesis and biological activity of novel 1H,3H-thiazolo[3,4-a]benzimidazoles: non-nucleoside human immunodeficiency virus type 1 reverse transcriptase inhibitors

Novel Kinetic Resolution of Thiazolo-Benzimidazolines Using MAO Enzymes

The kinetic resolution of racemic 1H,3H-thiazolo[3,4-a]benzimidazoline (TBIM) heterocycles was achieved using E. coli whole cells expressing the MAO-N D11 enzyme. Several cosolvents were screened using TBIM 2a as the substrate. DMF was the best cosolvent, affording the pure enantiomer (+)-2a in 44% yield, 94% ee. The stereochemistry of TBIM was predicted by means of ab initio calculations of optical rotation and circular dichroism spectra. The reaction scope was investigated for 11 substituted (±) TBIM using an optimized protocol. The best yield and % ee were obtained for the nonsubstituted 2a. Among the substituted compounds, the 5-substituted-TBIM showed better % ee than the 4-substituted one. The small electron donor group (Me) led to better % ee than the electron-withdrawing groups (-NO2 and -CO2Et), and the bulky naphthyl group was detrimental for the kinetic resolution. Docking experiments and molecular dynamics (MD) simulations were employed to further understand the interactions between MAO-N D11 and the thiazolo-benzimidazoline substrates. For 2a, the MD showed favorable positioning and binding energy for both enantiomers, thus suggesting that this kinetic resolution is influenced not only by the active site but also by the entry tunnel. This work constitutes the first report of the enzymatic kinetic resolution applied to TBIM heterocycles.

Photocatalyst-free visible-light triggered amination of benzo[c][1,2,5]thiadiazole: direct C-N bond formation from C(sp2)-H bond

The photoredox amination of arene protocols mostly comprises photocatalyst-mediated transformations. Herein, we presented the photocatalyst-free, visible-light promoted, direct conversion of C(sp²)-H to C(sp²)-N method. Multipurpose benzothiadiazoles are used as model synthons and secondary amines as aminating agents. Mechanistic study reveals that the radical reaction mechanism proceeds through nitrogen-centered radical generation, followed by the addition of arenes, which was demonstrated for the present amination protocol of benzothiadiazole with secondary amines in an atom economical fashion.

Visible-light-mediated one-pot efficient synthesis of 1-aryl-1H,3H-thiazolo[3,4-a]benzimidazoles: a metal-free photochemical approach in aqueous ethanol

A new metal-free approach to construct medicinally valuable 1-aryl-1H,3H-thiazolo[3,4-a]benzimidazoles under visible light irradiation in aqueous ethanol medium at room temperature has been developed. The present process was performed with 1,2-phenylenediamines, aromatic aldehydes and 2-mercaptoacetic acid utilizing a simple household 22 W compact fluorescent lamp to generate C-S, C-N bonds through radical intermediates. This visible-light-promoted synthesis provides lower cost, operation simplicity and high functional groups tolerating ability with short reaction time and high yield under mild reaction conditions.

Mol-ecular and crystal structure, Hirshfeld analysis and DFT investigation of 5-(furan-2-yl-methyl-idene)thia-zolo[3,4-a]benzimidazole-2-thione

The thia-zolo[3,4-a]benzimidazole fused-ring system in the title compound, C14H8N2OS2, is nearly planar, the r.m.s. deviation being 0.0073 Å. The thia-zolo-benzimidazole-2-thione system is almost in the same plane as the furan-2-yl-methyl-ene moiety, with a dihedral angle of 5.6 (2)° between the two least-squares planes. In the crystal, adjacent mol-ecules are connected by weak inter-molecular inter-actions (C-H⋯N and slipped π-π stacking) into a three-dimensional network. The nature of the inter-molecular inter-actions was also qu-anti-fied by Hirshfeld surface analysis. DFT analysis indicates a good agreement of the experimentally determined and the theoretically calculated mol-ecular structures.

