Ligational Behavior of Synthesized New Hydrazones Towards Oxovanadium (IV) Complexes and Their Antituberculosis Aspects

- The synthesis of some oxovanadium (IV) complexes with bidentate ligands (new synthesized biologically active hydrazones) derived from 2-methyl-4-(N-cyanoethyl)-N-benzenesulphonyl-benzylidene-3-oxo- [N-(substituted-1-phenyl)propanamido] hydrazone were analyzed. The complexes prepared were of the type [VO.L 2 ] (where L= different new synthesized hydrazones).The characterization of these newly synthesized hydrazones and their metal complexes were done by IR, 1 H-NMR spectral studies and elemental analysis. The infrared data of these complexes revealed the bidentate nature of the ligands and coordination to imino nitrogen of the amido group and azomethinic-nitrogen atoms. The new products were synthesized and evaluated for anti-tuberculosis activity against Mycobacterium tuberculosis H 37 R V in L.J.medium. The biological screening data indicates that the metal chelates are more potent than the parent ligands.


I. INTRODUCTION
Hydrazone compounds obtained by the reaction of aromatic and heterocyclic hydrazides with mono-and di-aldehydes or ketones have revealed very versatile behavior in metal coordination 1  Hydrazones play an important role in inorganic chemistry as they easily form stable complexes with most transition metal ions in the periodic table the development of the field of bioinorganic chemistry has increased the interest in hydrazone complexes, as they have been recognized that many of these complexes may serve as models for biologically important species. The remarkable biological activity of acid hydrazides R-CO-NH-NH2, their corresponding hydrazones, R-CO-NH-N=CH-R ' and the dependence of their mode of chelation with transition metal ions present in the living system, have been of significant interest in the past [3][4][5][6] . The coordination compounds of aroylhydrazones have been reported to act as enzyme inhibitors 7 and are useful due to their pharmacological application [8][9][10] . Isonicotinic acid hydrazide is a drug of proven therapeutic importance and used against a wide spectrum of bacterial ailments, as tuberculosis 11 .
Hydrazones have been studied as a group of the most useful spectrophotometric reagents 2,12,13 . Combining appropriate starting materials (carbonyl compounds and hydrazine), the sensitivity as an analytical reagent and / or solubility of the hydrazones could be improved and the donating environment could be changed. The shortcoming of hydrazones was their lack of selectivity 2 for metal ions. Much effort has been devoted to developing masking agents for use with hydrazones 14,15 .
High-performance liquid chromatography (HPLC) of metal chelates 16 is a promising alternative approach for overcoming the lack of selectivity of the chelating reagents 2 . hydrazone ligands and their complexes have been studied for their antifungal and antibacterial activity, as iron chelators in the treatment of anemias and as antiviral drugs 1 .
The coordination chemistry of oxovanadium (IV) with multidentate ligands is important due to its growing application in catalysis 17 and therapeutics 18 .Vanadium in traces has multiple biological roles, therapeutic value in small doses and toxic in excess. Vanadium containing compounds have their utility as insulin mimetic 19 and antiamoebic agent 20 .
It is also suggested that vanadium could be considered as a representative of a new class of non-platinum metal antitumour agents21. In the present investigation we describe the synthesis and characterization of some new hydrazones and their oxovanadium (IV) complexes.

