КООРДИНАЦИОННАЯ ХИМИЯ, 2009, том 35, № 5, с. 378-385
УДК 541.49
ORGANOBORON(IH) AND ORGANOLEAD(IV) COMPLEXES AS ANTIMICROBIAL AND ANTIMYCOBACTERIAL AGENTS: SYNTHETIC, STRUCTURAL, AND BIOLOGICAL ASPECTS
© 2009 M. Swami1, K. Mahajan1, S. Arya2, S. K. Mehla3, and R. V. Singh1*
1 Department of Chemistry, University of Rajasthan, Jaipur 302 004, India 2Department of Zoology, University of Rajasthan, Jaipur 302 004, India 3 Department of Chemistry, College of Engineering&Technology, Bikaner-334004 *E-mail: rvsjpr@hotmail.com Received April 29, 2008
Phenylboron(III) and triorganolead(IV) derivatives of the types PhB(OH)(DTCZ), PhB(DTCZ)2, and Ph3Pb(DTCZ) (where DTCZ- is the anion of a S-benzyldithiocarbazate ligand) have been synthesized by the substitution reactions of phenylboronic acid and triphenyllead chloride with S-benzyldithiocarbazate. The resulting complexes have been characterized by elemental analyses, molecular weight determinations, and conductivity measurements. The mode of bonding has been established on the basis of infrared and XH, 13C, and nB NMR spectroscopic studies. Probable tetrahedral and trigonal bipyramidal structures for the resulting derivatives have been proposed. The X-ray powder diffraction study of the compound [PhB(OH)(L1)] was carried out in order to have an idea about the molecular symmetry of the compound. The results show that the compound belongs to the orthorhombic crystal system. In the quest for better fungicides and bactericides, the studies were conducted to assess the growth inhibiting potential of the synthesized complexes against various fungal and bacterial strains. The studies demonstrate that the concentration reached levels which are sufficient to inhibit and kill the pathogens. The antimycobacterial effects of the organolead(IV) compounds were also examined. The results obtained indicated that the compounds display antimycobacterial activity.
INTRODUCTION
To overcome the alarming problem of microbial resistance to antibiotics, the discovery of novel active compounds against new targets is a matter of urgency. However, plant-based drugs have shortened the life span of the source of material. There is a continuous search for more potent and cheaper raw material to feed the industry. Coordination compounds exhibit different characteristic properties, which depend on the metal ion to which they are bound, the nature of the metal, as well as the type of ligand. These metal complexes have found extensive applications in various fields of human interest. The nature of a coordination compound depends on the metal ion and the donor atoms, as well as on the structure of the ligand and the metal-ligand interaction [1]. With increasing knowledge of the properties of functional groups, as well as the nature of donor atoms and the central metal ion, ligands with more selective chelating groups, i.e., imines or azomethines which are more commonly known as Schiff bases, are used for complex formation studies. It is reported that the rapidly developing field of bioinorganic chemistry is centered on the presence of coordination compounds in living systems [2].
Although syntheses of S-benzyldithiocarbazate Schiff bases and their complexation products were reported in the recent past [3-5], the evaluation of their biological properties has not been described. In addition, their complexes with transition metals have extensively been stud-
ied [6-8]. A variety of complexes of phenyldihydroxybo-rane with substituted dihiocarbazates were also prepared in a benzene solution. The pathogenicity of microbial infection associated with the complexes has been subjected to a variety of biointeraction studies and the results are discussed [9]. Boron complexes of benzothiazolines with NnS donor system are gaining enormous importance on account of their inherent biological potential [10]. A number of boron azomethine derivatives have been reported, and these were synthesized by the reaction of isopro-poxyborane and phenyldihydroxyborane [11].
A variety of organolead compounds possess antimicrobial and fertility regulatory activities [12-13]. The antimycobacterial activities of some lead compounds have been investigated by many of researchers in the recent past [14].
In the present work, the complexes of boron(III) and lead(IV) with different substituted S-benzyldithiocarba-zates have been synthesized. Further, their antimicrobial activity toward some clinically important bacteria and fungi was evaluated. Also, the peculiar behavior of orga-nolead complexes in chemical and biochemical processes has led us to synthesize such type of complexes and screened them for their antitubercular activity, so as to contribute in the field of bioinorganic chemistry and their clinical uses.
EXPERIMENTAL
Materials and methods. All the chemicals were dried and purified before using and the purity was checked by thin layer chromatography (TLC). All the solvents used were of high purity and distilled before use. Solvents used were dried and purified by standard methods. Glass apparatus free from moisture and fitted with quickfit interchangeable standard ground joints were used throughout the experimental work and moisture was excluded from the glass apparatus using CaCl2 drying tubes.