Synthesis, Antibacterial, and Anti HepG2 Cell Line Human Hepatocyte Carcinoma Activity of Some New Potentially Benzimidazole-5-(Aryldiazenyl)Thiazole Derivatives

The paper describes the synthesis and biological evaluation of some new benzimidazole derivatives as potent clinical drugs that are useful in the treatment of some microbial infections and tumor inhibition. The starting compound 2-(bromomethyl)-1H-benzimidazole (1) was prepared, and hence underwent interesting functionalization reactions to afford several series of benzimidazole-5-(aryldiazenyl)thiazole derivatives: 3a⁻c, 7a⁻c, and 8a⁻c. The antibacterial activities of the synthesized compounds were evaluated by calculation of the inhibition zone diameter (mm) and the determination of minimum inhibitory concentration (µg/mL) against selected pathogenic bacteria Staphylococcus aureus (Gram-positive bacteria) and Escherichia coli (Gram-negative bacteria).Noticeable efficiency was found based on in vitro screening for their antioxidant activity and cytotoxicity effect against the human liver cancer cell line (HepG2) and human hepatocyte carcinoma cells at relatively high concentrations.

Ball Milling Assisted Solvent and Catalyst Free Synthesis of Benzimidazoles and Their Derivatives

Benzoic acid and o-phenylenediamine efficiently reacted under the green solvent-free Ball Milling method. Several reaction parameters were investigated such as rotation frequency; milling balls weight and milling time. The optimum reaction condition was milling with 56.6 g weight of balls at 20 Hz frequency for one hour milling time. The study was extended for synthesis of a series of benzimidazol-2-one or benzimidazol-2-thione using different aldehydes; carboxylic acids; urea; thiourea or ammonium thiocyanate with o-phenylenediamine. Moreover; the alkylation of benzimidazolone or benzimidazolthione using ethyl chloroacetate was also studied.

Regioselective Synthesis of Some Pyrazole Scaffolds Attached to Benzothiazole and Benzimidazole Moieties

Condensation of 2-(benzothiazol-2-yl)acetonitrile (1) or 2-(1-methyl-1H-benzimidazol-2-yl)acetonitrile (2) with thiophene-2-carbaldehyde afforded the corresponding acrylonitrile derivatives3or4, respectively. The 1,3-dipolar cycloaddition reaction of the acrylonitrile3or4with nitrile-imine6gave novel pyrazole derivatives pendant to benzothiazole and benzimidazole. The pyrazoline derivative7was converted into the corresponding pyrazole derivative11via thermal elimination of hydrogen cyanide upon heating in sodium ethoxide solution. The structures of the synthesized products were confirmed by IR,1H NMR, and mass spectral techniques.

Yet another ten stories on antiviral drug discovery (part D): paradigms, paradoxes, and paraductions

This review article presents the fourth part (part D) in the series of stories on antiviral drug discovery. The stories told in part D focus on: (i) the cyclotriazadisulfonamide compounds; (ii) the {5-[(4-bromophenylmethyl]-2-phenyl-5H-imidazo[4,5-c]pyridine} compounds; (iii) (1H,3H-thiazolo[3,4-a]benzimidazole) derivatives; (iv) T-705 (6-fluoro-3-hydroxy-2-pyrazinecarboxamide) and (v) its structurally closely related analogue pyrazine 2-carboxamide (pyrazinamide); (vi) new strategies for the treatment of hemorrhagic fever virus infections, including, as the most imminent, (vii) dengue fever, (viii) the veterinary use of acyclic nucleoside phosphonates; (ix) the potential (off-label) use of cidofovir in the treatment of papillomatosis, particularly RRP (recurrent respiratory papillomatosis); and (x) finally, the prophylactic use of tenofovir to prevent HIV infections.

