Subscribe Now Subscribe Today
Research Article
 

Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents



Harminder Kaur, Kanav Dhir, Jaspreet Kaur, Bharti Mittu and Ashish Chuhan
 
Facebook Twitter Digg Reddit Linkedin StumbleUpon E-mail
ABSTRACT

A large number of organotin complexes are used as pharmaceuticals, pesticides, stabilizers and fire retardants. In an attempt to explore its pharmaceutical profile, new diorganotin (IV) R2SnA2 (R = n-Bu, n-Oct) and triorganotin (IV) R3SnA2 (R= n-Bu) derivatives where A is the anion of 2-acetoxybenzoic acid (Aspirin), N-(4-hydroxyphenyl) acetamide (Paracetamol) and 2-(2-methyl-5-nitroimidazol-1-yl) ethanol (Metronidazole) have been synthesized. The complexes 1-9 were characterized by elemental analysis as well as FTIR, nuclear magnetic resonance (1H, 13C and 119Sn) spectroscopy. On the basis of these spectroscopic studies it is proposed that diorganotin complexes of Paracetamol and Metronidazole having 1:2 stoichiometry, show tetrahedral geometry while the complexes of Aspirin show octahedral arrangement around tin metal ion with bi-dentate nature of carboxylate group. Triorganotin complexes of Aspirin, Paracetamol and Metronidazole having 1:2 stoichiometry show trigonal bipyramidal geometry with monodentate nature of the carboxylate group around the organotin moiety in the complexes of Aspirin. The ligand molecules bound to the Sn atom through carboxyl oxygen atoms in Aspirin and hydroxyl oxygen in Paracetamol and Metronidazole. The anti-fungal activity of complexes 1, 4 and 9 has been determined against Candida albicans. It is observed that the activity increases on complexation and highest antifungal activity has been found for the triorganotin complex of metronidazole.

Services
Related Articles in ASCI
Search in Google Scholar
View Citation
Report Citation

 
  How to cite this article:

Harminder Kaur, Kanav Dhir, Jaspreet Kaur, Bharti Mittu and Ashish Chuhan, 2013. Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents. American Journal of Drug Discovery and Development, 3: 13-22.

DOI: 10.3923/ajdd.2013.13.22

URL: https://scialert.net/abstract/?doi=ajdd.2013.13.22
 
Received: September 17, 2012; Accepted: January 16, 2013; Published: April 11, 2013



INTRODUCTION

The importance of metal ions in biological system is well known as they show indispensable chemistry in various physico- chemical processes (Theophanides, 1984). Advances in understanding metal trafficking and the role of metals in curing diseases have suggested targeting metals, themselves as a useful therapeutic strategy. The success of cis-platin and its congeners suggests that metals can also be developed as therapeutic agents. cis-platin was the first in this field with its use as an anti-tumor drug (Sun et al., 2007) but it is having major disadvantage as having lower water solubility and imposing several side defects. These challenges have changed the face of current research towards non-platinum chemotherapeutics. Organometallic complexes of group 14 elements, especially tin (IV) and silicon (IV) derivatives, have been the subject of considerable interest (Casas et al., 2000; Dakternieks et al., 1997) owing to their unique physical, chemical and structural properties favorable to the environment (Ukita et al., 1999). Recently we have published few papers on the chemistry of silicon compounds and silatranes (Puri et al., 2011, 2009, 2008a). Now we are attempting to explore the chemistry of tin (IV) complexes. A large variety of organotin complexes can be prepared using multiple mechanisms of action that can prevent the development of drug resistance which is the major side effect in case of cis- platin. Organotin complexes are an active area of research owing to rich variety of their wide applications as stabilizers for PVC plastics, industrial biocides, wood preservatives and marine anti- fouling paints (Craig, 1998). In recent years, investigations have been carried out to test their antitumor activity and it has been observed that indeed several di- and tri-organotin (IV) species were found to be active against various types of cancer (Baul et al., 2009; Fei and Mun, 2007). These kinds of complexes attract particular interest in structural studies because of many possible bonding modes between the ligand and tin atom. Many di- and tri-organotin complexes were synthesized and characterized (Stefano et al., 2002). Since fast and effective relief of pain and inflammation in humans with minimum side effects continues to be a major challenge for medicinal chemistry researchers, many diorganotin (IV) derivatives have been found to have the potential to be placed in the class of non-steroidal anti-inflammatory drugs (NSAIDs) (Nath et al., 2006, 2004a, b, 2003, 1999). Organotin (IV) complexes are also used as templates which combines two functional groups of the substrate (Puri et al., 2008a, b).

