Differences in the Structure and Antimicrobial Activity of Hydrazones Derived from Methyl 4-Phenylpicolinimidate.

Four novel methyl 4-phenylpicolinoimidate derivatives of hydrazone have been synthesized and evaluated for their antimicrobial activity, including tuberculostatic activity. The compounds obtained are condensates of hydrazonamide or hydrazide with 5-nitro-2-furaldehyde or 5-nitro-2-thiophenecarboxaldehyde. The antimicrobial activity of the tested compounds varied. Compound 3b exhibited significant activity against the tested Gram-positive bacteria (7.8-250 µg/mL). The results of structural tests revealed that the compound is the only one obtained in the form of a Z isomer. Tuberculostatic activity tests showed higher activity of derivatives 3a and 4a containing nitrofuran systems (MICs 3.1-12.5 µg/mL). This research allowed us to identify hydrazone 3b as a starting point for further optimization in the search for antimicrobial drugs. Likewise, compound 4a appears to be a good guiding structure for use in future research on new anti-tuberculosis drugs.

Relationship between the Crystal Structure and Tuberculostatic Activity of Some 2-Amidinothiosemicarbazone Derivatives of Pyridine.

Tuberculosis remains one of the most common diseases affecting developing countries due to difficult living conditions, the rapidly increasing resistance of M. tuberculosis strains and the small number of effective anti-tuberculosis drugs. This study concerns the relationship between molecular structure observed in a solid-state by X-ray diffraction and the 15N NMR of a group of pyridine derivatives, from which promising activity against M. tuberculosis was reported earlier. It was found that the compounds exist in two tautomeric forms: neutral and zwitterionic. The latter form forced the molecules to adopt a stable, unique, flat frame due to conjugation and the intramolecular hydrogen bond system. As the compounds exist in a zwitterionic form in the crystal state generally showing higher activity against tuberculosis, it may indicate that this geometry of molecules is the "active" form.

The structures of benzimidazole derivatives and their potential as tuberculostatics.

Tuberculosis still remains a very important problem, especially its multidrug resistant varieties (MDR-TB). Among the potential tuberculostatics, there are two benzimidazole derivatives, namely 5,6-dimethyl-2-phenylethylbenzo[d]imidazole (1) and (E)-5,6-dimethyl-2-styryl-1H-benzo[d]imidazole (2) which showed significant tuberculostatic activities, better than those of Pyrazinamide and Isoniazyd. Also, the cytotoxicity of 1 appeared promising. The compounds were studied (with the use of X-ray diffraction) in the form of the hemihydrate of 1, C17H18N2·0.5H2O (1a), the methanol hemisolvate of 2, C17H16N2·0.5CH3OH (2a), and the acid oxalate salt of 2, namely (E)-5,6-dimethyl-2-styryl-1H-benzo[d]imidazolium hydrogen oxalate, C17H17N2+·C2HO4- (2b). All three structures reveal a similar extended conformation, despite the flexible linker between the two aromatic systems and the different types of strong intermolecular hydrogen bonds. The molecules of 2a are practically planar due to the double bond in the linker, which enables conjugation along the whole molecule, while the molecules of 1a exhibit the possibility of parallel orientations of their aromatic systems, despite the aliphatic (ethyl) linker.

Planarity of benzoylthiocarbazate tuberculostatics. IV. Polymorphs of N'-(1,3-dithiolan-2-ylidene)-4-nitrobenzohydrazide.

The search for new tuberculostatics is important considering the occurrence of drug-resistant strains of Mycobacterium tuberculosis. Three polymorphs of N'-(1,3-dithiolan-2-ylidene)-4-nitrobenzohydrazide (a potentially tuberculostatic agent), C10H9N3O3S2, denoted (I1), (I2) and (I3), and the monohydrate of this compound, C10H9N3O3S2·H2O, (I4), have been characterized by single-crystal X-ray diffraction. The conformations of the molecules in all these structures are very similar. Structures (I1), (I2) and (I3) provide an example of packing polymorphism resulting from different intermolecular interactions.

Planarity of benzoylthiocarbazate tuberculostatics. III. Diesters of 3-(2-hydroxybenzoyl)dithiocarbazic acid.

