Structure-activity relationships of N-benzylsalicylamides for inhibition of photosynthetic electron transport

Inhibition of photosynthetic electron transport (PET) in spinach chloroplasts by sixty-one ring-substituted N-benzylsalicylamides was investigated. The inhibitory potency of the compounds expressed by IC50 value varied from 2.0 to 425.3 μmol/L. Several evaluated compounds can be considered as effective PET inhibitors; these include N-(3,4- dichlorobenzyl)-2-hydroxy-5-nitrobenzamide (IC50 = 2.0 μmol/L), 3,5-dibromo-N-(3,4-dichlorobenzyl)-2-hydroxybenzamide (IC50 = 2.3 μmol/L) and 3,5-dibromo-N-(4-chlorobenzyl)-2-hydroxybenzamide (IC50 = 2.6 μmol/L) with activity comparable with that of the standard Diuron (IC50 = 1.9 μmol/L). The PET inhibiting activity increased approximately linearly with increasing lipophilicity of the compounds as well as with the increasing sum of Hammett σ constants of the substituents on the acyl fragment (R(1) = H, 5-OCH3, 5-CH3, 5-Cl, 5-Br, 5-NO2, 4-OCH3, 4-Cl, 3,5-Cl and 3,5-Br) and the benzylamide fragment (R(2) = H, 4-OCH3, 4-CH3, 4-F, 4-Cl and 3,4-Cl). Based on the evaluated structure-PET inhibiting activity relationships (QSAR) it was confirmed that the inhibitory activity of the compounds depends on lipophilicity (log P or distributive parameters π; (1) and π(2)of individual substituents) and electronic properties of the substituents on the acyl (σ(1)) and the benzylamide fragments (σ(2)), the contribution of σ(1) being more significant than that of σ(2).

[Where does the development of new antituberculotics go? Part 2 - in vitro evaluation]

The present paper is a continuation of a publication of 2012 (Čes. a slov. Farm. 2012; 31, 150-158). It is oriented at the evaluation of potential antituberculotics in vitro, which is the most widely used approach to testing. The paper is based on the information from Chemical Abstracts 2011-2013. It is a selection from nearly three thousand items of information intended to help researchers. The greatest attention is paid to the multiresistant strains of Mycobacterium tuberculosis. In vitro evaluation for the development of new drugs is of great importance, but it is just the first stretch of the road to new medicinal drugs.

Phenyl salicylates - a new group of potential antituberculotics

Antimycobacterial activity of phenyl salicylates (salols) was studied in connection with antituberculotic activity of salicylic derivatives. Phenyl salicylates are esters. Our attention was previously oriented on amides. Phenyl salicylates (salols) represent a new group of antimycobacterial compounds. They are less active than the corresponding amides. The most active compound in the group under study is substituted on phenyl in the salicyl moiety with a 4-methoxy group. The study reports a new item of information about antimycobacterial salicylic derivatives.

[Where does the development of new antituberculotics aim at?]

Several research teams in the Czech and Slovak Republics are oriented on the development of new antitubeculotics. The present article is based mainly on the information from the Chemical Abstracts from the year 2011 and the beginning of the year 2012. It is a selection from almost three thousand reports aiming to help our scientists. The article presents topical information which may be of interest to several pharmaceutical professions.

[Derivatives of phenylcarbamic acid as potential antituberculotics]

Basic esters of phenylcarbamic acid were studied by the teams of Prof. Cizmárik and Prof. Waisser as potential antituberculotics. Their antimycobacterial activity increased with lipophilicity. The most active derivatives were substituted with an alkoxy group in position p- on the phenyl. The activity of some of them almost approached that of INH, but they exceeded it only in the evaluation against the INH-resistant strains M. avium and M. kansasii. The carbamates produced by Prof. Vinsová and co-workers published in the last year show that carbamates can be still topical.