As a part of our interest in to the bioinorganic chemistry of the Tin, many di- and tri-organotin derivatives with various drugs mostly non-steroidal anti-inflammatory drugs (NSAIDs) have been synthesized. These NSAIDs are frequently used medicinal drugs. Aspirin is a derivative of salicylic acid. It has analgesic, anti-inflammatory and antipyretic actions and inhibits prostaglandrin synthetase while Paracetamol is a derivative of 4-aminophenol which also has analgesic and antipyretic action. Paracetamol is useful in treatment of pain such as headache, toothache, rheumatism and neuralgia (Lawal and Obaleye, 2007). Synthesis and Characterization of complexes of Aspirin and Paracetamol has been studied with Co+2, Ni+2 and Fe+3 metal ions. Metronidazole is a derivative of nitroimidazole. It is most frequently used drug in treatment of amebiasis and trichomoniasis. Metronidazole is an antiprotozoa drug could be labeled with the 99m Tc (Ibrahim, 2009). It is useful in the treatment of infection caused by susceptible organism particularly anaerobic bacteria and protozoa. In the lieu of this, we are reporting the synthesis, spectroscopic characterization and biological activities of series of di- and triorganotin (IV) complexes of aspirin (L1H), paracetamol (L2H) and metronidazole (L3H) (Fig. 1).

MATERIALS AND METHODS

Chemistry: The interaction of R2SnO {R = Bu, Oct} and (R3Sn)2O {R = Butyl} with Aspirin, Paracetamol and Metronidazole in 1:2 (Metal:Ligand) molar ratio, leads to the formation of complexes 1-9 with an azeotropic removal of water (scheme 1). All the organotin (IV) complexes were obtained in a good yield of (67-71%) and were stable towards air and moisture. All the complexes 1-9 were identified by elemental analysis (Table 1).

Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents
Fig. 1(a-c): Chemical structure of (a) Aspirin (L1H), (b) Paracetamol (L2H) and (c) Metronidazole (L3H)

Table 1: Elemental analysis and some physical properties of organotin (IV) complexes
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

Table 2: Growth media and conditions of indicator microorganisms
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

Biological activity: The biological activity for the complexes 1-9 was studied on Candida albicans, a representative model organism used to screen the antifungal activity and six indicator strains. Indicator strains including Candida albicans were procured from different sources as few from Microbial Type Culture Collection, Chandigarh, Punjab, India. Bacteroides fragilis MTCC 1045, Candida albicans MTCC 183, Listeria monocytogenes MTCC 657 and All other cultures including Pseudomonas aeruginosa ATCC 10662, Vibrio cholera ATCC 14104 were purchased from American Type Culture Collection. Salmonella enterica is a lab isolate. To study the effect of complexes, these were dissolved in dimethyl sulfoxide chloroform/methanol/ethanol and dichloromethane and kept at 4°C till further use. The organism was cultured in sabouraud dextrose broth medium, at 30°C and then subcultured after every 36 h so as to maintain it in log phase. For all the experiments, actively proliferating log phase cells were taken and the antifungal activities of various complexes were studied by growing the cells at the final concentrations of 0.80 and 0.40 mg mL-1 in total of 2 mL culture media. 1x105 cells of Candida albicans (as counted by haemocytometer) were used per ml of the media as inoculum. Growth of cells was measured by Optical Density (OD) measurements at 600 nm. Experiments were conducted with yeast form of Candida albicans grown at 30°C in presence of above complexes at the final concentrations of 0.80 and 0.40 mg mL-1. Cell turbidity was measured after 24 h at 600 nm. Growth conditions of other organisms are mentioned in Table 2.

Percentage inhibition of tri- and diorganotin (IV) complexes are presented in Table 3. Highest Inhibitory activity (up to 80%) has been found with triorganotin complexes of Metronidazole (complex III, Fig. 2) which shows very promising results as an antifungal drug.

Table 3: Anti-fungal activity for organotin(IV) complexes of aspirin, paracetamol and metronidazole
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents
Fig. 2: Inhibition of cellular growth of the organism vs. drugs

Since, we obtained similar inhibition pattern at two different concentrations of these drugs, studies will be done to find their IC50 value.

