Synthesis, Characterization and Biological Activity of Dimethyltin Dicarboxylates Containing Germanium

A series of diorganotin dicarboxylates of the general formula (CH3)2Sn(OCOCHR3CHR2GeR1)2 where R1=(C6H5)3, (P-CH3C6H4)3, N(CH2CH2O)3, R2=C6H5, H, CH3, P-CH3OC6H4, P-ClC6H4, P-CH3C6H4, R3=CH3 and H, have been synthesized by the reaction of dimethyltin oxide with germanium substituted propionic acid in 1:2 molar ratio in toluene. The H2O formed was removed azeotropically using a Dean and Stark apparatus. All the compounds have been characterized by IR, multinuclear (1H, 13C, 119Sn) NMR, mass and Mössbauer spectroscopies. All compounds were found to have potential activity against bacteria.


Introduction
Organotin chemistry has been the subject of much interest in recent years. The importance of this area of main group organometallic chemistry is in part a result of their various industrial and agricultural applications. In addition, they have been reported as having potential antitumor activities. These are well cited in the literature [1-]. For example, organotin carboxylates have been reported by Gielen et. al to have promising activity against various antitumour cells [5]. Furthermore, Crowe et. al stated that the R2Sn 2+ moiety is the active portion of the diorganotin, RSnXY, molecules. The function of the XY groups in these compounds is to transport the potentially active RSn + moiety to the site of action where it is released by hydrolysis [4].
There has been considerable interest in recent years in the chemistry of bioactive germanium compounds. The first organogermanium pharmaceutical propagermaniurn was launched in Japan in 1994. Its biological activity spectrum modules the protection against viruses, irnmunostimulation and hepatoprolation [6][7][8][9][10] ]. In the present work, we are reporting the synthesis of several germatranyl and triaryl germyl substituted propionic acids and their reactions with dimethyltin oxide. Compound I was found to be more active for Bacillus cerus and Klebslella pneumoniae than the reference drugs. EXPERIMENTAL

Synthesis of Compounds
Germanium-substituted propionic acids were prepared according to the literature 11 using Scheme 1. The germanium-substituted dimethyltin dipropionates were then synthesized by the condensation of dimethyltin oxide and germanium substituted propionic acids in a 1.'2 molar ratio in toluene/ethanol (3"1). The general reaction is shown as follows: The following is a typical procedure for the synthesis of the dimethyltin germanium substituted carboxylates: 0.005 Mole of dimethyltin oxide and 0.01 moles of appropriate germanium substituted propionic acids were suspended in a ethanol:toluene mixture (1:3) and refluxed for 10 hours. The water formed during the reaction was removed by a Dean and Stark apparatus. The solvent was removed under vacuum and the solid thus obtained was recrystallized from a chloroform:petroleum ether mixture (1"1). The yields and physical data are listed in Table 1.

Spectra
The infrared spectra were recorded as KBr discs on a Hitachi model 270-1117 spectrophotometer. PMR spectra were recorded in CDC13 on a Bruker SF 300 or SF 400 spectrometer using TMS as the internal rerence. A Jeol FX90Q instrument using Me4Sn as the external reference was used to record the ''Sn NMR. The mass spectral data were measured on a JMS-DX 300 mass spectrometer. The M/Sssbauer spectra were measured at 80K on a Ranger Model MS-900 MSssbauer spectrometer in the acceleration mode with a moving source geometry using a liquid nitrogen cryostat. The samples were mounted in Teflon holders. The source was 5 mCi Synthesis, Characterization and Biological Activity of Dimethyltin Dicarboxylates Containing Germanium Call9mSnO3, and the velocity was calibrated at ambient temperature using a composition of BaSnO3 and Sn foil (splitting-2.52 mm s ). The resultant spectra were analyzed by a least-square fit to Lorenzian shaped lines.

Antibacterial activity
The agar well diffusion technique was adopted for determining the antibacterial activity of the test compounds. Two mg/mL of the test solution were added to their respective wells. Other wells supplemented with DMSO and reference antibacterial drugs were used as 1)egat6ive and positive controls, respectively. The bacterial inocula (2-8 hours old) containing ca. 10"-10 colony forming units (CFU)/mL were then spread on the surface of the nutrient agar plates using a sterile cotton swab. The plates were incubated immediately at 37C for 14-19 hours. After the incubation period, the zones of inhibition were calculated.

Infrared spectra
The infrared spectra of the compounds have been recorded in the range of 4000-400 cm and the absorptions of interest are reported in Table 2 It has been reported that the shifting of the ravin(COO) vibration to a lower frequency coupled with the shifting of the Vsym(COO) vibration to a higher frequency for the carboxylate group when compared to the ionic carboxylate values is indicative of a bidentate carboxylate group. For unidentate coordination of the carboxylate group the reverse is true [14]. Thus, the mode of coordination of the carboxylate group has been related to the magnitude of the separation (Av) of the Vaym(COO) and 'ym(COO) vibrations [14]. In compounds (I-X), the Av values in the solid are between 170-202 cm-. This range of Av values is indicative of carboxylate groups that behave as a bidentate ligand.
The observation of both the Sn-C symmetric and asymmetric vibrations would indicate the C-Sn-C moiety is not linear. Based on these two observations the compounds are six-coordinated with non linear methyl groups in the solid state.

