Structural investigation of Ca 2+ antagonists benzofurazanyl and benzofuroxanyl-1,4-dihydropyridines

Quinoxaline 1,4-Dioxides: Advances in Chemistry and Chemotherapeutic Drug Development

N-Oxides of heterocyclic compounds are the focus of medical chemistry due to their diverse biological properties. The high reactivity and tendency to undergo various rearrangements have piqued the interest of synthetic chemists in heterocycles with N-oxide fragments. Quinoxaline 1,4-dioxides are an example of an important class of heterocyclic N-oxides, whose wide range of biological activity determines the prospects of their practical use in the development of drugs of various pharmaceutical groups. Derivatives from this series have found application in the clinic as antibacterial drugs and are used in agriculture. Quinoxaline 1,4-dioxides present a promising class for the development of new drugs targeting bacterial infections, oncological diseases, malaria, trypanosomiasis, leishmaniasis, and amoebiasis. The review considers the most important methods for the synthesis and key directions in the chemical modification of quinoxaline 1,4-dioxide derivatives, analyzes their biological properties, and evaluates the prospects for the practical application of the most interesting compounds.

Revision of the Regioselectivity of the Beirut Reaction of Monosubstituted Benzofuroxans with Benzoylacetonitrile. 6-Substituted quinoxaline-2-carbonitrile 1,4- dioxides: Structural Characterization and Estimation of Anticancer Activity and Hypoxia Selectivity

BACKGROUND

Quinoxaline 1,4-dioxides have a broad range of biological activity that causes a growing interest in their derivatives for drug discovery. Recent studies demonstrated that quinoxaline 1,4- dioxides have a promising anticancer activity and good hypoxia-selectivity.

OBJECTIVE

The preparation, isolation, structure characterization, and screening for anticancer activity of the first representatives of 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides have been described.

MATERIALS AND METHODS

A series of 7- and 6-halogeno-3-phenylquinoxaline-2-carbonitrile 1,4-dioxides was synthesized by the Beirut reaction. The cytotoxicity was assessed by MTT test (72 h incubation) in normoxia (21% O2) and hypoxia (1% O2) conditions.

RESULTS

We found that during the Beirut reaction between a benzofuroxan bearing an electron withdrawing group and benzoylacetonitrile in the presence of triethylamine, in addition to well-known 7-substituted quinoxaline-2-carbonitrile 1,4-dioxides 7-11a, the 6-isomers 7-11b are formed. Moreover, the yield of the 6- isomers increased with the increase in the electron-withdrawing character of the substituent. For benzofuroxans with CO2Me and CF3 groups, 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides 10-11b were the major products. Despite similarities in physicochemical and spectroscopic properties, the obtained isomers exhibit considerable differences in their anticancer activity and hypoxia selectivity.

CONCLUSION

Substituents and their electronic effects play a key role in the formation of 7- and 6-substituted quinoxaline-2-carbonitrile 1,4-dioxides in the Beirut reaction and in the cytotoxicity properties of the obtained isomers.

Synthesis of fused 1,4-dihydropyridines as potential calcium channel blockers

Objective

The aim of this study was to synthesize ten 1,4-dihydropyridine (DHP) derivatives in which substituted cyclohexane rings were fused to the DHP ring and to determine how different ester groups and the benzoyl substituent introduced in 4-phenyl ring affected their calcium channel blocking activity.

Methods

A microwave-assisted one-pot method was applied for the synthesis of compound 1–5 according to a modified Hantzsch reaction. The benzoyl moiety was introduced in the 4-phenyl ring of these dihydropyridines by refluxing with benzoyl chloride in acetone in the presence of anhydrous potassium carbonate. Synthesized products were characterized by elemental analysis, IR, 1H-NMR and 13C-NMR spectroscopy. The inhibitory actions of compounds 1–10 on calcium channel blocking activity were tested on isolated rat aorta preparations.

Results

The obtained pharmacological results showed that although all compounds are potent relaxing agents on isolated rat aorta smooth muscle, introduction of a benzoyloxy substitiuent on the phenyl ring (compound 6–10) decreased the relaxant effect of these compunds.