Experimental protocols: All the di- and tri-organotin (IV) oxides were purchased from Merck, U. S. A. and were used as such. All the reactions were carried out under anhydrous conditions. The solvents used were dried before use by the methods reported in the literature (Armarego and Chai, 2003).

Preparation and characterization of the complexes: Dialkyl/trialkyltin (IV) oxide {1 mmol} and the ligands (L1H, L2H, L3H) 2 mmol were dissolved in a mixture of dry benzene (30 mL) and absolute ethanol (L1H and L2H)/methanol (L3H) (10 mL). The reaction mixture was then heated at reflux and the water removed by azeotropic distillation. The dialkyl, respectively trialkyltin (IV) oxide dissolved within 10-15 min to give a clear solution. Refluxing was further continued for 3-4 h and the contents were filtered and then cooled. Excess of solvent was removed by distillation to leave behind a solid complex. These were recrystallized from the same solvent and dried in vacuo at 40-50°C for 2-3 h. Purity of the complexes was checked by TLC using silica gel-G as adsorbent. Melting points were determined in a capillary tube on an electrothermal melting point apparatus. IR spectra for the complexes 1-9 were recorded on a Perkin Elmer FTIR spectrophotometer at 4000-200 cm-1. The 1H-NMR and 13C-NMR were recorded on a Bruker Avance II 400 NMR Spectrometer. All chemical shift values were reported with respect to TMS as internal solvent. CHN analysis of the samples was performed on the Perkin Elmer model 2400 C H N analyzer.

RESULTS AND DISCUSSION

Reaction scheme:

Scheme 1: Reaction pathway for R2Sn(Ln)2 and R3Sn(Ln)2
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

All the compounds were obtained as crystalline solids. Compounds 1 and 4 are soluble in chloroform while compound 9 is soluble in dimethyl sulfoxide while rest of the compounds are soluble in chloroform with one drop of dimethyl sulfoxide.

Spectroscopic data
Infrared spectra:
Characteristic IR frequencies (in cm-1) for organotin (IV) derivatives are presented in Table 4. The (O-H) bands which appeared in the range 2500-2800 cm-1 for the acid, were absent in the spectra of complexes 1-3 showed the deprotonation and coordination of the carboxylate anion. In complexes 1-3 Δv between vasy(COO) and vsym(COO) is important because these frequencies can be used to determine the type of bonding between metal and carboxyl group. The values of Δv can be divided in to three groups: (a) in compounds where Δv (COO)>350, hence the compounds contain the high probability of monodentate carboxylate group, (b) when Δv (COO)<200, hence the carboxylate groups of the compounds can be considered as bidentate, (c) in compounds where Δv (COO)<350 and >200 are considered as intermediate between monodentate and bidentate which is called anisobidentate. In complexes 1-3, peaks at 1602-1670 and 1335-1526 cm-1 have been assigned to vasy(COO) and vsym(COO) group.

Table 4: Characteristic IR frequencies (cm-1) of di- and triorganotin(IV) derivatives of aspirin, paracetamol and metronidazole
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

Table 5: 1H-NMR chemical shifts (δ, ppm) of di- and triorganotin (IV) complexes
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

In complexes 1 and 2, Δv value corresponds to the bidentate behavior of carboxylate group comparable to that of sodium salt while in complex 3, Δv value shows the monodentate nature of carboxylic group around the organotin moiety and is comparable to that of ester (Chandra et al., 1980). In IR spectra of the complexes 4-9, the absence of bands in 3200-3400 cm-1 region due to the hydroxyl group suggested deprotonation of this group and its subsequent coordination through the oxygen atom. The appearance of v(Sn-O) band in the region 435-515 cm-1 further confirms the complexation in 1-9. A strong absorption peak at 1370 cm-1, assigned to nitro group of free metronidazole does not suffer significant downfield shift in the spectra of complexes 7, 8 and 9 show its non-coordinating behavior in complex formation.

Multinuclear (1H, 13C and 119 Sn) NMR spectra
1H-NMR spectra:
1H-NMR spectral data of organotin (IV) complexes are presented in Table 5. The signals at 2.2, δ 3.4 and δ 11.21 ppm attributed to -OH group of hydroxyl group of metronidazole, paracetamol and carboxylic proton of aspirin, respectively, is absent in the spectra of complexes 1-9. The absence of these signals in the spectra of complexes 1-9 confirms the deprotonation of the respective groups and their subsequent coordination around organotin moiety. The -NH signal at δ 9.54 ppm in paracetamol remains unchanged which indicates that this group is not involved in the formation of complexes 4-6. The resonances due to the aromatic proton of the ring suffered a downfield shift on complex formation in 1-9. The observed downfield shift may be ascribed to the deshielding of these protons due to the drainage of electron density from ring to tin metal atom (Sagdinc and Bayari, 2004; Chen et al., 2009). All the protons in the complexes 1-9 have been identified and total number of protons calculated from the integration curves is in agreement with the proposed molecular formulae.