III. RESULTS AND DISCUSSION
All compounds gave satisfactory results for elemental analysis, IR and 1 H-NMR spectra. The physical and analytical data of synthesized new hydrazones and their metal complexes are presented in table-1. A strong band around 1630 cm -1 indicates the formation of new hydrazone because this band appears due to condensation of hydrazide with aldehyde, when these hydrazones chelate with metals, the normal frequency of ν (C=O) stretching band is shifted towards lower frequency region. In all the complexes of VO 2+ , the V = O (oxovanadium) stretching frequency occurs in the range 975-960 cm -1 . These values are in the range observed for monomeric VO 2+ complexes 22 . The dπ -pπ orbital overlap involved in a multiple bond. This strong multiple bonding with the oxygen appears to be responsible for the trans influence of the oxo ligand , which disfavors attachment of a ligand trans to O 23 . The protin of azomethine group (CH = N) sharp peak is observed at δ 8.50 -8.80 ppm . Further two signals observed at δ 3.60 -3.90 ppm are assigned to methylene protons 25 . The multiplet due to aromatic protons appears in the δ 7.03 -8.30 ppm region. The appearance of two doublets in the region δ 11.11 -12.96 ppm coupled with signals at δ 3.60 -3.90 ppm suggests enolization of hydrazones involving active methylene group with keto-enol equilibrium in the solution. Thus, the signal at δ 3.60 ppm may be attributed to methylene (-CH2-) and that at δ 3.90 ppm to methane proton (=CH-).
The bonding of ligand to metal is further supported by 1 H-NMR spectral studies and NMR spectra (Table 3)   Moreover, the compounds Ia and Iib exhibited a moderate activity (MIC 250 μg/ml). However, the compound having codes as Ib showed mild activity (MIC 500 μg/ml).
In the present study small number of isolates (n = 04) were tested for their antitubercular susceptibility.
It would be appropriate to study the same impact of the synthesized new compounds on a still larger number of isolates obtained from variety of clinical samples, so as to study the spectrum of effectivity of these compounds.
With the increasing number of multi-drug resistance of M. tuberculosis, it is desirable to start anti-tubercular therapy only after sensitivity assay to determine the most suitable drug against particular isolate infecting to patient. Moreover, with increasing prevalence of tuberculosis, there is a need of regular development of newer and newer anti tubercular drugs for the effective management of tuberculosis in patients, thus here lies the importance of the investigated compounds of organic origin.

V. CONCLUSION
In this paper coordination chemistry of a newly synthesized hydrazone ligands , obtained from the reaction of 3-oxo-[ N-(substituted -1-phenyl) propanamido ] hydrazide and 2methyl-4-( N-cyanoethyl )-N-benzenesulphonyl benzaldehyde , is described . Oxovanadium (IV) complexes have been synthesized using the above newly hydrazone ligands and characterized on the basis of analytical, IR 1 H-NMR spectral data. The observation of newly hydrazone ligand to the metal ion through imino nitrogen of the amido group and azomethine nitrogen and acts as a bidentate ligand. In all the synthesized metal complexes of vanadium metal attached oxygen atom to monomeric (VO +2 ) form because of the dπ-pπ orbital overlap involved in a multiple bond. This strong multiple bonding with the oxygen appears to be responsible for the trans-influence of the oxo-ligand, which disfavors attachment of a ligand trans to oxygen.
The biological screening data of indicare that the metal chelates are more potent than the parent ligands.

VI. EXPERIMENTAL Materials and Instrumentation:
All reagents used were purchased from Merck and used as received. Melting points were taken in open capillary and are uncorrected. Elemental analyses, 1 H-NMR spectra were obtained on a Bruker FT-400 spectometer using CDCl3 as solvent and TMS as an internal standard. IR spectra were recorded on KBr disks, using a Jasco-410 FTIR spectrometer. All the hydrazides were prepared by the reaction of hydrazine hydrate with different esters.

(B) Preparation of the metal complexes of MCPH and MNPH :
To a hot solution of the respective metal salt [0.173gm vanadyl chloride (VOCl2.2H2O)] in methanol was added a sufficient amount of the MCPH (0.538 gm) or MNPH (0.548 gm) . The solution was mixed with a required stoichiometric amount of the respective ligand in hot methanol. The resulting mixture was refluxed for four hours and then concentrated to half of its volume. On cooling, a colored crystalline product was obtained , which was filtered , washed with organic solvents and dried in a vaccum oven .

(C) Biological experiments:
A series of newly synthesized compounds have been tested for their anti-tubercular effect on M. tuberculosis [28][29][30] . Four different strains of M.tuberculosis isolated from various clinical specimens belonging to pulmonary and extrapulmonary patients (sputum, pleural fluid, pus and lymph node aspirate). Standard strain of M. tuberculosis i.e. (H37RV) was used as control strain. All test compounds of varying concentration ranging from 1600 μg/ml -50 μg/ml. The L .J. Media containing different test compounds were brought at room temperature . 100 μl of seed culture was applied to each slant of L. J. Medium containing different test compounds. A fresh disposable loop was used for each slant. The cap was closed tightly and slants were incubated at 37±0.5 0 C.
All the cultures, incubated at 37 0 C were observed initially twice in a week for a period of three weeks and later weekly for a total period of eight weeks for the growth of AFB. Results were noted according to the minimum effective concentration inhibiting the growth of AFB on the medium.