Searches for new tuberculostatic agents are important considering the occurrence of drug-resistant strains of Mycobacterium tuberculosis. The structures of three new potentially tuberculostatic compounds, namely isopropyl methyl (2-hydroxybenzoyl)carbonohydrazonodithioate, C12H16N2O2S2, (Z)-benzyl methyl (2-hydroxybenzoyl)carbonohydrazonodithioate, C16H16N2O2S2, and dibenzyl (2-hydroxybenzoyl)carbonohydrazonodithioate propan-2-ol monosolvate, C22H20N2O2S2·C3H8O, were determined by X-ray diffraction. The mutual orientation of the three main fragments of the compounds, namely an aromatic ring, a dithioester group and a hydrazide group, can influence the biological activity of the compounds. In all three of the structures studied, the C(=O)NH group is in the anti conformation. In addition, the presence of the hydroxy group in the ortho position of the aromatic ring in all three structures leads to the formation of an intramolecular hydrogen bond stabilizing the planarity of the molecules.

Planarity of benzoyldithiocarbazate tuberculostatics. II. Diesters of benzoyldithiocarbazic acid.

The emergence of drug-resistant strains of Mycobacterium tuberculosis has intensified efforts to identify new lead tuberculostatics. Our earlier studies concluded that the planarity of a molecule correlates well with its tuberculostatic activity. According to our hypothesis, only derivatives whose molecules are capable of adopting a planar conformation may show tuberculostatic activity. The structures of three new potentially tuberculostatic compounds, namely N'-[bis(methylsulfanyl)methylidene]-N-methyl-4-nitrobenzohydrazide (denoted G1), C11H13N3O3S2, N'-[bis(benzylsulfanyl)methylidene]-N-methyl-4-nitrobenzohydrazide (denoted G2), C23H21N3O3S2, and N'-[(benzylsulfanyl)(methylsulfanyl)methylidene]-4-nitrobenzohydrazide (denoted G3), C16H15N3O3S2, were determined by X-ray diffraction. The significant distortion from planarity caused by the methyl substituent at the N atom of the hydrazide group or the NO2 substituent in the aromatic ring leads to the loss of tuberculostatic activity for G1, G2 and G4 {systematic name: N'-[bis(methylsulfanyl)methylidene]-2-nitrobenzohydrazide}. A similar effect is observed when there are large substituents at the S atoms (G2 and G3).

Crystal structure of (3R)-3-benzyl-4-[(tert-but-oxy-carbon-yl)amino]-butanoic acid.

The characteristic feature of the title mol-ecule, C16H23NO4, is the syn configuration of the partially double amide C-N bond [C-N-C-O torsion angle = -14.8 (2)°]. The crystal packing is determined by inter-molecular O-H⋯O and N-H⋯O hydrogen bonds, which link the mol-ecules into a double-chain structure extending along [010].

Planarity of benzoylhydrazine-dithiocarbazoate tuberculostatics. I. N'-Methyl-substituted 3,4-dichlorobenzoyl monoesters.

Methyl 2-(3,4-dichlorobenzoyl)-1-methylhydrazinecarbodithioate, C(10)H(10)Cl(2)N(2)OS(2), (F1), butyl 2-(3,4-dichlorobenzoyl)-1-methylhydrazinecarbodithioate, C(13)H(16)Cl(2)N(2)OS(2), (F2), and 3,4-dichloro-N-(2-sulfanylidene-1,3-thiazinan-3-yl)benzamide, C(11)H(10)Cl(2)N(2)OS(2), (F3), were studied by X-ray diffraction to test our hypothesis that planarity of aryloylhydrazinedithiocarbazic acid esters is a prerequisite for tuberculostatic activity. All compounds examined in this study are inactive and nonplanar due to twists along two specific bonds in the central frame of the molecules. The significant twist at the N-N bond, with an C-N-N-C(S) torsion angle of about 85°, results from repulsion caused by a methyl substituent at the N' atom of the hydrazide group. The other twist is that within the benzoyl group at the C(O)-Ph bond, i.e. the N-C(=O)-C(phenyl)-C torsion angle: the values found in the studied structures (25-30°) are in agreement with those observed in other compounds containing a similar fragment. As some nonplanar benzoyl derivatives are active, it seems that planarity of the hydrazinedithioate fragment is more important for tuberculostatic activity than planarity of the aryloyl group.

Planarity of heteroaryldithiocarbazic acid derivatives showing tuberculostatic activity. IV. Diesters of benzoylcarbonohydrazonodithioic acid.

