Diltiazem-like calcium entry blockers: a hypothesis of the receptor-binding site based on a comparative molecular field analysis model

Organocatalyzed Enantio- and Diastereoselective Formal Domino 1,3-Dipolar Cycloaddition/Rearrangement: Synthesis of Chiral Pyrrolo-thiazine-2-carbaldehydes

An efficient approach for the synthesis of chiral pyrrolo[1,2-d][1,4]thiazine-2-carbaldehydes is achieved via formal 1,3-dipolar cycloaddition/rearrangement reactions of benzothiazolium salt and α,β-unsaturated aldehydes, utilizing an asymmetric organocatalyst. This process results in the formation of fluorescent, highly enantioenriched chiral molecules with three contiguous stereogenic centers, one of which is a chiral quaternary center, with excellent yields and enantio- and diastereoselectivity. A computational study demonstrated the understanding of the reaction mechanism. The synthetic utility of this protocol was successfully employed for gram scale synthesis. Fluorescent and in silico studies showed the application of the present methodology.

Crystal structure, Hirshfeld surface and crystal void analysis, inter-molecular inter-action energies, DFT calculations and energy frameworks of 2H-benzo[b][1,4]thia-zin-3(4H)-one 1,1-dioxide

In the title mol-ecule, C8H7NO3S, the nitro-gen atom has a planar environment, and the thia-zine ring exhibits a screw-boat conformation. In the crystal, corrugated layers of mol-ecules parallel to the ab plane are formed by N-H⋯O and C-H⋯O hydrogen bonds together with C-H⋯π(ring) and S=O⋯π(ring) inter-actions. The layers are connected by additional C-H⋯O hydrogen bonds and π-stacking inter-actions. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from H⋯O/O⋯H (49.4%), H⋯H (23.0%) and H⋯C/C⋯H (14.1%) inter-actions. The volume of the crystal voids and the percentage of free space were calculated as 75.4 Å3 and 9.3%. Density functional theory (DFT) computations revealed N-H⋯O and C-H⋯O hydrogen-bonding energies of 43.3, 34.7 and 34.4 kJ mol-1, respectively. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via the electrostatic energy contribution. Moreover, the DFT-optimized structure at the B3LYP/ 6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap.

T1143 essential for CaV1.2 inhibition by diltiazem

Careful analysis of previously published reports and some new insights into the structure activity studies revealed an important role of Threonine 1143 in drug binding. Substituting T1143 by alanine and other residues significantly reduced channel inhibition by qDil and Dil. Mutation T1143A did not affect channel activation or inactivation while almost completely diminishing channel block by Dil or qDil. These findings support the view that T1143 serves as drug binding determinant. Other mutations in this position than T1143A (T1143L/Y/S/N/C/V/E) diminished channel inhibition by qDil but additionally affected channel activation and inactivation and may therefore affect channel block allosterically. Collectively, our data suggest that T1143 is an essential diltiazem binding determinant.

3-Aryl-4-nitrobenzothiochromans S,S-dioxide: From Calcium-Channel Modulators Properties to Multidrug-Resistance Reverting Activity

Our research groups have been involved for many years in studies aimed at identifying new active organic compounds endowed with pharmacological properties. In this work, we focused our attention on the evaluation of cardiovascular and molecular drug resistance (MDR) reverting activities of some nitrosubstituted sulphur-containing heterocycles. Firstly, we have examined the effects of 4-nitro-3-(4-methylphenyl)-3,6-dihydro-2H-thiopyran S,S-dioxide 5, and have observed no activity. Then we have extended our investigation to the 3-aryl-4-nitrobenzothiochromans S,S-dioxide 6 and 7, and have observed an interesting biological profile. Cardiovascular activities were assessed for all compounds using ex vivo studies, while the MDR reverting effect was evaluated only for selected compounds using tumor cell lines. All compounds were shown to affect cardiovascular parameters. Compound 7i exerted the most effect on negative inotropic activity, while 6d and 6f could be interesting molecules for the development of more active ABCB1 inhibitors. Both 6 and 7 represent structures of large possible biological interest, providing a scaffold for the identification of new ABCB1 inhibitors.