The Oriented Development of Antituberculotics (Part II): Halogenated 3-(4-Alkylphenyl)-1,3-benzoxazine-2,4-(3H)-diones

Based on our previous studies, 21 new halogenated 3-(4-alkylphenyl)-1,3-benzoxazine-2,4-(3H)-diones were synthesized by the reaction of salicylanilides and methyl-chloroformate. All compounds were screened in vitro against three different strains of mycobacterium, and Free-Wilson method was used to establish structure-activity relationships. 6-Bromo-3-(4-butylphenyl)-1,3-benzoxazine-2,4-(3H)-dione 3b proved to be the most active compound of the series.

Hybrid molecules of estrone: New compounds with potential antibacterial, antifungal, and antiproliferative activities

New hybrid molecules of estrone were synthesized as compounds indicating promising biological activity (antibacterial, antimycobacterial, antifungal, and antiproliferative). The prepared molecules contained various heterocyclic units (pyridine, benzylsulfanyl derivatives of pyridine or derivatives of tetrazole) linked to estrone by n-heptyl bridges. The compounds with charge on molecule (the hybrid pyridinium or benzylsulfanylpyridinium salts) exhibited significant biological activity (antibacterial, antimycobacterial, antifungal, and antiproliferative). On the other hand, the compounds not in the form of salts (omega-(1-phenyl-5-tetrazolylthio)heptylethers of estrone) were inactive. The antimycobacterial activities of three different series of tetrazole derivatives (i.e., the hybrid molecules with estrone, tetrazole-5-thiols, and 5-benzylsulfanyl-1-phenyltetrazoles) with the same substituents on phenyl ring were compared. Amongst them, the 5-benzylsulfanyl-1-phenyltetrazoles were the most potent.

QSPR modeling of the half-wave potentials of benzoxazines by optimal descriptors calculated with the SMILES

Optimal descriptors calculated with Simplified Molecular Input Line Entry System (SMILES) notation have been used in quantitative structure-property relationships (QSPR) modeling electrochemical half-wave potential of benzoxazine derivatives by one-variable correlations.

The Oriented Development of Antituberculotics: Salicylanilides

On the basis of our previous results 22 salicylanilides were synthesized. The compounds were tested for in vitro antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium kansasii, and Mycobacterium avium. The Free-Wilson method was used to evaluate structure-antimycobacterial activity relationships. 4-Chloro-N-(4-propylphenyl)salicylamide and 5-chloro-N-(4-propylphenyl)salicylamide were selected for preclinical studies.

QSAR study of antimycobacterial activity of quaternary ammonium salts of piperidinylethyl esters of alkoxysubstituted phenylcarbamic acids

A series of 17 halogenides of quaternary ammonium salts of the alkylpiperidinylethyl esters of 2-pentoxy (and 2-heptoxy) substituted phenylcarbamic acids were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, M. kansasii, and M. avium. Correlation of this action with lipophilicity (log P, 1-octanol-water system) was used for the description of the structure-antimycobacterial activity relationships (QSARs). The activity increased with the increasing lipophilicity of the compounds.

New antimycobacterial 2,3-dihydro-1-alkylindole-2-thiones

A series of 2,3-dihydroindole-2-thiones was evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, M. kansasii, M. fortuitum, two strains of M. intracellulare and three strains of M. avium. 2,3-Dihydro-1-methyl-2-thioxoindole-3-one and 2,3-dihydro-1-butyl-2-thioxoindole-3-one were the most active substances against potentially pathogenic strains, being more active than isoniazide.

New antimycobacterialS-alkylisothiosemicarbazones

In connection with a systematic study of antimycobacterial agents against potentially pathogenic strains the series of 12 S-alkylisothiosemicarbazones was evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, M. kansasii, M. fortuitum, two strains of M. intracellulare and three strains of M. avium. Quinoline-4-carbaldehyde-S-hexyl-isothiohydrazone was found to be more active against potentially pathogenic strains than isoniazide.

A note on the antitubercular activities of 1-aryl-5-benzylsulfanyltetrazoles

A set of 32 1-phenyl-5-benzylsulfanyltetrazoles substituted on the phenyl ring as well as on the benzyl moiety was synthesized. The compounds were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis. The activity against M. tuberculosis becomes higher with increasing electron-accepting properties of the substituents on the phenyl ring. On the other hand, any substitution on the benzylic moiety decreases the activity.