13C-NMR spectra: 13C-NMR spectral data along with the assignment of characteristic peaks of all the synthesized organotin (IV) complexes are presented in Table 6. The formation of the complexes 1-3 was evident from the δ (COO) value in the 13C-NMR spectra. The complexes 1-3 exhibited a δ(COO) signal in the range of 173.4-176.7 ppm which undergo downfield shift as compared to that of their parent acids (173.02 ppm), indicating the participation of the carboxylate anions in the coordination to the tin (IV) atom. This phenomenon resulted from the decrease of the electron density in the carboxylate anions upon coordinated to the tin atom moiety during complexation. The signal of the carbonyl group for aspirin and paracetamol were observed in the range of 164.4-177.7 ppm.

Table 6: 13C-NMR spectral data of di- and triorganotin (IV) complexes
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

Table 7: 119Sn-NMR spectral data of di- and triorganotin (IV) complexes (4-9)
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

No significant changes were detected in the 13C-NMR signals for complexes 1-6 upon coordination. The positions of phenyl carbon signals in the range of 115-125 ppm undergo significant downfield shift in the complexes 1-6, compared to those observed in the free aspirin and paracetamol. The presence of Sn-C peaks of butyl and octyl groups in the range of 14.1-42.7 ppm in 1-9 confirms the incorporation of organotin moiety (Sandhu and Kaur, 1990). All magnetically non-equivalent carbons of alkyl or phenyl groups attached to the tin have been identified and their chemical shifts are in close agreement with the reported values.

119Sn-NMR: The possibility of detecting the presence of coordinative different organotin (IV) moieties was explored by acquisition of 119Sn-NMR spectra. The 119Sn- chemical shifts usually cover a range, quoted relative to tetramethyltin, with increasing coordination number of tin producing a large upfield shift for δ (119Sn). In complexes 4-9, only a single peak indicates the formation of single species. In 4, 5, 7 and 8, δ value lie in range -98-56 ppm, corresponds to the tetrahedral environment (Holecek et al., 1986; Kapoor et al., 2003) around the tin atom while in 6 and 9, δ value lie in range -132 to -142 ppm, corresponds to the trigonal bipyramidal geometry (Table 7).

Biological activity: The biological activity for the complexes 1-9 was studied on Candida albicans, a representative model organism used to screen the antifungal activity and six indicator strains results of all the 9 drugs complexes (Table 8) are as Complex 1 and two are give good inhibition against all the six strains and two different concentration 100 and 500 ppm have been used. Complex 3 have not shown any inhibition against Listeria monocytogenes MTCC 657 and Bacteroides fragilis MTCC 1045 even at 500 ppm of drug. Complexs 4 and 7 have not shown any inhibition against Listeria monocytogenes MTCC 657 and Bacteroides fragilis MTCC 1045 at 100 pm but it has shown good results with 500 ppm.

Table 8: Zone of inhibition for organotin complexes against various strains
Image for - Synthesis and Evaluation of Diorganotin(IV) and Triorganotin(IV) Derivatives of Aspirin, Paracetamol and Metronidazole as Antimicrobial Agents

Good inhibition zones were observed by Complexes 5, 6 8, 9. Maximum zone of 24 mm was observed be complex 6 and 9 against Salmonella enterica. the antifungal activities of various complexes were studied by growing the cells at the final concentrations of 0.80 and 0.40 mg mL-1 in total of 2 mL culture media. The 1x105 cells of Candida albicans (as counted by haemocytometer) were used per mL of the media as inoculum. Growth of cells was measured by OD measurements at 600 nm.

Percentage inhibition of tri- and diorganotin (IV) complexes are presented in Table 7. Highest Inhibitory activity (up to 80%) has been found with triorganotin complexes of Metronidazole (complex III, Fig. 1) which shows very promising results as an antifungal drug. Since, we obtained similar inhibition pattern at two different concentrations of these drugs, studies will be done to find their IC50 value.