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Synthesis of p-chloro/nitroindolindione derivatives. First step. To a solution of chloral hydrate (0.11 mol, 18.12 g) in water (250 ml) was added a solution of p-ni-troaniline/p-chloroaniline (0.01 mol) in HCl (5.5 ml) and finally a solution of hydroxylamine hydrochloride (0.33 mol, 22.0 g) in water. The reaction mixture was heated at such a rate that vigorous boiling started within 45 min. The boiling was continued for further 10 min. The mixture was cooled when colored needles separated out. These were filtered and recrsytallized from ethanol. The synthetic procedure is shown below:
NH2
NHCOCH=NOH
o
+ HCl + CCl3CH(OH)2 + NH2OH ■ HCl Na2SOi |( )|+ NaCl + H2SO,
o
Y
p-Chloro-/nitroaniline
Y
p-Chloro-/p-nitroisonitrosoacetanilide Y = Cl/NO2
Second step. p-Nitroisonitrosoacetanilide/p-chloroi-sonitrosoacetanalide (0.05 mol) was added to the concentrated H2SO4 (50 ml) in about 30 min with constant stirring. After the addition was complete, the reaction mixture was heated at 80°C for 10 min and poured into tenfold excess of crushed ice. The resultant precipitate was filtered after an hour and dried in air. It was purified by recrystal-lization from glacial acetic acid. The cyclization reaction is shown below:
NHCOCH=NOH
Cyclization
Y
conc.H2SO4
Y
p-Chloro-/nitro-isonitrosoacetanilide
O
O
5-Chloro-/5-ni-tro-3-indolin-2-one
Synthesis of hydrazinecarbodithioic acid. To a cold solution of KOH (5.7 g) in 90% ethanol (35 ml) was added hydrazinehydrate (5 g) slowly with constant stirring. A solution of CS2 (7.6 g) was added dropwise with continuous
stirring over a period of 3 h and the temperature of reaction mixture was kept below 10°C during addition. The reaction mixture separated into two different layers. The lower oily layer was separated and dissolved in cold 40% etha-nol (40 ml). The solution was kept in ice and benzyl chloride (12.5 g) was added dropwise with stirring for 6-7 h. The dim white solid was separated by filtration. This solid was washed with distilled water and dried in air. The crude product (m.p. 118°C) was recrystallized from benzene.
Synthesis of hydrazinecarbodithioic acid ligands:
5-chloro-1H-indole-2,3-dione hydrazinecarbodithioic acid (L*H), 5-nitro-1H-indol-2,3-dione hydrazinecarbodithioic acid (L2H), and 2-hydroxy benzamidehydrazi-necarbodithioic acid (L3H2) were carried out by the condensation of 5-nitro-1H-indole-2,3-dione and 2-hydro-xybenzamide with S-benzyldithiocarbazate in an ethanol medium according to [15]. Elemental analysis data and some physical properties of these ligands are recorded in Table 1. Tautomeric forms for L1H, L2H, and L3H2 are given below:
O
HN
N
N H
S
JL
SCH2C6H5
Y
Thioketo form
2-
O
HN
SH
N
N
-SCH2C6H5
Y
Thioenol form
L1H if Y = Cl and L2H if Y = NO2, NnSH = monofunctional bidentate ligand.
Table 1. Elemental analysis data and some physical properties of these ligands
Compound F.w. (calcd/found) M.p., °C Color Contents (calcd/found), %
N S
L*H (Q6HÍ2N3OS2C1) 355.67/361.86 129 Brown 11.08/11.61 17.35/17.22
L2H (C igH 12N4O3 S 2) 369.92/372.42 155 Brownish-yellow 14.91/15.04 17.09/17.22
L3H2 (C2Ä9N3OS2) 386.89/393.52 130 Gray 10.06/10.68 16.15/16.30
S^ SCH2C6H5
HS
SCH2C6H5
OH N H
c^n'h
OH N H
Thioketo form
Thioenol form
L3H2, HOnNnSH = bifunctional tridentate ligand.
Synthesis of organoboron(III) complexes was carried out according to [16]. In a round-bottom flask (100 ml capacity) 40 ml of benzene were mixed with the calculated amount of phenyldihydroborane. The equimolar and bimolar amounts of the ligands, L1H and L2H, were added to it. To the calculated amount of the ligands dissolved in dry benzene was added dihydroxyphenylborane in unimolar and bimolar ratios. The reaction mixture was refluxed for 10-12 h on a fractionating column, and the progress of the reaction was monitored by the liberation of water/ben-
zene azeotrope. After the completion of the reaction, excess of the solvent was distilled off, and products were dried. The resulting products were washed with dry cyclo-hexane and then finally dried in vacuo for 3-4 h.
Synthesis of organolead(IV) complexes. In a round-bottom flask (100 ml capacity) 40 ml of benzene were mixed with the calculated amount of Ph3PbCl. The equimolar amount of the ligands (L1H, L2H, and L3H) was added to it. The reaction mixture was refluxed for 10-12 h and then cooled to room temperature. After the completion of the reaction, an excess of the solvent was distilled off. Then the compound was repeatedly washed with n-hexane followed by drying in vacuum for 2 h. It gave final purified solid product. The synthetic and analytical data of organoboron(III) and organolead(IV)
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