ORGANOTIN(IV) CARBOXYLATES: POTENTIAL ANTI-TUMOR AND ANTI-INFLAMMATORY AGENTS

Abstract

Organornetallic chemistry is the study of chemical compounds containing carbon - metal bonds. Today organometallic chemistry has reached a noticeable position due to its tremendous contribution in pharmaceutical, semiconductors, catalysis, agricultural, and other technological applications. Among them one of the fastest growing lelds is bioorganometallic chemistry. Research in bioorganornetallic medicinal chemistry focuses on designing new types of drug molecules by utilizing various techniques such as combinatorial chemistry, computer-aided molecular design and new types of highly sophisticated receptor-based and cell biological assays for drug activity. lhc large amount of novel functions, new structures and various properties lead to the phenomenal success of transition—metal organometallic chemistry (TMOC). Along with organotransition complexes, the spectacular progress has also been made in organometallic compounds of main group elements such as aluminum, boron, lead, lithium, silicon and tin. Organotin complexes exhibit structural diversity which contributes to various applications. Organotin(IV) compounds have been found useful in several industrial and commercial applications such as agricultural biocides, disinfectants. anti-fouling agents, wood preservatives, stabilizers for poly(vinyl chloride), flame retardants, smoke suppressants, anti-wear agents, hornogenous catalysts, recycling agents and curing agents for room temperature "vulcanization" of' silicones. Organotin(IV) complexes have also been used as versatile synthetic reagents for various organic transformations and as catalyst for the production of polyoretlianes. A number of organotin(lV) compounds have found to be toxic, and there is increasing concern regarding their widespread use in environmental and Ar biological systems. During the last few decades, organotins have emerged as potential biologically active compounds exhibiting antimicrobial, antiviral, antiherpes, antituberclosis, anti-inflammatory, anti-tumor and antihypertensive activities. Their signilicance from chemotherapeutic point of view has been enhanced further, because of their interactions with some clinically recommended drugs. Furthermore, it has been revealed that the biological activity of organotin compounds may be due to the transportation of R1Sn (n = 2 or 3) moieties formed by dissociation of easily hydrolysable groups attached to tin atom or organotin(W) compounds as one entity across the cell, and hence formulate the structure-activity correlation. It has been found that organotin compounds exhibit potential anti-tumor activity. Among organotin compounds, organotin carboxylates are very important. Organotin(IV) carboxylates contain 11 Sn -o bond formed through 000 group and therefore, exhibit a number of interesting structural features which enable them to exhibit anti-tumor activity. Anti-tumour activity and mode of action of -- organotin carboxylates have been studied and reported in the literature, however literature does not reveals the exact mechanism for their activity. Though several organotin(IV) carboxylates have been reported but there is lack of information about coordination behaviour of simple carboxylic acids of plant/animal origin which are biologically important, and the structural features of corresponding organotin carboxylates have not been studied in detail. Several organotin(IV) carboxylates with antiviral. antibacterial and antifungal activity have been studied, but little work on in vitro anti-cancer activity of the organotin(IV) carboxylates has been reported. Moreover, the mode of action of simple organotin halides has been studied extensively. 1-lowever, few studies explaining the mechanism for anti-tumor activity of organotin(IV) carboxylates has been reported. The motive of the present work is to view insight the pathway of anti-tumor activity of the organotin(IV) carboxylates via various assays: enzyme assays. DNA fragmentation, acridine orange and cornet assay. Anti-tumor activity and anti-inflammatory activity are related to each other. Every deadly disease is associated with pain or inflammation, therefore, an anti-tumor drug with anti-inflammatory properties is desirable, in light of this anti-inflammatory and acute toxicity studies have also been performed. Microwave-assisted method for the synthesis of organotin complexes has emerged as quick. environment friendl, Cost effective and energy efficient. Very few examples are known in literature for the synthesis of organotin(IV) carboxylates via microwave-assisted method. Hence the drive \\as to synthesize the organotin(IV) carboxylates via new microwave-aided methodology and as well as via conventional thermal method, and compare the two methods completely through physical data, analytical measurements and spectroscopic studies. Keeping in view the wide range of applications of the organotin(IV) compounds and the biological importance of simple carboxylic acids of planllanimal origin, it was considered to synthesize oragnotin(IV) derivatives of carboxylic acids viz. lauric acid, myristic acid, stearic acid, orotic acid, hippuric acid, glucuronic acid, mandelic acid and gallic acid, and investigate their structural and biological aspects. An attempt has been made to compile the work to obtain a better insight into the coordination behaviour of organotin(IV) moieties with carboxylic acids along with their anti-tumor activity, their mode of action for cytotoxicty and anti-inflammatory activity. In order to maintain the clarity of the presentation. the work embodied in the thesis is systematically divided into the following chapters. - First chapter presents the general introduction