Organotin(IV) Derivatives of L-Cysteine and their in vitro Anti-Tumor Properties

Organotin(IV) Derivatives of L-Cysteine and their in vitro Anti-Tumor Properties. Christos T. Chasapis a, Sotiris K. Hadj"kakou,a* Achilles Garoufis a, Nick Hadjiliads, Thomas Bakasb, Maciej Kubicki c, and Yang Mingd a* alnorganic and Analytical Chemistry, Department of Chemistry, University of loannina, 45110 Ioannina, Greece; bphysics of Material Laboratory, Department of Physics, University of loannina, 45110 Ioannina, Greece. Department of Chemistry, A. Mickiewicz, University, ul. Grunwaldzka 6, 60- 780 Poznan, Poland.. National Research Laboratory of Natural and Biomimetic Drugs, Peking University, Beij’ing 100083, Beijing, P. R. China. ABSTRACT The synthesis and characterization of the organotin compounds [(n-C4H9)zSn(cys)] (1), [(C6Hs)2Sn(cys)] (2), [(C6Hs)3Sn(Hcys)’(H20)] (3), {[(CH3)2Sn(Kcys)2]’2(H20)} (4), {[(n-C4Hg)zSn(Kcys)z]’2(H20)} (5) and {[(C6Hs)zSn(Kcys)z].2(H20)} (6) (where H_cys L-cysteine) are reported. The compounds have been characterized by elemental analysis and 1H-NMR, Uv-Vis, FT-IR and MOssbauer spectroscopic techniques. Attempted recrystallization of (2) in DMSO/methanol 2:1 solution yielded after several days unexpectedly the dimeric compound bis(tri-phenyltin)sulphide {[(C6Hs)aSn]2S} (7) which has been characterized by x-ray analysis. The structure of the parent complex (2) as well as the mechanism of the decomposition of cysteine are being further investigated. The in vitro anticancer activity of complexes (I)- (6), against human leukemia (HL60), human liver (Bel7402), human stomach (BGC823) and human cervix epithelial human carcinoma (Hela), nasopharyngeal carcinoma (KB) and lung cancer (PG) tumor cells, were evaluated. Keywords: Bioinorganic chemistry, organotin(IV) compounds, mercapto amino acids, L-cysteine, antitumour compounds *All correspondence should be addressed to: Assistant Professor S.K. Hadjikakou; e-mail: ; tel. +30-26510-98374 Professor N. Hadjiliadis: e-mail: , tel. +30-26510-98420; fax +30-26510-44831 43 Vol. 2, Nos. 1-2, 2004 Organotin (IV) Derivatives of L-Cysteine and their in vitro Antitumor Properties I. INTRODUCTION The biological activity of organotin(IV) compounds is well known/1-3/. Most organotin(IV) compounds are generally toxic /3/. The binding of organotins by thiol groups, on the other hand, is significant in biological systems /4/. A great deal of work has been reported thus far, on the interaction of organotin compounds with thiol-containing mercapto-amino acids such as cysteine and its derivatives/3, 5-14/. The interpretation of the results however, was rather controversial. Thus, based on M6ssbauer spectroscopy Barbieri et al. /6/proposed a penta-coordinate structure for the L-cysteinato(S-)-triorgano-tin(IV) hydrate [R3Sn(Cys)(H20)] (R Me- or Et- group) /6, 8/. A penta-coordinate geometry around tin atom was also proposed by Huger et al./10/for [Ph2Sn(Cys)]. The anti-leukemic activity of compound [Ph2Sn(Cys)] was evaluated by Huber et al./8/and was found to be remarkable in relation to its low toxicity. A tetrahedral arrangement around tin(IV) was proposed for [Ph3Sn(HCys)] by Hyams et al. /14/and Huger et al. /10/. According to spectroscopic data Bamgboye et al. /7/ proposed a polymeric chain structure for [(Ph3Sn)2cys] with penta-coordinated tin atom/7/, while a double anionic structure was