The thiazolobenzimidazole TBZE-029 inhibits enterovirus replication by targeting a short region immediately downstream from motif C in the nonstructural protein 2C

TBZE-029 {1-(2,6-difluorophenyl)-6-trifluoromethyl-1H,3H-thiazolo[3,4-a]benzimidazole} is a novel selective inhibitor of the replication of several enteroviruses. We show that TBZE-029 exerts its antiviral activity through inhibition of viral RNA replication, without affecting polyprotein processing. To identify the viral target of TBZE-029, drug-resistant coxsackievirus B3 (CVB3) was selected. Genotyping of resistant clones led to the identification of three amino acid mutations in nonstructural protein 2C, clustered at amino acid positions 224, 227, and 229, immediately downstream of NTPase/helicase motif C. The mutations were reintroduced, either alone or combined, into an infectious full-length CVB3 clone. In particular the mutations at positions 227 and 229 proved essential for the altered sensitivity of CVB3 to TBZE-029. Resistant virus exhibited cross-resistance to the earlier-reported antienterovirus agents targeting 2C, namely, guanidine hydrochloride, HBB [2-(alpha-hydroxybenzyl)-benzimidazole], and MRL-1237 {1-(4-fluorophenyl)-2-[(4-imino-1,4-dihydropyridin-1-yl)methyl]benzimidazole hydrochloride}. The ATPase activity of 2C, however, remained unaltered in the presence of TBZE-029.

Anti-enterovirus activity and structure–activity relationship of a series of 2,6-dihalophenyl-substituted 1H,3H-thiazolo[3,4-a]benzimidazoles

Despite the fact that enteroviruses are implicated in a variety of human diseases, there is no approved therapy for the treatment of enteroviral infections. Here, a series of 2,6-dihalophenyl-substituted 1H,3H-thiazolo[3,4-a]benzimidazoles with anti-enterovirus activity is reported. The compounds elicit potent activity against coxsackievirus A9, echovirus 9 and 11 and all six strains of coxsackievirus B. A structure-activity relationship analysis revealed that the presence of substituents at position 6 of the tricyclic system positively influences the antiviral activity, whereas substitutions at position 7 are less favorable. In particular a 6-trifluoromethyl substitution leads to a substantial improvement of the antiviral activity as compared to the unsubstituted structure. Furthermore, an additional introduction of a 2-Cl, 6-F substitution on the phenyl at C-1 results in a further increase of the antiviral activity. Hence, 1-(2-chloro-6-fluorophenyl)-6-trifluoromethyl-1H,3H-thiazolo[3,4-a]benzimidazole results in a dose-dependent inhibition of viral replication with a 50% effective concentration (EC50) of 0.41 microg/ml without any detectable cytotoxicity at the highest concentration (100 microg/ml) tested.

Antihelminthic activity of some newly synthesized 5(6)-(un)substituted-1H-benzimidazol-2-ylthioacetylpiperazine derivatives

Piperazine derivatives of 5(6)-substituted-(1H-benzimidazol-2-ylthio)acetic acids were synthesized by using two methods and studied for antihelminthic activity. The antiparasitic screening showed that compounds 18-24 exhibited higher activity against Trichinella spiralis in vitro in comparison to methyl 5-(propylthio)-1H-benzimidazol-2-yl-carbamate (albendazole). Most active were compounds 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-1H-benzimidazole 21 and 2-{[2-oxo-2-(4-benzhydrylpiperazin-1-yl)ethyl]thio}-5(6)-methyl-1(H)-benzimidazole 19 as well as 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-5(6)-methyl-1(H)-benzimidazole 23 with efficacy of 96.0%, 98.4% and 100%, respectively. The tested derivatives 15-19 and 20-23 were less active against Syphacia obvelata in vivo than albendazole and exhibited the same efficacy as piperazine, but in twice lower concentration.Compounds 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-1H-benzimidazole 21, 1,4-bis[(5(6)-methyl-1(H)-benzimidazol-2-ylthio)acetyl]piperazine 17 and 2-({2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}thio)-5(6)-methyl-1(H)-benzimidazole 23 had higher efficacies of 73%, 76%, and 77%, respectively.