and an overvicv of some important applications of organotin(IV) compounds. A critical and comprehensive review of the available literature on the organotin(IV) carboxylates with special reference to their synthetic procedures. structural characterization, their anti-tumor activity and mode of action has also been presented. Second chapter incorporates the details of make, purity and other specifications of the materials used in the present study. The specifications of the instruments used for spectroscopic studies (FTJR, NMR and ESI-MS) and the details of the procedures used therein have been included. The methodology used for the biological studies (anti-tumor activity, enzyme assays. DNA-fragmentation, acridinc orange, comet assay, anti-inflammatory and toxicity studies of the synthesized complexes) has also been presented. The results obtained from these studies have been compiled and discussed in Chapters 3, 4, 5 and 6. Third chapter includes the synthesis and characterization of tn- and diorganotin complexes of the general formula RSn(L), [n = 3, in = I. R Me, n-Pr, n-Bu and Ph n = 2, m 2, R = Me, ii- Bu and n-Oct: L anion of laurie acid (lILA). stearic acid (HSA) and myristic acid (lIMA)I have been synthesized. The synthesized complexes have been characterized by elemental analysis, 1k. 'H. '3C. ''9Sn NMR and ESI-MS spectral studies. Triorganotin(IV) carboxylates and diorganotin(IV) carboxylates adopt trigonal bipyramidal and octahedral geometry around tin atom, respectively. The complexes have been screened in vitro for anti-tumor activity against five human cell lines i'i:. MCF-7 (mammary), 14EK-293 (kidney). PC-3 (prostate). lICT-15 (colon) and I lepG-2 (liver). Enzyme assays viz, lipid peroxidase, glutathione peroxidase, glutathione reductase and total glutathione assay have also been carried out to explore the cause of cytotoxiciy. The results of the enzymes assay indicate that ROS generation may be responsible for cytotoxicity but elevation in (lactate dehydrogenase) LDH suggests that necrosis cannot be excluded. Further, DNA ftagmentation, acridine orange and comet assay support the apoptosis as main cause of cytotoxicity of organotin(IV) carboxylates whereas the necrosis plays a minor role. The anti-inflammatory activity evaluation shows that the complexes possess moderate activity. Acute toxicity of the complexes has also been discussed in the chapter. Fourth chapter of' the thesis deals with the synthesis of triorganotin(lV) orotates [R3Sn(H,0r). R = Me, n-Bu and Ph], diorganotin(IV) orotates [R2Sn(H20r)2. R = Me, n-13u, n-Oct and Ph] and n-Bu2Sn(l-l0r) [FLOr = monoanion. l-10r2 = dianion of orotic acid (1 1Or) j. On the basis of various spectroscopic studies it is revealed that R3Sn(1 120r) and R7Sn(l 120r)2 exhibit distorted trigonal bi pyramidal and distorted octahedral geometry. respectively, and n-BwSn(HOr) iv shows both live-and six-coordination geometry around tin, in vitro anti-tumor screening against MCF-7. HEK-293, PC-3, HCT-15 and HepG-2 cell lines suggest that the n-Oct2Sn(1-I20r)2 is the most active complex among all of the studied complexes. DNA fragmentation and anti-oxidant enzyme assays on MCF-7 and PC-3 cell lines suggest that cytotoxic effect of the complexes is selectively mediated through the induction of apoptosis. The results obtained for the anti-inflammatory and toxicity of the synthesized triorganotin(IV) derivatives are also discussed. Fifth chapter enumerates the synthesis and characterization of triorganotin(lV) derivatives ci' hydroxy acids of general formula, R3Sn(L) [R = Me, n-13u and Ph; 1. = anion of glucuronic (I IC ILL). gallic (HGal) and mandelic (I-lMal) acid]. The complexes R-Sn(L) exhibit trigonal bipyramidal geometry which is well supported by elemental analysis, IR, 'II, 3C, ''9Sn NMR and ESI-MS spectral data. l'hesc organotin(IV) carboxylates have been screened in vitro against five cancer cell lines of - human origin viz. MCF-7, HEK-293, PC-3, I ICT- l 5 and HepG-2. These complexes are found to be cytotoxic to mildly cytotoxic in nature, and exhibited activity in the range 4-30 .tg/rnl.. Enzyme assays like, glutathione reductase, glutathione peroxidase, total glutathione content and lipid peroxidase assay on MCF-7 cells have also been performed. The results indicate that the reactive oxygen species generated in the cancer cells by the organotin(IV) carboxylates is responsible for cell death. Marginal increase of lactate dehydrogenase suggests that necrosis is also occurring to a small extent. DNA fragmentation assay, acridine orange assay and comet assay clearly support that the cell death is mainly due to apoptosis. The results obtained for the in vivo anti-inflammatory activity (% inhibition) and toxicity (LD50 in mg/kg) of the synthesized derivatives have been compiled and discussed in this chapter. Sixth chapter of the thesis incorporates microwave assisted reaction between triorganolin chlorides or diorganotin chlorides/oxides and hippuric acid (liHA), in 1:1 or 1:2 molar ratio which resulted in the formation of R3Sn(HA) (R = Ph, n-E3u. and Me) and RSn(l-IA)2 (R = n-Oct, n-Bu and Me) [HA = anion ot'hippuric acid], respectively. llowcvcr, complexes were also synthesized through conventional thermal conditions for comparison. The chapter contains complete comparison between the conventional thermal method (time taking, energy and solvent consuming) and microwave assisted method (cost effective, swift, environmental friendly and simple) on the basis of yield, time taken for synthesis and solvent consumed, physical characteristics, elemental analysis, IR. NMR and ESI-MS spectroscopic studies. In vitro anti-tumor screening, anti-inflammatory activity and acute toxicity of the complexes have also been discussed in this chapter.