Phenyliodine(III) Diacetate/I2 -Mediated Domino Approach for Pyrrolo[1,4]Thiazines and 1,4-Thiazines by a One-Pot Morin Rearrangement of N,S-Acetals

An efficient domino transformation using a phenyliodine(III) diacetate (PIDA)/I₂ combination towards Morin 1,4-thiazine compounds has been developed starting from N,S-acetals. The latter leads to "one-step" regioselective methylene insertion without the need for traditional sulfoxide intermediates in good yields. The reaction involves easily accessible N,S-acetals obtained from cost-effective basic ketones and cysteamine as starting materials. This process ultimately leads to 1,4-thiazines related to natural product and fused derivatives necessary for further QSAR study.

Intermolecular sulfenoamination of alkenes with sulfonamides and N-sulfanylsuccinimides to access β-sulfonylamino sulfides and dihydrobenzothiazines

An acid-catalyzed intermolecular sulfenoamination of alkenes is developed with sulfonylamides as the N-source, enabling the synthesis of β-sulfonylamino sulfides and dihydrobenzothiazines.

Comparative molecular field analysis of flavonoid inhibitors of the PIM-1 kinase

The PIM-1 protein, the product of the pim-1 oncogene, is a serine/threonine kinase. Dysregulation of the PIM-1 kinase has been implicated in the development of human malignancies including lymphomas, leukemias, and prostate cancer. Comparative molecular field analysis (CoMFA) is a 3-D QSAR technique that has been widely used, with notable success, to correlate biological activity with the steric and electrostatic properties of ligands. We have used a set of 15 flavonoid inhibitors of the PIM-1 kinase, aligned de novo by common substructure, to generate a CoMFA model for the purpose of elucidating the steric and electrostatic properties involved in flavonoid binding to the PIM-1 kinase. Partial least squares correlation between observed and predicted inhibitor potency (expressed as -logIC50), using a non-cross-validated partial least squares analysis, generated a non-cross-validated q2=0.805 for the training set (n=15) of flavonoids. The CoMFA generated steric map indicated that the PIM-1-binding site was sterically hindered, leading to more efficient binding of planar molecules over (R) or (S) compounds. The electrostatic map identified that positive charges near the flavonoid atom C8 and negative charges near C4' increased flavonoid binding. The CoMFA model accurately predicted the potency of a test set of flavonoids (n=6), generating a correlation between observed and predicted potency of q2=0.825. CoMFA models generated from additional alignment rules, which were guided by co-crystal structure ligand orientations, did not improve the correlative value of the model. Superimposing the PIM-1 kinase crystal structure onto the CoMFA contours validated the steric and electrostatic maps, elucidating the amino acid residues that potentially contribute to the CoMFA fields. Thus we have generated the first predictive model that may be used for the rational design of small-molecule inhibitors of the PIM-1 kinase.

A New Class of Selective Myocardial Calcium Channel Modulators. 2. Role of the Acetal Chain in Oxadiazol-3-one Derivatives

In the framework of the continuing interest of this research group in the use of 8-aryl-8-hydroxy-8H-[1,4]thiazino[3,4-c][1,2,4]oxadiazol-3-ones (1) as calcium entry blockers, a number of acetals were synthesized and assayed "in vitro". All of them are structurally related to diltiazem and pyrrolobenzothiazines. The effect on the biological profile was measured by functional assays for a wide variety of acetal residues: saturated linear and branched chains, short and long unsaturated E and/or Z chains as well as benzyl and methylcyclohexyl residues. From selective assays on the most active derivative (5b) (EC(50) = 0.04 microM), which is 20 times more active than diltiazem (EC(50) = 0.79 microM), a muscarinic or adenosinic mechanism of action was excluded. A 3D QSAR model was obtained and validated with homologous literature data, and a virtual receptor scheme was derived for the unknown binding site. The following pharmacophoric features favorably affect the potency: one positively charged center, three lipophilic groups, and two hydrogen-bonding acceptor groups.

Chalcone dimethylallyltransferase fromMorus nigracell cultures. Substrate specificity studies

A new prenyltransferase (PT) enzyme derived from the microsomal fractions of cell cultures of Morus nigra was shown to be able to prenylate exclusively chalcones with a 2',4'-dihydroxy substitution and the isoflavone genistein. Computational studies were performed to shed some light on the relationship between the structure of the substrate and the enzymatic activity. PT requires divalent cations, particularly Mg(2+), to be effective. The apparent K(m) values for gamma,gamma-dimethylallyldiphosphate and 2',4'-dihydroxychalcone were 63 and 142 microM, respectively. The maximum activity of the enzyme was expressed during the first 10 days of cell growth.

