Synthesis , Structure and Biological Activity of Some Diorganotin ( IV ) with Benzamidomethionine

New series of diorganotin(IV) complexes of the type Ph2SnL2, Bu2SnL2 and Me2SnL2 of the ligand benzamidomethionine (LH). Ligand formed by reaction of benzoyl chloride with methionine in presence of sodium hydroxide. The prepared complexes were characterized by elemental analysis, infrared, conductance measurements and nuclear magnetic resonance (NMR and NMR) spectral data. From the spectral measurements, monomer structures for the complexes were proposed. Bidentate and Octahedral geometry was proposed for the complexes prepared. Preliminary in vitro tests for fungicidal activity show that all prepared compounds display good activity to Gibberela, Cercospora arachidicola, Physolospora piricola and Fusarium oxysporum. Moreover, the Ph2SnL2 show a higher inhibition percentage then diorganotin carboxylate.


Introduction
The chemistry of organotin(IV) complexes has developed considerably during the last 30 years, organotin compounds in general and organotin carboxylates in particular continues to grow because of their biological activity and potential antineoplastic and antituberculosism agents (Zhang et al., 2007;Tian et al., 2005;Nathm et al., 2005), PVC stabilizers (Arks et al., 2005;Thoonen et al., 2004;Kuzelova and Vymazal 1999) and anti-tumour drugs (Tabassum and Pettinari 2006) as well a polymer catalysts (Angiolini et al., 2008) .

Synthesis of benzamidomethionine
A one gram of methionine was dissolved in (25ml) of 5% NaOH solution in a conical flask.To this mixture benzoyl chloride (2.25ml) was added in a five portions and shaked vigorously until all the chloride has reacted.Acidified with diluted hydrochloric acid and the crude product was washed with cold ether.Finally, the desired product was recrystallized from Ethanol.

Preparation of Complexes
Complexes were synthesized by dissolving the free ligand (2 mmol) in hot toluene and adding the diorganotin salts (1 mmol) to the solution.The solution was refluxed for 6 hours with magnetic stirrer and then cooled and filtered.The filtrate was reduced under vacuum to a small volume and solid was precipitated by the added of petroleum ether, dried at 60 ºC and recrystallized from Ethanol.

Instrumentation
Elemental C, H and N analysis were carried out on a Fison EA 1108 analyzer, the FTIR spectra in the range (4000-370) cm -1 cut were recorded as potassium bromide discs using a Perkin-Elmer spectrophotometer GX, molar conductance measurements were made in anhydrous DMF at 25 o C using Inolop-Cond Level 1 WTW, atomic absorption measurements of the prepared complexes were obtained using Shimadzu 680cc-flame.The 1 H and 13 C nuclear magnetic resonance spectra were recorded on a jeol 400 MHz spectrometer, relative to the internal standard tetramethylsilane (TMS).Melting points were determined in open capillary tubes using an electrothermal 9300 digital melting point apparatus.

Results and discussion
The ligand was prepared by the reaction of benzoyl chloride with methionine in presence of sodium hydroxide.Table (1) shows the physical data for the ligand and the prepared complexes.The purity of the ligand and its complexes were checked by TLC using silica gel-G as adsorbent.The conductance of these complexes has been recorded in DMF at room temperature in the range 8-20 ohm -1 cm 2 mol -1 , suggesting their non-electrolytic nature.The data of CHNS and Tin analysis were obtained using flame atomic absorption technique.The calculated values were in a good agreement with the experimental values.

Infra-Red Spectroscopy
The FTIR spectrum of the ligand, shows a characteristic stretching absorption bands at 3784 cm -1 , 3334 cm -1 , 1732 cm -1 1021 cm -1 and 800 cm -1 assigned to hydroxyl, N-H, carbonyl, C-O and C-S group respectively.The reaction between this ligand with Diorganotin(IV) gave different types of complexes .In the free ligand, the bands at 1732 cm -1 and 1021 cm -1 were assigned to the stretching of C=O and C-O of the hydroxyl in the carboxylate group.On complexation these bands were shifted to a lower frequency region (Masood et al., 2004).This shift is probably due to the complexation of the metal to the ligand through oxygen of the carbonyl group, the disappearance of the hydrogen from hydroxyl group on complexation indicate the complexation is through the oxygen atom.The bands for υ(Sn-C) and υ(Sn-O) are assigned in the range of (551-573) and (445-494) cm -1 respectively (Shahid et al., 2002).The IR data of the complexes are shown in Table (2).The Table lists the stretching frequency (υ) for some of the characteristics groups exhibited by the ligand and complexes.

Nuclear magnetic resonance
The 1H NMR spectra for all compounds were recorded in [ 2 H 6 ] DMSO using tetramethysilane as the internal standard.The data are compiled in Table 3.The conclusion drawn from 1H NMR studies of a few compounds lend further support to suggested formation of benzamidomethionine chelate.Ligand (L H ) give a single resonance near δ 8.69 ppm attributable to the N-H proton.The spectra also exhibit a singlet -OH peaks at 9.21 ppm due to hydroxy group.The hydroxy resonances is absent in the spectra of the complexes indicting deprotonation and coordination of Tin to the oxygen.There is a small upfield shift of the aromatic protons resonances of the ligand upon chelation with the diorganotin(IV) moiety (Shahid et al., 2002).
Table 4 shows the most relevant 13 C NMR data.Due to scant solubility of the ligand and its complexes , their spectra were recorded in [ 2 H 6 ] DMSO.The C=O resonance group of the complexes at (159.64-160.64)ppm where shifted downfield compared with the position in the free ligand which appeared at 169.64 ppm.It is most likely that shift is due to the decrease of electron density at carbon atoms when oxygen is bonded to metal ion (Masood et al., 2004).This observation lends further evidence that the complexation occurred through the oxygen atoms of the carboxylate group.
On the basis of the preceding discussion, the structure of the complexes suggested as follows:

Biological activity
Preliminary in vitro tests for fungicidal activity of ligand and complexes have been carried out by the fungi growth inhibition method (Junich et al., 1991).These compounds are dissolved in DMF at a concentration of 50 ppm.The data are summarized in Table 5, and show that all compounds display certain activity to Physolospora piricola at a low concentration.Moreover, the Ph 2 SnL 2 are more active than the other diorganotin derivatives.In addition, Ph 2 SnL 2 shows the highest inhibition percentage for Physolospora piricola (88.4%) in vitro.

Conclusion
The ligand benzamidoacetic acid was successfully synthesized.The ligand was treated to different diorganotin(IV) oxide metal salts to afford the corresponding complexes.It may concluded that the ligand coordinated through carboxylate to the Tin atom leading to the formation of four membered ring chelate.Octahedral geometry was proposed for the prepared complexes.Biological activity data have shown that the reported complexes have a significant biological activity against Gibberela, Cercospora arachidicola, Physolospora piricola and Fusarium oxysporum.

Table 1 .
Physical data for preparation ligand and the complexes prepared.

Table 4 .
13CNMR spectral data (δ,ppm) of the ligand and complexes