1-Aryl-5-benzylsulfanyltetrazoles, a new group of antimycobacterial compounds against potentially pathogenic strains

A set of 21 1-phenyl-5-benzylsulfanyltetrazoles substituted on the phenyl ring as well as on the benzyl moiety was evaluated for in vitro antimycobacterial activity against Mycobacterium avium and two strains of M. kansasii. We tried to use the Hansch approach, the Free-Wilson approach and their combination for structure-activity correlation but the calculations were statistically insignificant.

Heterocyclic isosters of antimycobacterial salicylanilides

A series of 64 derivatives of substituted heterocyclic analogues of salicylanilides was synthesized. The compounds were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium avium and two strains of Mycobacterium kansasii. For the QSAR study, the combination of Free-Wilson approach with Hansch approach was used. The molecules were separated on the heterocyclic and salicyl moieties and the study of influences of electronic and hydrophobic properties was used as well. The compounds are a new group of potential anti-tuberculotics.

Synthesis and antimycobacterial activity of 1,2,4-triazole 3-benzylsulfanyl derivatives

Series of 3-benzylsulfanyl derivatives of 1,2,4-triazole and 4-methyl-1,2,4-triazole were synthesized by alkylation of starting triazole-3-thiol with appropriately substituted benzyl halide. All members of the set were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, M. avium, and two strains of M. kansasii. The activities were expressed as the minimum inhibitory concentration. The compounds exhibited only a moderate or slight antimycobacterial activity. Minimum inhibitory concentrations fall into a range of 32->1000 micromol/l. The most active substances bear two nitro groups or a thioamide group on the benzyl moiety. As regards the cytotoxicity effect, the evaluated compounds can be considered as moderately toxic.

Synthesis and Antimycobacterial Activity of Pyridylmethylsulfanyl and Naphthylmethylsulfanyl Derivatives of Benzazoles, 1, 2, 4-Triazole, and Pyridine-2-carbothioamide/-2-carbonitrile

A set of four types of benzazoles, 1, 2, 4-triazole, and pyridine-2-carbonitrile/-2-carbothioamide substituted with 1-naphthylmethylsulfanyl or pyridylmethylsulfanyl was prepared to modify the structure of benzylsulfanyl derivatives of the above-mentioned heterocycles. The compounds were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, M. avium, and two strains of M. kansasii. The activities were expressed as the minimum inhibitory concentration (MIC). The MIC values fall into a range of 2 to >1000 micromol/L. Introduction of a pyridyl moiety into the molecule mostly decreased the activity. A naphthyl moiety did not influence the activity in comparison with a phenyl. The most active substances were 4-(3-pyridylmethylsulfanyl)pyridine-2-carbothioamide (7b) (MIC = 2 - >62.5 micromol/L) and 4-(1-naphthylmethylsulfanyl)pyridine-2-carbothioamide (7d) (MIC = 2 - >32 micromol/L).

A new group of potential antituberculotics: hydrochlorides of piperidinylalkyl esters of alkoxy-substituted phenylcarbamic acids

A group of 31 of alkoxy-substituted phenylcarbamic acids with the alkoxy group in ortho, meta or para position, and methyl or ethoxymethyl attached to the ethylene moiety in position 1, including both basic ethyl esters and derivatives branched on ethylene, were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, M. kansasii, and M. avium. To describe the structure-antimycobacterial activity relationships (QSARs), an approach based on a combination of the Free-Wilson analysis was used to express the influence of the substituents on the ethylene group as well as the position of the alkoxy groups on the phenyl ring and of the hydrophobicity of alkyls. In vitro antimycobacterial activity becomes higher with increasing hydrophobic properties of the alkoxy groups. The para- and meta-substituted derivatives were more active than the ortho-substituted ones. Substitution of ethylene in position 1 by methyl increased the activity against M. tuberculosis, a similar substitution by ethoxymethyl increased the activity against M. kansasii. The most active compounds were piperidinyl-1-(ethoxymethyl)ethylesters of heptoxyphenylcarbamic acids.

