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

Hybrids of salicylalkylamides and Mannich bases: control of the amide conformation by hydrogen bonding in solution and in the solid state

3-Aminomethylation of salicylalkylamides afforded hybrids with a Mannich base. In addition, it triggered the rotation of the amide bond. The observed conformational switch is driven by strong intramolecular hydrogen bonding between the Mannich base and phenolic group. Crystal structure analysis reveals the stabilization of the hybrid molecules by double hydrogen bonding of the phenolic OH, which acts as an acceptor and donor simultaneously. The molecules contain an amide site and a Mannich base site in an orthogonal spatial arrangement. The intramolecular hydrogen bonds are persistent in a nonpolar solvent (e.g., chloroform). The conformational change can be reversed upon protection or protonation of the Mannich base nitrogen.

The synthesis and characterization of some novel 5-chloro-2-(substituted alkoxy)-N-phenylbenzamide derivatives

To obtain biologically active compounds, the synthesis of some new derivatives with an o-hydroxybenzamide structure was performed. The ethyl esters 4-6 were obtained by the reaction of 5-chloro-2-hydroxy-N-phenylbenzamide and chloro-substituted acid ethyl esters 1-3 in ethyl methyl ketone. The obtained ethyl esters were condensed with hydrazine yielding the hydrazides 7-8. The hydrazones 11-14 were obtained by the reaction of the hydrazides and the chloro-substituted benzaldehydes 9-10. All the newly synthesized compounds were characterized by FTIR, 1H-NMR, 13C-NMR, MS and elemental analyses.

The synthesis and characterization of some ortho-substituted phenoxyalkanoic acids and their derivatives

The synthesis of 2-phenoxyalkanoic acids (ethanoic, propanoic, butanoic) was realized by the reaction of ortho-hydroxybenzamide respectively N-phenyl-o-hydroxybenzamide with ?-halogenated acids in aqueous sodium hydroxide solution. 2-[o-(carbamoyl)phenoxy]-2-methyl- and 2-[o-(phenylcarbamoyl)phenoxy]-2-methyl- propanoic acids were obtained by reaction of the appropriate amide with acetone, chloroform and sodium hydroxide. Ethyl esters of 2-phenoxyalkanoic acids were obtained by the reaction of the amide with ethyl esters of ?-halogenated acids in different reaction media. Starting from the ethyl esters of 2-[2-(N-phenylcarbamoyl) phenoxy]alkanoic acids with hydrazine 2-[2-(N-phenylcarbamoyl)phenoxy]alkanoic acids hydrazides were obtained, which are considered key intermediates for the synthesis of several series of new compounds. Schiff bases and N-imido-derivatives were obtained by condensation of hydrazide with substituted aromatic aldehydes respectively maleic anhydride. The synthesized compounds were characterized by physico-chemical methods (FTIR, NMR and mass spectrometry). .

Synthesis and Biological Evaluation of (E)-3-(Nitrophenyl)-1-(pyrazin-2-yl)prop-2-en-1-ones

The title (E)-(3-nitrophenyl)-1-(pyrazin-2-yl)prop-2-en-1-ones were prepared by the Claisen- Schmidt condensation of acetylpyrazines and 2-nitro-, 3-nitro- and 4-nitrobenzaldehyde in pyridine using diethylamine as the catalyst. The compounds were bioassayed for in vitro antifungal, antimycobacterial and photosynthesis-inhibiting activity. The high potency of (E)-1-(5-tert-butylpyrazin-2-yl)-3-(4-nitrophenyl)prop-2-en-1-one againstMycobacterium tuberculosis(MIC 0.78 μg/ml) and moderate activities of several compounds againstTrichophyton mentagrophytesandCandidaspp. do not support the assumption that phenolic groups are essential for antimycobacterial and antifungal activity of chalcones and their analogues. In fact, the nitro-substituted compounds were superior to the previously described hydroxylated congeners with antimycobacterial activity (MIC ≥ 12.5 μg/ml). The compounds also reduced chlorophyll content in green algaChlorella vulgaris, and some of them inhibited photosynthetic electron transport in spinach chloroplasts as well. The photosynthesis-inhibiting activity of nitro derivatives was lower than that of the corresponding hydroxylated analogues.

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.

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.