Other Therapeutic Potential of Organotin Compounds

From the foregoing, it is plain that considerable effort has been devoted to investigating the anti-tumour potential of organotin compounds. However, by no means is the study of therapeutic potential of organotin compounds restricted to cancer diseases. In the following paragraphs, a brief overview of recent studies investigating the potential activity of organotin compounds against other diseases is given.

Following the screening for anti-tumour potential, many studies have coupled various carboxylate ligands to organotin centres and subjected the products to anti-bacterial trials.97 100 In addition, studies on other species such as barbiturates101 and thiones102 have also been conducted. The principle of complexing pharmaceutically active substrates to organotin and investigating the resultant activity is one motivation for these trials. Thus, a series of tri-n-butyltin carboxylates, where the ligands have anti-inflammatory and analgesic properties, were prepared and of these, the smallest carboxylate of the series, i.e. derived from 3-furan-2-yl-acrylic acid anion, Figure 22.5(a), was the most active and had higher activity than the reference drugs Ampicillin® and Cephalexin® in most of the bacteria investigated.97 A similar strategy was applied recently where tricyclohexyltin carboxylates derived from triorgano-germyl propanoic acids (see Chapter 15 on therapeutic germanium compounds) were investigated.98 Generally, the new compounds had little anti-bacterial activity. One of the compounds, i.e. (C6H11)3SnO2CH2CH(Ph)Ge(o-tolyl)3, displayed significant activity against a Trichophyton species, a human pathogen that is responsible for hair, nail and skin infections and, importantly, greater activity than the reference drug Imipenem®.

Figure 22.4 A boron-based triphenylstannate, sodium bis[2-(3',6',9'-trioxadecyl)-1,2-dicarba-closo-dodecaborane-1-carboxylato]triphenylstannate, Na[(CH3OCH2CH2OCH2 CH2OCH2CH2)-1,2-C2B10H10-9-COO)2SnPh3], formed unexpectedly during the synthesis of the type 3 analogue83

Figure 22.4 A boron-based triphenylstannate, sodium bis[2-(3',6',9'-trioxadecyl)-1,2-dicarba-closo-dodecaborane-1-carboxylato]triphenylstannate, Na[(CH3OCH2CH2OCH2 CH2OCH2CH2)-1,2-C2B10H10-9-COO)2SnPh3], formed unexpectedly during the synthesis of the type 3 analogue83

CO2H

CO2H

Figure 22.5 Chemical structures of (a) 3-furan-2-yl-acrylic acid and (b) 2-mercapto-3-phenyl-acrylic acid

CO2H

The anti-microbial activity of a series of triphenyltin sulfanylpropenoates has been reported recently99 (see Figure 22.5b for a chemical structure of a representative ligand). The essential role that tin plays in therapeutic potential was demonstrated in this study, in that the free ligands displayed no anti-bacterial activity but their anionic triphenyltin complexes did. Also noteworthy is the observation that the organotin compounds were more potent against Grampositive bacteria.99 This was correlated with the difficulty of the organotin species to penetrate the outer membrane of Gram-negative bacteria.

Organotin compounds have also been investigated for anti-trypanocidal activity.103 Human sleeping sickness is a major health problem in parts of Africa and new drugs are required to overcome drug resistance developed by trypanosome strains. A series of water-soluble diorganotin thiolates, of the general formula (CH3OCH2CH2OCH2CH2CH2)2Sn(SR)2, i.e. containing a tin-bound water-solubilizing group were investigated for anti-trypanocidal activity, both in vitro and in vivo.103 The organotin compounds investigated did not possess significant promise in this context although it was noted that the organotin compounds were well tolerated by the animals tested.103

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