Dimethyl (3,4-dichlorobenzoyl)carbonohydrazonodithioate, C(10)H(10)Cl(2)N(2)OS(2), (D1), dibenzyl (3,4-dichlorobenzoyl)carbonohydrazonodithioate, C(22)H(18)Cl(2)N(2)OS(2), (D2), dimethyl (3,4-dichlorobenzoyl)-1-methylcarbonohydrazonodithioate, C(11)H(12)Cl(2)N(2)OS(2), (D3), 3,4-dichloro-N'-(1,3-dithiolan-2-ylidene)-N-methylbenzohydrazide, C(11)H(10)Cl(2)N(2)OS(2), (D4), were synthesized as potential tuberculostatics. Compound (D1) (with two molecules in the asymmetric unit) was the only one showing tuberculostatic activity of the same range as the common drugs isoniazid and pyrazinamide. The molecular structures of the studied compounds depend on the substitution at the N atom adjacent to the carbonyl group. In the case of the unsubstituted derivatives (D1) and (D2), their central frames are generally planar with a twist of the 3,4-dichlorophenyl ring by 30-40°. Until now, coplanarity of the aromatic ring with the (methylene)carbonohydrazone fragment has been considered a prerequisite for tuberculostatic activity. The N-methylated derivatives (D3) and (D4) show an additional twist along the N-C(=O) bond by 20-30° due to the spatial repulsion introduced by the methyl substituent.

Synthesis, characterization, and tuberculostatic activity of novel 2-(4-nitrobenzoyl)hydrazinecarbodithioic acid derivatives.

ABSTRACT: A series of novel S-esters of 2-(4-nitrobenzoyl)hydrazinecarbodithioic acid and S,S'-diesters of (4-nitrobenzoyl)carbonohydrazonodithioic acid were synthesized by reaction of 4-nitrobenzohydrazide and N-methyl-4-nitrobenzohydrazide with carbon disulfide and alkyl halides in the presence of triethylamine. Novel 5-(4-nitrophenyl)-1,3,4-oxadiazoles were also obtained. The structures were confirmed by IR, NMR, and mass spectroscopy, and by elemental analysis. All the compounds obtained were screened in vitro for their tuberculostatic activity. Promising preliminary results were obtained for some of the compounds. The crystal structure of the most active compound was determined.

Planarity of heteroaryldithiocarbazic acid derivatives showing tuberculostatic activity. III. Mono- and diesters of 3-(pyrazin-2-ylcarbonyl)dithiocarbazic acid.

Methyl 2-(pyrazin-2-ylcarbonyl)hydrazinecarbodithioate, C(7)H(8)N(4)OS(2), (E1), N'-[bis(methylsulfanyl)methylidene]pyrazine-2-carbohydrazide, C(8)H(10)N(4)OS(2), (F1), N'-[bis(methylsulfanyl)methylidene]-6-methoxypyrazine-2-carbohydrazide, C(9)H(12)N(4)O(2)S(2), (F2), and methyl 1-methyl-2-(pyrazin-2-ylcarbonyl)hydrazinecarbodithioate, C(8)H(10)N(4)OS(2), (G1), can be considered as derivatives of classical (thio)amide-type tuberculostatics, and all are moderately active against Mycobacterium tuberculosis. This study was undertaken in a search for relationships between activity and specific intramolecular interactions, especially conjugations and hydrogen-bond contacts, and the molecular structures were compared with respective amine analogues, also active against the pathogen. Despite the differences between the amine and carbonyl groups with opposite functions in the hydrogen bond, the two types of structure show a surprisingly similar planar geometry, mostly due to the conjugations aided by the bifurcated intramolecular hydrogen-bond contact between the N-H group of the central hydrazide group as donor and a pyrazine N atom and an S atom of the dithio function as acceptors. Planarity was suggested to be crucial for the tuberculostatic activity of these compounds. The N-methylated derivative (G1) showed a significant twist at the N-N bond [torsion angle = -121.9 (3)°] due to the methyl substitution, which precludes an intramolecular N-H···S contact and the planarity of the whole molecule. Nonetheless, the compound shows moderate tuberculostatic activity.

Synthesis and structural investigation of some pyrimido[5,4-c]quinolin-4(3H)-one derivatives with a long-chain arylpiperazine moiety as potent 5-HT(1A/2A) and 5-HT(7) receptor ligands.