Antimycobacterial N-pyridinylsalicylamides, isosters of salicylamides

The series of derivatives of substituted N-pyridinylsalicylamides were synthesized. The compounds were evaluated for in vitro antimycobacterial activity against Mycobacterium avium and two strains of Mycobacterium kansasii. In the quantitative structure activity relationships analysis (QSAR), the Free-Wilson and Hansch approaches were used but the analysis was not significant. (The standard deviations of regression coefficients were greater than the values of the coefficients). The molecules were separated the heterocyclic and salicyl moiety in the molecules, and the study of influences of substituents on salicyl moiety was used, as well. 5-chloro-pyridin-2-yl, and the substitution of the salicyl moiety by chlorine in position 4 or 5 had the strongest influence on the increase in antimycobacterial activity.

Similarity approach to QSAR. Application to antimycobacterial benzoxazines

The antimycobacterial activity in six series of substituted 3-phenyl-2H-benzoxazine-2,4(3H)-dithiones and 3-(phenyl)-4-thioxo-2H-benzoxazine-2,4(3H)-diones has been studied using a quantum molecular similarity approach. The approach is based on the use of fragment self-similarity measures as new universal molecular descriptors applicable for the design of novel theoretical QSAR models. Using this approach it was possible to show that while traditional QSAR models were able to describe the activity only within each of the six sets of studied molecules individually, the proposed approach is much more general and a single universal QSAR model describing the activity of all the 39 studied molecules in all the studied series together was built. The replacement of the oxo group by the thioxo group in position 4 on the benzoxazine ring of the antitubercular 3-(phenyl)-2H-benzoxazine-2,4(3H)-diones increases the activity, as well as the similar replacement in position 2.

[Advances in the development of antitubercular agents containing no heterocyclic compounds in the pharmacophore. Part 2. Other derivatives except carboxylic acids]

This paper is the 21st communication in the series of review papers on the development of antituberculotics and the 10th communication summarizing the papers on the development of antituberculotics in recent 15 years. The first seven communications were devoted to heterocyclic compounds, the eighth one to the compounds containing an alkylsulfanyl group in the pharmacophore. The present paper sums up information concerning the compounds not containing a heterocycle in the pharmacophore which are not derivatives of carboxylic acids either. This completes the series of communications recording the development of antituberculotics in the recent period. The communication records papers published since 1980 because it intends to link up with a review paper published in 1982 (Ceskoslov. Farm., 1982; 31, 353-360).

Antimycobacterial activity of piperidinylpropyl esters of alkoxy-substituted phenylcarbamic acids

A series of 17 hydrochlorides of piperidinylpropyl esters of alkoxy-substituted phenylcarbamic acids with the alkoxy group in position 2, 3 or 4 on the phenyl ring, and basic substituents attached to the moiety in position 3, were evaluated for in vitro antimycobacterial activity against the strains of Mycobacterium tuberculosis, M. kansasii and M. avium. To describe the structure-antimycobacterial activity relationships (QSAR), an approach based on the Free-Wilson method was employed to express the differences between individual moieties (including propyl and ethyl). The change of ethyl to propyl moiety increases the activity to M. tuberculosis but decreases the antimycobacterial activity to all potentially pathogenic strains under study.

Influence of Lipophilicity on the Antimycobacterial Activity of the Hydrochlorides of Piperidinylethyl Esters of Ortho-Substituted Phenylcarbamic Acids

A series of 14 hydrochlorides of piperidinylethyl esters of orthosubstituted phenylcarbamic acids were evaluated for in vitro antimycobacterial activity against the strains of Mycobacterium tuberculosis, Mycobactenum kansasii and Mycobactenum avium. In vitro antimycobacterial activrty becomes higher with increasing hydrophobicity of the substituents. The alkoxy group is not necessary in order for the basic ethyl esters of phenylcarbamic acids to display antimycobacterial activity.