Multiple tandem mass spectrometry-based investigation of the behaviour of some thiazol-benzimidazolones and 2-benzimidazolylsulfanyl ethanones

The behaviour in electrospray conditions of a series of thiazol-benzimidazolones and 2- benzimidazolylsulphanyl ethanones has been studied by means of multiple tandem mass spectrometry experiments. Even though the experimental conditions were the same, different behaviour is observed for the two classes of compounds. In the case of thiazol-benzimidazolones, the formation of a protonated complex with CH3OH employed as solvent is observed, but in the case of 2-benzimidazolylsulphanyl ethanones the formation of MNa+ ions is privileged. This behaviour has been related to molecular structure. The collisionally-induced decompositions of MH+ ions have been rationalised in terms of the Stevenson-Audier and even-electron rules, as well as on the basis of proton affinity data. Thus, protonated thiazol-benzimidazolones undergo facile loss of CO and a series of different decomposition pathways involving cleavage of the thiazolone ring that reflect the structure of the neutral fragments. In contrast, the decompositions of the protonated 2-benzimidazolylsulphanyl ethanones are mainly related to the piperazine moiety, suggesting that the protonation takes place on this substructural unit.

Highly Active Antiretroviral Therapy and Viral Response in HIV Type 2 Infection

Human immunodeficiency virus type 2 (HIV-2), the second human retrovirus known to cause AIDS, is endemic to West Africa but is infrequently found outside this region. We present a case series of 10 HIV-2--infected individuals treated in the United States. Physicians applied the principles of highly active antiretroviral therapy (HAART), normally used in treating HIV type 1, with modifications considered appropriate for treating HIV-2. CD4+ cell count, HIV-2 virus load, and clinical status were found to correlate well, providing evidence that HIV-2 virus load is useful in managing treatment of patients with HIV-2 who are receiving therapy. However, HAART regimens with predicted efficacy for treatment of HIV type 1 infection are not as efficacious for treatment of HIV-2. Controlled clinical trials of HIV-2-infected patients receiving various HAART regimens are needed to provide therapeutic guidance to the medical community.

Synthesis of new 2,3-diaryl-1,3-thiazolidin-4-ones as anti-HIV agents

Several 2,3-diaryl-1,3-thiazolidin-4-ones were synthesized and evaluated as anti-HIV agents. The results of the in vitro tests showed that some of them were highly effective inhibitors of HIV-1 replication at 30-50 nM concentrations with minimal cytotoxicity, thereby acting as non-nucleoside HIV-1 reverse transcriptase inhibitors (NNRTIs).

Anti-HIV agents: design and discovery of new potent RT inhibitors

This paper reports our work in the field of nonnucleoside RT inhibitors (NNRTIs). On the basis of extensive studies on 1H,3H-thiazolo[3,4-a]benzimidazole derivatives (TBZs) followed by structure-activity relationship (SAR) considerations and molecular modeling, the design and synthesis of a series of 2,3-diaryl-1,3-thiazolidin-4-ones have been performed. Some derivatives proved to be highly effective in inhibiting human immunodeficiency virus type-1 (HIV-1) replication at nanomolar concentrations with minimal toxicity, acting as reverse transcriptase (RT) inhibitors. Computational studies were used in order to probe the binding of our ligands to HIV-1-RT.

Synthesis and anti-HIV activity of 2,3-diaryl-1,3-thiazolidin-4-ones

Several 1,3-thiazolidin-4-ones bearing a 2,6-dihalophenyl group at C-2 and a variously substituted phenyl ring at N-3 have been synthesized and tested as anti-HIV agents. The results of the in vitro tests showed that some of them proved to be effective inhibitors of HIV-1 replication.

Synthesis and anti-hIV activity of 1-(2,6-difluorophenyl)-1H,3H-thiazolo[3,4-a]benzimidazole structurally-related 1,2-substituted benzimidazoles

The synthesis of 1,2-substituted benzimidazoles is reported. These novel derivatives share chemical similarities with 1-aryl-1H,3H-thiazolo[3,4-a]benzimidazoles, a class of HIV-1 NNRTIs studied widely. All compounds prepared were tested in MT-4 cells to explore their potential anti-HIV activity and were found to be less potent than 1-(2,6-difluorophenyl)-1H,3H-thiazolo[3,4-a]benzimidazole (TBZ).