CONCLUSIONS

Organotin (IV) complexes of Aspirin, Paracetamol and Metronidazole have been synthesized in 1:2 (Metal: Ligand) molar ratio through azeotropic removal of water. The spectral studies of complexes 1-9 suggest a tetrahedral geometry in diorganotin complexes of Paracetamol and Metronidazole while octahedral environment around tin metal ion in the complexes of Aspirin. In triorganotin complexes of Aspirin, Paracetamol and Metronidazole, trigonal bipyramidal geometry is observed. The anti-fungal activity of all the studied complexes revealed that the activity increases on complexation and it has been observed that the highest antifungal activity has been found for the triorganotin complex of metronidazole. The results obtained from zone of inhibition method are in same lines with those observed from turbidity method. Zone of inhibition (Table 8) increases with increasing concentration of drugs except in one strain Listeria monocytogenes MTCC 657.

ACKNOWLEDGMENT

Dr. J.K. Puri former professor and Head Inorganic Chemistry, Panjab University Chandigarh is thankful to the University Grant Commission for the award of Emeritus Professor fellow 2010 in order to continue his research.

REFERENCES

  1. Armarego, W.L.F. and C.L.L. Chai, 2003. Purification of Laboratory Chemicals. 5th Edn., Butterworth Heinemann, London, UK


  2. Baul, T.S.B., S. Basu, D. de Vos and A. Linden, 2009. Amino acetate functionalized Schiff base organotin(IV) complexes as anticancer drugs: Synthesis, structural characterization and in vitro cytotoxicity studies. Invest. New Drugs, 27: 419-431.
    CrossRef  |  


  3. Casas, J.S., A. Castineiras, F. Condori, M.D. Couce and U. Russo et al., 2000. Reaction of the diethyltin(IV) cation with pyridoxine (PN, vitamin B6) in the presence of various anionic species: The crystal structure of [SnEt2 (PN-H)]Cl. Polyhedron, 19: 813-819.
    CrossRef  |  


  4. Chandra, K., R.K. Sharma, B.S. Garg and R.P. Singh, 1980. Preparation and characterization of carboxylato derivatives of bis-(methyl cyclopentadienyl) titanium (IV). J. Inorg. Nuclear Chem., 42: 187-193.
    CrossRef  |  


  5. Chen, C., K. Chen, Q. Long, M. Ma and F. Ding, 2009. Structural characterization and DNA-binding properties of Sm(III) complex with ofloxacin using spectroscopic methods. Spectroscopy: Int. J., 23: 103-111.
    CrossRef  |  


  6. Fei, C.C. and L.K. Mun, 2007. Cytotoxicity and structure-activity relationship studies of aqua-triphenyltin(IV) carboxylates on human cancer cell lines. Main Group Met. Chem., 30: 107-116.
    CrossRef  |  


  7. Craig, P.J., 1998. Book review: Tributyltin: Case study of an environmental contaminant. S.J. De Mora (Ed). Cambridge University Press, Cambridge, 1996. 301 pages. £50, hardback. ISBN 0-521-47046-3. Applied Organomet. Chem., 12: 298-299.
    CrossRef  |  Direct Link  |  


  8. Dakternieks, D., K. Jurkschat, S. van Dreumel and E.R. Tiekink, 1997. Molecular dynamics within diorganotin systems: Solution and solid state studies of new mixed distannoxane dimers [tBu2(Cl)SnOSn(Cl)R2]2. Inorg. Chem., 36: 2023-2029.
    CrossRef  |  


  9. Holecek, J., M. Nadvornik, K. Handlir and A. Lycka, 1986. 13C and 119Sn NMR spectra of di-n-butyltin (IV) compounds. J. Organomet. Chem., 315: 299-308.
    CrossRef  |  


  10. Ibrahim, I.T., 2009. Preparation of 99mTc-metronidazole as a model for tumor imaging. J. Radioanal. Nuclear Chem., 281: 669-674.
    CrossRef  |  


  11. Kapoor, R., A. Gupta, P. Kapoor and P. Venugopalan, 2003. Synthesis and characterization of di-n-butyltin(IV) complexes with 4'/2'-nitrobiphenyl-2-carboxylic acids: X-ray crystal structures of [{(n-C4H9)2Sn(OCOC12H8NO2-4')}2O]2 and (n-C4H9)2Sn{OCOC12H8NO2-4'}2. Applied Organomet. Chem., 17: 600-606.
    CrossRef  |  Direct Link  |  