Biological activity of 2-hydroxythiobenzanilides and related compounds

Thiobenzanilides substituted in thioacyl moiety with one or more hydroxy groups are interesting for their biological effects depending on the substitution pattern. New findings in mechanisms of action of 2-hydroxybenzanilides insert 2-hydroxybenzanilides and their analogues, e.g. substituted thiobenzanilides, among interesting compounds in the development of new potential antimicrobial drugs. The present review paper with 32 references links up with our previous communications which reviewed biological activity of 2-hydroxybenzanilides and related compounds, and includes the research of mono-, di-, and trihydroxythiobenzanilides carried out in the last period.

[A new group of potential antitubercular agents: antimycobacterial N-benzylsalicylamides]

Linking up with a previous study of antimycobacterial compounds, several groups of N-benzylsalicylamides were prepared and their antimycobacterial activities against the strains Mycobacterium tuberculosis, Mycobacterium kansasii, and Mycobacterium avium were evaluated. The obtained data were analyzed by Free-Wilson method in comparison with their isosteric analogues of 3-hydroxypicolinic and 2-sulfanylbenzoic acids described in the previous communication.

3-Benzyl-2H-1,3-benzoxazine-2,4(3H)-diones, a new group of antimycobacterial compounds against potentially pathogenic strains

A series of derivatives of 3-benzyl-2H-benzoxazine-2,4(3H)-dione substituted in positions 6, 7 or 8 on the benzoxazine, and in positions 3 or 4 on the benzyl moiety was synthesized. The compounds were evaluated for in vitro antimycobacterial activity against Mycobacterium avium and two strains of Mycobacterium kansasii. The disadvantage of the compounds is in their low solubility in water. The antimycobacterial activity of N-benzylsalicylamides correlates with that of 3-benzyl-2H-1,3-benzoxazin-2,4(3H)-diones and depends on the partition coefficients and electronic indexes.

Evaluation of in vitro antifungal activity of N-benzylsalicylamide derivatives

A series of 65 derivatives of N-benzylsalicylamide was tested against eight potentially human pathogenic fungi by microdilution broth method modified according to M27-A standard. The majority of these compounds showed only weak in vitro antifungal activity. The most significant effect was observed against filamentous fungi Trichophyton mentagrophytes, Absidia corymbifera, and Aspergillus fumigatus while yeasts, in general, were less susceptible. N-(4'-Chlorobenzyl) salicylamides, N-(3',4'-dichlorobenzyl)-salicylamides, and partially N-benzylsalicylamides exhibited relatively high in vitro antifungal activity. The most efficient derivatives had MIC < or = 7.8 mumol/L against T. mentagrophytes. Regression analysis suggested an indirect relationship between MIC values and lipophilicity (log P).

Antimycobacterial and antifungal isosters of salicylamides

A set of 40 derivatives of 3-hydroxypicolinic acid and 2-sulfanylbenzoic acid, isosteric to salicylanilides was synthesized. The compounds were evaluated for in vitro activity against Mycobacterium tuberculosis, Mycobacterium kansasii and Mycobacterium avium, Candida albicans, Candida tropicalis, Candida krusei, Candida glabrata, Trichosporon beigelii, Aspergillus fumigatus, Absidia corymbifera, Trichophyton mentagrophytes and Microsporum gypseum. Structure-activity relationships of antimycobacterial activity and antifungal activity against T. mentagrophytes and M. gypseum were analyzed by the Free-Wilson method. An increase in antimycobacterial activity was observed only for the sulfanylbenzoic acid derivatives, especially those with the benzyl moiety. The antifungal activity was not significant.

Antimycobacterial activity of basic ethyl esters of alkoxy-substituted phenylcarbamic acids

A series of 124 basic ethyl esters of alkoxy-substituted phenylcarbamic acids with the alkoxy group in position 2, 3 or 4 on the phenyl ring, and basic substituents attached to the ethyl moiety in position 2, were evaluated for in vitro antimycobacterial activity against strains of Mycobacterium tuberculosis, Mycobacterium kansasii and Mycobacterium avium. In vitro antimycobacterial activity becomes higher with increasing hydrophobic properties of the alkoxy groups. The p- and m-substituted derivatives were more active than the o-substituted ones. Direct relationship between the structure of the basic substituents and the activity was not found.