MOssbauer spectra
Indirect evidence for solid state structures of organotin compounds can also be derived from Mtissbauer spectroscopy. In this context, the most useful parameter is the quadruple splitting (QS) for which a given range is associated with a particular coordination number and geometry at the tin atom. M6ssbauer data for compounds II and III have QS values of 3.47 and 3.32 mm s -, respectively. This range of values suggests a trans RSn(OCR)_ structure with chelated carboxylate groups. Thus, the structures of the compounds in the solid state are hexacoordinated which is in agreement with the infrared results.

NMR spectra
The proton NMR spectral data of the complexes are given in Table 3. The observed resonances and patterns are in agreement with those expected for the titled compounds. The integrations of the spectra are in good agreement with the expected values for the protons in the complex molecules. Furthermore, the proton NMR spectra, in CDCI3, of the cyclic skeleton of the simple germatranes consisted of two triplets (A2B2 spin system) at 2.23-2.83 ppm for the NCH_ and 3.68-3.73 ppm for the OCH protons. This pattern is the general feature for the atrane framework [15]. The relative values of the vicinal coupling constant are in the range of 3jAB (6 Hz) and are consistent with the atrane framework 15].
In compounds (I-X), the methyl groups attached directly to tin atom absorbed in the range of 0.23-0.98 ppm and appears as a sharp singlet with J(9Sn-IH) values ranging from 56 to 84 Hz.
A particular advantage of methyltin derivatives is the ease with which proton spin-spin coupling constant can be determined. The coupling constants have been related to the hybridization state of the tin atom and has been reported to increase with an increase in coordination number [16]. The Sn-IH) + 133.4 [17]. Using this criterion, the estimated bond angles for the compounds in solution range from 106 to 136. This magnitude for the C-Sn-C bond angles has been reported in the literature for methyl compounds as being 5 or 6 coordinated 17].
The 3C NMR spectral data are given in Table 4. The methyl carbon attached to tin atom absorbs in the range of 5 to 19 ppm. In the germatrane derivatives, the carbon atoms attached to the ermanium atom through the OCH and NCH_ groups resonate at 56 and 51 ppm, respectively. The C positions of the substituents on the phenyl rings are reported in parenthesis ( Table 4). The CH group attached to the COO group was observed to absorb at a lower field as compared to the CH group attached to the germanium atom (Table 4) Listed in Table 4 are also the llgsn NMR data. The ll9Sn chemical shifts cover a range of approximately 6500 ppm depending upon the coordination number [22]. It is generally accepted that the compounds with different geometries about the tin atom produce shifts in moderately well defined ranges. The range is between +200 to -60 ppm for four coordinated compounds and from -90 to -330 ppm for five coordinated systems and -125 to -515ppm for hexacoordi  Mass spectra Main fragment ions observed in the mass spectra of compounds (I-X) are listed in Table 5.
The germatranyl substituted compounds have a base peak at 220 which is due to the N(CHCHO)3Ge + species while aryl substituted germanium compounds give base peaks fragments for Ph3Ge + or (CH3C6H4)3Ge+. However, the molecular ion peak was not found in any of the compounds. Also, the isotopic effects have been observed in all the fragmentation ions containing germanium and tin.
In the mass spectra of the germatrane compounds, the peak of highest intensity is at m/z 220 which corresponds to the germatranyl ion. This is a result of the cleavage of the germanium carbon bond in the parent ion. This behavior is analogous to that observed for 1-allylgermatrane and 1-fluorenyl germatrane [24] and is assumed to be a reflection of the relative strength of the germantrane skeleton.
In the mass spectral fragmentation of aryl-substituted germaniums R3Ge (where R C6H5 and CH3C6H4), the peak of highest intensity is found at 305 and 347, respectively. The successive loss of the aryl gro+ups takes place as given below:  The bactericide study results using compounds I V as the toxicant are given in Table 6. In general, most of the compounds had similar activity to the various bacteria as the two reference drugs, Amoxicillin and Ampicillin. However in a few cases, the activities of the compounds were slightly higher than those observed for the reference drugs. For example, compound I was found to be more active for Bacillus cerus and Klebslella pneumoniae than the reference drugs. All compounds have shown good activity against all pesto bacteria. The mechanisms involve in the bactericidal effect of these compounds have not been discerned. However, the site of action of the reference antibiotics is the cell wall. Bacteria used in this study were both gram negative and gram positive. It is well established that antibiotics that influence cell wall synthesis do not destroy gram negative bacteria. Thus, it would be of interest to investigate the effects of the dimethyltin dicarboxylates on both gram positive and gram negative bacteria. If there is a propensity of these compounds to effect the destruction of gram negative or antibiotic resistant bacteria that are unaffected by most antibiotics, then the possible use of these compounds in treating diseases caused by gram negative bacteria should be examined.