  12. Lawal, A. and J.A. Obaleye, 2007. Synthesis, characterization and antibacterial activity of aspirin and paracetamol-metal complexes. Biokemistri, 19: 9-15.
    Direct Link  |  


  13. Nath, M., S. Pokharia, G. Eng, X. Song and A. Kumar et al., 2004. New trimethyltin(IV) derivatives of dipeptides: Synthesis, characteristic spectral studies and biological activity. Applied Organomet. Chem., 18: 460-470.
    CrossRef  |  


  14. Nath, M., R. Yadav, G. Eng, T.T. Nguyen and A. Kumar, 1999. Characteristic spectral studies and antimicrobial and anti-inflammatory activities of diorganotin(IV) derivatives of dipeptides. J. Organomet. Chem., 577: 1-8.
    CrossRef  |  


  15. Nath, M., S. Pokharia, G. Eng, X. Song and A. Kumar, 2003. Comparative study of structure-activity relationship of di- and tri-organotin(IV) derivatives of amino acid and peptides. J. Organomet. Chem., 669: 109-123.
    CrossRef  |  


  16. Nath, M., S. Pokharia, G. Eng, X. Song and A. Kumar, 2006. New triorganotin (IV) derivatives of dipeptides as models for metal-protein interactions: Synthesis, structural characterization and biological studies. Spectrochim. Acta Part A: Mol. Biomol. Spectrosc., 63: 66-75.
    CrossRef  |  


  17. Puri, J.K., H. Kaur and A. Singla, 2008. Synthesis of macrocyclic compounds using tin templates. Main Group Met. Chem., 31: 243-252.
    CrossRef  |  


  18. Puri, J.K., G. Singh and P. Duggal, 2008. Synthesis, characterization and reactivity of a novel six-membered 1-isothiocyanato silatrane. Phosphorus Sulfur Silicon Related Elem., 183: 1853-1861.
    CrossRef  |  


  19. Puri, J.K., R. Singh, V. Kaur, G. Singh and R.P. Sharma, 2009. Synthesis and characterization of penta- and hexa-coordinated silicon compounds with schiff bases containing-NCS functionality. Main Group Met. Chem., 32: 79-84.
    CrossRef  |  


  20. Puri, J.K., R. Singh, V.K. Chahal, R.P. Sharma, J. Wagler and E. Kroke, 2011. New silatranes possessing urea functionality: Synthesis, characterization and their structural aspects. J. Organomet. Chem., 696: 1341-1348.
    CrossRef  |  


  21. Sagdinc, S. and S. Bayari, 2004. Spectroscopic studies on the interaction of ofloxacin with metals. J. Mol. Struct., 691: 107-113.
    CrossRef  |  


  22. Sandhu, G.K. and H. Kaur, 1990. Preparation and characterization of diphenyllead(IV) and triphenyllead(IV) complexes with N-protected amino-acids and the dipeptides. Applied Organomet. Chem., 4: 345-352.
    CrossRef  |  


  23. Stefano, R.D., M. Scopelliti, C. Pellerito, T. Flore and R. Vitturi et al., 2002. Organometallic complexes with biological molecules: XVII. Triorganotin(IV) complexes with amoxicillin and ampicillin. J. Inorg. Biochem., 89: 279-292.
    CrossRef  |  


  24. Sun, R.W.Y., D.L. Ma, E.L.M. Wong and C.M. Che, 2007. Some uses of transition metal complexes as anti-cancer and anti-HIV agents. Dalton Trans., 43: 4884-4892.
    CrossRef  |  Direct Link  |  


  25. Theophanides, T., 1984. Metal ions in biological system. Int. J. Quantum Chem., 26: 933-941.
    CrossRef  |  Direct Link  |  


  26. Ukita, T., Y. Nakamura, A. Kubo, Y. Yamamoto, Y. Takahashi, J. Koetera and T. Ikeo, 1999. 1-arylnaphthalene lignan: A novel scaffold for type 5 phosphodiesterase inhibitor. J. Med. Chem., 42: 1293-1305.
    CrossRef  |  


  27. Nath, M., S. Pokharia, G. Eng, X. Song and A. Kumar, 2004. Diorganotin(IV) derivatives of dipeptides containing at least one essential amino acid residue: Synthesis, characteristic spectral data, cardiovascular and anti-inflammatory activities. Synth. React. Inorg. Met. Org. Chem., 34: 1689-1708.
    CrossRef  |  


©  2022 Science Alert. All Rights Reserved