[Advances in the development of antitubercular agents containing no heterocyclics in the pharmacophore. Part 1. Derivatives of carboxylic acid]

The present paper is the twentieth communication in a series of review papers on the development of antituberculotics and the ninth communication summarizing the work in the development of antituberculotics within recent 15 years. The first seven communications were devoted to heterocyclic compounds, the eighth to substances containing an alkylsulfanyl group in the pharmacophore. The present paper summarizes information about cyrboxylic acids, their amides, anilides, hydrazides, thioamides, thioanilides, thiohydrazides, and amidines. The communication includes papers published after 1980 in order to link up with a review paper devoted to the same topic published in the present series in 1982.

Relationship between the structure and antimycobacterial activity of substituted salicylanilides

A series of 143 salicylanilides substituted in positions 4 and 5 and in positions 3' and 4' was synthesized. The compounds were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium kansasii, and Mycobacterium avium. To describe the structure-antimycobacterial activity relationships (QSARs), an approach based on the combination of the Free-Wilson and Hansch methods was employed (the substituent constants were used in the case of the substituents on the phenyl ring; indicator parameters were used for the substituents on the acyl moiety). The relationships between the antimycobacterial activity and physico-chemical parameters of all substituents were also explored. The quadratic representation of lipophilicity parameters did not lead to significant correlations.

Antimycobacterial 3-aryl-2H-1,3-benzoxazine-2,4(3H)-diones

A series of 153 derivatives of 3-phenyl-2H-benzoxazine-2,4(3H)-dione substituted in position 6 or 7 on benzoxazine and on the phenyl ring was synthesized. The compounds were evaluated in vitro for antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium kansasii and Mycobacterium avium. The activity of the compounds increases with increasing hydrophobicity and electron-withdrawing properties of the substituents on the phenyl ring, whereas the effect of the substituents on the benzoxazine ring seems to be more complex.

On the Relationship between the Structure and Antimycobacterial Activity of Substituted N-Benzylsalicylamides

Sixty-six N-benzylsalicylamides substituted in the acyl moiety in positions 3, 4 or 5 and in position 4 on the benzylic aromatic ring were synthesized. The compounds were tested for in vitro antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium kansasii and Mycobacterium avium. To evaluate structure-antimycobacterial activity relationships (QSARs), approaches based on the Free-Wilson as well as a combination of the Free-Wilson and Hansch methods were employed (substituent constants were used to describe the influence of the benzyl substituents, indicator parameters were used for the substituents on the acyl moiety). The use of the Hammett constants for benzyl substituents was not important for QSAR equations. The quadratic representation of lipophilicity parameters (π2) was significant only in QSAR equations of antimycobacterial activity against M. avium.

[New groups of potential antitubercular agents: 3-(4-ethoxythiocarbonylphenyl)-2-H-benzoxazin-2,4(3H)-diones and 3-(4-ethoxythiocarbonylphenyl)-4-thioxy-2H-benzoxazin-2(3H)-ones]

In connection with the search for new antituberculotics, the present authors prepared a group of derivatives of 3-(4-ethoxythiocarbonylphenyl)-2H-benzoxazin-2,4(3H)-dithione and 3-(4-ethoxythiocarbonylphenyl)-4-thioxy-2H-benzoxazin-2,4(3H)-one. The modifications of substituents were carried out on the benzoxazine ring. The study was based on the present authors' previous assumption that the substitution of the oxo group for the thioxo group was connected with an increase in antimycobacterial activity. The prepared substances were evaluated by the activity against Mycobacterium tuberculosis, Mycobacterium kansasii, and Mycobacterium avium. However, it was concluded that there was no assumed increase in antimycobacterial activity in the groups of 3-(4-ethoxythiocarbonylphenyl)-4-thioxy-2H-benzoxazin-2,4(3H)-one and 3-(4-ethoxythiocarbonylphenyl)-2H-benzoxazin-2,4(3H)-dithione derivatives.