Synthesis and anti-HIV activity of 2,3-diaryl-1,3-thiazolidin-4-(thi)one derivatives

Several 2,3-diaryl-1,3-thiazolidine-4-thione derivatives and 2,3-diaryl-1,3-thiazolidin-4-ones bearing a methyl group at C-5 position have been synthesized and tested as anti-HIV agents. The results of the in vitro tests showed that some of them proved to be effective inhibitors of HIV-1 replication.

Discovery of 2,3-diaryl-1,3-thiazolidin-4-ones as potent anti-HIV-1 agents

Design, synthesis and anti-HIV activity of a series of 2,3-diaryl-1,3-thiazolidin-4-ones are reported. Some derivatives proved to be highly effective in inhibiting HIV-1 replication at nanomolar concentrations thereby acting as non-nucleoside HIV-1 RT inhibitors (NNRTIs). SAR studies evidenced that the nature of the substituents at the 2 and 3 positions of the thiazolidinone nucleus largely influenced the in vitro anti-HIV activity of this new class of potent antiviral agents.

Synthesis, biological activity, pharmacokinetic properties and molecular modelling studies of novel 1H,3H-oxazolo[3,4-a]benzimidazoles: non-nucleoside HIV-1 reverse transcriptase inhibitors

New 1H,3H-oxazolo[3,4-albenzimidazoles (OBZs) were synthesized as HIV-1 non-nucleoside reverse transcriptase inhibitors (NNRTI) to extend the structure-activity relationships observed for an early series of related 1H,3H-thiazolo[3,4-a]benzimidazole derivatives (TBZs). The new compounds showed inhibitory activity against the replication of various HIV-1 strains, including NNRTI-resistant strains. Testing of a representative OBZ derivative in an HPLC assay on biological fluids, indicated that the sulphur substitution appreciably improved the metabolic stability of the TBZ compound. In addition, molecular modelling studies demonstrated that OBZs, TBZs and other NNRTIs have similar structural properties, that is a butterfly-like conformation, which is a key structural requirement for reverse transcriptase inhibition.

Novel compounds in preclinical/early clinical development for the treatment of HIV infections

Virtually all the compounds that are currently used, or under advanced clinical trial, for the treatment of HIV infections, belong to one of the following classes: (i) nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), (ii) non-nucleoside reverse transcriptase inhibitors (NNRTIs) and (iii) protease inhibitors (PIs). In addition to the reverse transcriptase and protease step, various other events in the HIV replicative cycle are potential targets for chemotherapeutic intervention: (i) viral adsorption, through binding to the viral envelope glycoprotein gp120 (polysulphates, polysulphonates, polyoxometalates, zintevir, negatively charged albumins); (ii) viral entry, through blockade of the viral coreceptors CXCR4 and CCR5 [bicyclams (AMD3100), polyphemusins (T22), TAK-779]; (iii) virus-cell fusion, through binding to the viral glycoprotein gp41 [T-20 (DP-178), siamycins, betulinic acid derivatives]; (iv) viral assembly and disassembly, through NCp7 zinc finger-targeted agents [2,2'-dithiobisbenzamides (DIBAs), azadicarbonamide (ADA)]; (v) proviral DNA integration, through integrase inhibitors such as L-chicoric acid; (vi) viral mRNA transcription, through inhibitors of the transcription (transactivation) process (peptoid CGP64222, fluoroquinolone K-12, Streptomyces product EM2487). Also, in recent years new NRTIs, NNRTIs and PIs have been developed that possess, respectively, improved metabolic characteristics (i.e. phosphoramidate and cyclosaligenyl pronucleotides of d4T), or increased activity against NNRTI-resistant HIV strains, or, in the case of PIs, a different, non-peptidic scaffold. Given the multitude of molecular targets with which anti-HIV agents can interact, one should be cautious in extrapolating from cell-free enzymatic assays to the mode of action of these agents in intact cells. A number of compounds (i.e. zintevir and L-chicoric acid, on the one hand; and CGP64222 on the other hand) have recently been found to interact with virus-cell binding and viral entry in contrast to their proposed modes of action targeted at the integrase and transactivation process, respectively.