A series of new pyrimido[5,4-c]quinolin-4(3H)-ones with variable length of the spacer between amide and 4-arylpiperazine moiety were prepared to further explore the role of a terminal portion in the serotonergic activity. The majority of compounds demonstrated high in vitro affinity for 5-HT(1A) receptor, and moderate-to-low affinity for 5-HT(2A) and 5-HT(7) receptors. X-ray analysis, two-dimensional NMR, conformational studies and docking into the 5-HT(1A) receptor model were conducted to investigate conformational preferences of selected 5-HT(1A) receptor ligands in different environments. The extended conformation of tetramethylene derivatives was found in a solid state, in DMSO (for a protonated form) and as a global energy minimum during conformational analysis in simulated water environment. Ligand geometry in top-scored complexes, obtained by docking to a set of 100 receptor models, were either fully extended or with central spacer torsion in synclinal conformation.

Planarity of heteroaryldithiocarbazic acid derivatives showing tuberculostatic activity. II. Crystal structures of 3-[amino(pyrazin-2-yl)methylidene]-2-methylcarbazic acid esters.

Four compounds showing moderate antituberculostatic activity have been studied to test the hypothesis that the planarity of the 2-[amino(pyrazin-2-yl)methylidene]dithiocarbazate fragment is crucial for activity. N'-Anilinopyrazine-2-carboximidamide, C(11)H(11)N(5), D1, and diethyl 2,2'-[({[amino(pyrazin-2-yl)methylidene]hydrazinylidene}methylidene)bis(sulfanediyl)]diacetate, C(14)H(19)N(5)O(4)S(2), B1, maintain planarity due to conjugation and attractive intramolecular hydrogen-bond contacts, while methyl 3-[amino(pyrazin-2-yl)methylidene]-2-methyldithiocarbazate, C(8)H(11)N(5)S(2), C1, and benzyl 3-[amino(pyrazin-2-yl)methylidene]-2-methyldithiocarbazate, C(14)H(15)N(5)S(2), C2, are not planar, due to methylation at one of the N atoms of the central N-N bond. The resulting twists of the two molecular halves (parts) of C1 and C2 are indicated by torsion angles of 116.5 (2) and -135.9 (2)°, respectively, compared with values of about 180° in the crystal structures of nonsubstituted compounds. As the methylated derivatives show similar activity against Mycobacterium tuberculosis to that of the nonsubstituted derivatives, maintaining planarity does not seem to be a prerequisite for activity.

Synthesis, structure, and tuberculostatic activity of dimethyl benzoylcarbonohydrazonodithioates.

ABSTRACT: New dimethyl benzoylcarbonohydrazonodithioates were obtained by CS2 addition to arylcarboxylic acid hydrazides and methylation of the formed adduct. The new derivatives were tested for their activity against Mycobacterium tuberculosis. Some compounds exhibited high activity toward sensitive and resistant strains.

N-triazinylammonium tetrafluoroborates. A new generation of efficient coupling reagents useful for peptide synthesis.

A new generation of triazine-based coupling reagents (TBCRs), designed according to the concept of "superactive esters", was obtained by treatment of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium (DMTMM) chloride with lithium or silver tetrafluoroborate. The structure of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium tetrafluoroborate was confirmed by X-ray diffraction. Activation of carboxylic acids by using this reagent proceeds via triazine "superactive ester". The coupling reagent was successfully used for the synthesis of Z-, Boc-, and Fmoc-protected dipeptides derived from natural and unnatural sterically hindered amino acids and for fragment condensation, in 80-100% yield and with high enantiomeric purity. The manual SPPS of the ACP(65-74) peptide fragment (H-Val-Gln-Ala-Ala-Ile-Asp-Tyr-Ile-Asn-Gly-OH) proceeded significantly faster than with TBTU or HATU, as well as the automated SPPS of the same fragment gave a purer product than by using TBTU or PyBOP. The reagent was also demonstrated to be efficient in on-resin head-to-tail cyclization of constrained cyclopeptides, in SPPS synthesis of Aib peptides, and in the synthesis of esters from appropriate acids, alcohols, and phenols. The high efficiency and versatility of this new generation of TBCRs confirm, for the first time, the usefulness of the concept of "superactive esters" in rational design of the structure of coupling reagents.