Cardiovascular characterization of [1,4]thiazino[3,4-c][1,2,4]oxadiazol-1-one derivatives: selective myocardial calcium channel modulators

As an extension of previous investigations (Tetrahedron 1999, 55, 5433-5440; J. Heterocycl. Chem. 2000, 37, 875-878), a series of 21 [1,4]thiazino[3,4-c][1,2,4]oxadiazolones, which has already been synthesized (except for compounds 5a, 5b, 6), was evaluated as calcium entry blockers by functional studies, namely, in isolated guinea-pig left and right atria and K(+)-depolarized aortic strips. With the aim of investigating the effect of a condensed benzene ring on the molecular structure and the influence of substituents on the 8-phenyl ring of 4a, ab initio computations (RHF/3-21G) were performed on compounds 3, 4a-d, 4f, and 4k. The results obtained show that many of the compounds studied are potent and selective negative inotropic agents; in particular, compounds 4e and 4f are about 3- and 2-fold more potent than diltiazem, respectively.

Quantitative structure-activity relationships of antianginal drugs

Quantitative structure-activity relationships (QSARs) of various classes of antianginal drugs, e.g. nitrates, beta-adrenergic blocking agents (beta-blockers), and calcium channel blockers (calcium antagonists), have been reviewed. This review gives an overall picture of the mode of action of each class of drugs and points out the specific physicochemical and structural properties that govern their activity. It is observed that in almost all kinds of antianginal drugs the lipophilic factor plays an important role and the next important factor seems to be the steric ones. The electronic factors are found to be occasionally important. In the case of beta-blockers, the most common factor that appeared to govern the activity remained the lipophilicity. In nitrates, too, the activity is observed to primarily depend upon the lipophilicity. In calcium channel blockers, however, the dominant effect is seen to be of steric factors. The steric roles may be essential in drug-receptor interactions, which seem to involve both hydrophobic, and to a lesser extent, electronic interactions.

Synthesis and preliminary biological evaluation of 4,6-disubstituted 3-cyanopyridin-2(1H)-ones, a new class of calcium entry blockers

The preparation of 3-cyano-4,6-diaryl-pyridin-2(1H)-ones 4a-h, calcium entry blockers related to diltiazem, is described starting from 1,3-diaryl-2-propen-1-ones 5. On preliminary pharmacological tests all compounds are active and some of them show calcium antagonistic activity superior or comparable to diltiazem.

Design and synthesis of substituted compounds containing the 1, 4-benzodioxin subunit. New potential calcium antagonists

New compounds possessing 1,4-benzodioxin or its saturated analogous heterocyclic system were synthesized and tested for calcium antagonist activity. Biological differences were seen between the different modifications applied. These compounds have been shown to be representative of a novel series of calcium channel antagonists.

Comparative molecular field analysis of fungal squalene epoxidase inhibitors

Comparative molecular field analysis (CoMFA) of fungal squalene epoxidase inhibitors exhibiting antifungal activity reported in terms of minimum inhibitory concentration (MIC) was performed. Ninety-two molecules belonging to different chemical classes, namely terbinafine analogues, benzylamines, homopropargylamines, and carbon analogues were divided into training set and test set. The initial conformations of the inhibitors obtained from molecular dynamics simulations for 50 ps in aqueous solution were used in the study. Out of three charges used in the study, Gasteiger-H]uckel charges result in models with good internal predictivity. Initial analysis of 92 molecules (analysis A) resulted in models with low predictive r(2) values for activity against three organisms. This data set was modified by exclusion of 13 molecules, and analysis was performed again. This analysis of 79 molecules (analysis B) resulted in improvement in predictivity of the CoMFA models and cross-validated r(2) values of 0.583, 0.509, and 0.502 for Candida albicans, Aspergillus fumigatus, and Trichophyton mentagrophytes, respectively. These models were used to predict the activities of the molecules belonging to the test set. The models from analysis B show better correlative and predictive properties than analysis A. Comparison of CoMFA contour maps for activity against three different fungi revealed differentiating structural requirements.