Conclusion

The reported 1,4-DHP derivatives have calcium channel blocking activity on rat aorta smooth muscle.

15N NMR of 1,4-dihydropyridine derivatives

In this article, we describe the characteristic (15)N and (1)HN NMR chemical shifts and (1)J((15)N-(1)H) coupling constants of various symmetrically and unsymmetrically substituted 1,4-dihydropyridine derivatives. The NMR chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as character and position of the substituent in heterocycle, N-alkyl substitution, nitrogen lone pair delocalization within the conjugated system, and steric effects.

New trypanocidal hybrid compounds from the association of hydrazone moieties and benzofuroxan heterocycle

Hybrid compounds containing hydrazones and benzofuroxan pharmacophores were designed as potential Trypanosoma cruzi-enzyme inhibitors. The majority of the designed compounds was successfully synthesized and biologically evaluated displaying remarkable in vitro activity against different strains of T. cruzi. Unspecific cytotoxicity was evaluated using mouse macrophages, displaying isothiosemicarbazone 10 and thiosemicarbazone 12 selectivity indexes (macrophage/parasite) of 21 and 27, respectively. In addition, the mode of anti-trypanosomal action of the derivatives was investigated. Some of these derivatives were moderate inhibitors of cysteinyl active site enzymes of T. cruzi, cruzipain and trypanothione reductase. ESR experiments using T. cruzi microsomal fraction suggest that the main mechanism of action of the trypanocidal effects is the production of oxidative stress into the parasite.

Second generation of 5-ethenylbenzofuroxan derivatives as inhibitors of Trypanosoma cruzi growth: Synthesis, biological evaluation, and structure–activity relationships

In vitro growth inhibitory activity of 21 new 5-ethenylbenzofuroxan derivatives against the protozoan parasite Trypanosoma cruzi, the causative agent of American trypanosomiasis, was studied. The designed compounds possess the previously described exigencies for optimal anti-parasite activity, the 5-ethenylbenzofuroxanyl moiety with different substituents. The synthetic key for preparing the derivatives was the Wittig procedure, that when 5-formylbenzofuroxan was used as the electrophile the corresponding deoxygenated products were marginally generated. Four of the new derivatives displayed remarkable in vitro activities against the epimastigote form of three strains of T. cruzi, Tulahuen 2, CL Brener, and Y. While the three deoxygenated analogues biologically assayed resulted inactives. Unspecific cytotoxicity was evaluated using human macrophages and active derivatives were not toxic at a concentration at least 13 times that of its IC(50) against T. cruzi (CL Brener strain). From the preliminary structure-activity relationship studies lipophilicity and electronic requirements were found relevant to anti-T. cruzi activity. Active compounds are more lipophilic than inactive ones and it was also identified that an optimum value of R Swain-Lupton's descriptor is required for optimal activity.

New potent 5-substituted benzofuroxans as inhibitors of Trypanosoma cruzi growth: Quantitative structure–activity relationship studies

Benzofuroxan derivatives have been shown to inhibit the growth of Trypanosoma cruzi, the etiological agent of Chagas' disease. Therefore, 2D- and 3D-QSAR models of their in vitro antichagasic activity were developed. Six new derivatives were synthesized to complete a final set of 26 structurally diverse benzofuroxans. The 2D-QSAR model (r = 0.939, r(adj)(2) = 0.849) was generated using multiple regression analysis of tabulated substituents' physicochemical properties and indicator variables. In addition, a 3D-QSAR model (r(2) = 0.997, q(2) = 0.802) was obtained using a comparative molecular field analysis (CoMFA). Due to the well-known benzofuroxan tautomerism, in both approaches (2D- and 3D-QSAR) it was necessary to include an indicator variable to consider the N-oxide position (I(6)). This parameter was established using low-temperature NMR experiments. Both QSAR models identified the electrophilic character of the substituent alpha-atom as a requirement for activity. Further support was found using a density functional theory (DFT) approach.