Cyclic Dipeptides. 3.(1) Synthesis of Methyl (R)-6-[(tert-Butoxycarbonyl)amino]-4,5,6,7- tetrahydro-2-methyl-5-oxo-1,4-thiazepine-3-carboxylate and Its Hexahydro Analogues: Elaboration of a Novel Dual ACE/NEP Inhibitor

Synthetic routes to highly functionalized 1,4-thiazepinones 2 and 3 have been developed. S-Ac-N-Boc-L-Cys-D(L)-ThrOMe 7a,b have been prepared and, after transformation into the corresponding mesylates, used as the cyclization substrates. Treatment of these compounds with LiAlH(OMe)(3) in THF results in mesylate elimination and thiolacetate reduction, giving rise to both a Michael acceptor (alpha,beta-unsaturated ester) and Michael donor (thiol anion), which undergo in situ intramolecular conjugate addition leading to the stereoselective formation of only two of the four possible stereoisomers of 2. On the other hand, PCC/CaCO(3) oxidation of 7a gave in 80% yield the corresponding ketone 11, which was in turn transformed into the enol triflate 15. Cleavage of the thiolacetate moiety, simultaneous elimination of trifluoromethanesulfonic acid to generate an allene system, and addition of the thiol group to the central carbon of the allene to provide the enantiomerically pure cyclic compound 3 in 85% yield was effected via a one-pot reaction by means of MeONa/MeOH. Thiazepinone 3 is an interesting intermediate for the preparation of conformationally restricted dipeptide mimetics, and its elaboration into the dual ACE/NEP inhibitor 4 is reported.

Novel calcium antagonists with both calcium overload inhibition and antioxidant activity. 1. 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-(aminopropyl)thiazolidinones

A series of 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-(aminopropyl)thiazolidinones was synthesized in order to explore novel calcium antagonists with potent antiischemic activity. These compounds were designed to have, in addition to Ca2+ antagonistic activity, both Ca2+ overload prevention and antioxidant activity in one molecule. These three kinds of activity were evaluated by using a K+-depolarized rat aorta, a veratridine-induced Ca2+ overload model of rat cardiomyocytes, and a soybean lipoxygenase-induced lipid peroxidation model of rabbit low-density lipoprotein, respectively. In particular, 2-(3, 5-di-tert-butyl-4-hydroxyphenyl)-3-[3-[N-methyl-N-[2-[3, 4-(methylenedioxy)phenoxy]ethyl]amino]propyl]-1,3-thiazolidin-4-on e (7o) was found to be highly potent and possessed a well-balanced combination of these actions in vitro.

Comparative molecular field analysis (CoMFA) of a series of symmetrical bis-benzamide cyclic urea derivatives as HIV-1 protease inhibitors

A 3D-QSAR study using CoMFA methodology was conducted on a series of 29 symmetrical bis-benzamide cyclic urea derivatives having anti-HIV-1-protease activities. Active site minimization of the ligands was used to exclude conformations which are not sterically accessible within the active site. A significant cross validated correlation coefficient q2 (0.724) was obtained indicating the predictive potential of the model for untested compounds of this class. A significant non-cross-validated correlation coefficient (r2) of 0.971 with a low standard error estimate (S) of 0.119 was obtained indicating that the model reliably predicted the ant-protease activities of poorly to highly active compounds. The model was used to predict the anti-protease activities of eight test-set compounds, and the predicted values were in good agreement with the experimental values. The CoMFA coefficient contour plots identified several key features which explain the wide range of activities. The already reported 2D-QSAR along with the CoMFA model presented here may help in designing effective HIV-1 protease inhibitors.

Synthesis and binding mode of heterocyclic analogues of suramin inhibiting the human basic fibroblast growth factor

The design, synthesis, and biological evaluation of a series of pyrrole and pyrazole congeners 2 of suramin, directed toward the development and identification of new ligands that complex the human fibroblast growth factor (bFGF), thereby inhibiting tumor-promoted angiogenesis, is reported. Compounds 2 were evaluated for their ability to inhibit binding of bFGF to its receptor, in vivo bFGF-induced angiogenesis, and neovascularization of the chorioallantoic membrane in comparison with suramin. These assays showed that ligands 2 exhibit moderate to good activity, comparable to that of suramin, and are less toxic than suramin itself. In this study, affinity data of ligands in combination with the crystal structure of bFGF were used to explain structure-affinity relationships and to gain an insight into the possible mode of ligand-protein interaction. Due to the lack of experimental structural data on the ligand-bFGF complexes, molecular mechanics techniques were used to obtain putative bioactive conformations and to generate docked complexes with the three-dimensional structure of bFGF. These experiments led to suggest that compounds 2 give rise to 1:1 complexes with bFGF through an unprecedented, bidentate attachment of their naphthylsulfonate groups to two main domains, commonly referred to as the heparin binding site and the receptor binding site, on bFGF, thus preventing the interaction of the growth factor with its receptor.