proposed by Domazetis et al./13/ for the {[(Me)2Sn(OH)2(cys)] 2} at high pH. The crystal structure of the ethyI-L-cyteinatoS,N-(chlorodimethyl) stannate(IV) [(Me)2Sn(CI)(SCH2CH(NH2) COOC2H5] /11/ was determined by X-ray analysis and indicated S, N chelated coordination of the ethyl-ester of cysteine with the tin atom in a distorted trigonal bibyramidal configuration. Another demand for such studies raised from the potential pharmaceutical application of organotin compounds/5, 15/. Today, a number of organotin (IV) derivatives are known to have an efficient anti-turnout activity/15/. A comparison of the structures of the active and inactive compounds suggests that all active compounds should conform to the following requirements: (i) to have available coordination positions around Sn, (ii) to have a relatively stable ligand-Sn bond (e.g. Sn-N and Sn-S) with low hydrolytic decomposition/5/. The aim of the present work is the exploration of new synthetic routes for the synthesis of organotin(IV) complexes with cysteine, the better characterization of the compounds formed and the evaluation of anticancer activity of the complexes derived and characterized. 2. EXPERIMENTAL Materials and Instruments: All solvents used were reagent grade, while organotin chlorides (Aldrich), cysteine (Merck) were used with no further purification. Elemental analysis for C, H, N, and S were carried out with a Carlo Erba EA Model 1108. Infra-red spectra in the region of 4000-370 cm were obtained in KBr discs while far-infra-red spectra in the region of 400-50 cm were obtained in polyethylene discs, with a Perkin-EImer Spectrum GX FT-IR spectrometer. A Jasco Uv/Vis/NIR V 570 series spectrophotometer was used to obtain the electronic absorption spectra.. The H-NMR spectra were recorded on a Bruker AC250 MHFT-NMR instrument in CDCI. solutions. Chemical shifts i are given in ppm using TMS as an internal reference. The gsn 44 Christos 7". Chasapis. et al. Bioinorganic Chemistry and Applications MCssbauer spectra were collected at various sample temperatures, with a constant acceleration spectrometer equipped with CaSnO3 source kept at room temperature. Synthesis of L-cysteinato-k2S, O-di-n-butyl-tin(IV), [(n-C4H9) 2Sn(cys)]} (I) Cysteine (H2cys) (0.121 g, 1.0 mmol) was treated with Na2CO3 (0.106 g, 1.0 mmo|) Na2CO in H20 (17 cm ) followed by addition of a solution of di-butyltin(IV) dichloride [(n-CaH9)2SnCI2] (0.152 g, 0.5 mmo|) in methanol (3 cm). Chloroform (20 cm ) was then added to this solution and the resulting mixture was stirred for 3 h. The organic layer was dried over Na2SO4 and filtered to yield a clear solution. Removal of solvent yielded a white powder of compound (1). Yield 0.045 g (26%); m.p.- 208-210 C;. Elemental analysis, found: C: 37.63; H: 6.76; N: 3.57, S: 8.96 %, calculated for CHz3NOzSSn: C: 37.53; H: 6.58; N: 3.98, S: 9.11%. IR (cml): 3240s, 2956vs, 2923vs, 2855s, 1641vs, 1545m, 1464m, 1429m, 1390s, 1322s, 1300, 1050m, 867m, 800w, 681m, 583m; 460s, 397m. Synthesis of L-cysteinato-k2S, O-diphenyl-tin(IV), [(C6Hs) 2Sn(cys)]} (2): Cysteine (H2cys) (0.243 g, 2 mmol) was treated with NazCO (0.212 g, 2 mmol) in H20 (17 cm ) followed by addition of a solution of di-pheny|tin(IV) dichloride [(C6Hs)2SnCI2] (0.344 g, mmol) in methanol (3 cm). A white precipitate of (2) was formed immediately. Yield 0.08 g (20 %); m.p. 240-245 C;. Elemental analysis, found: C: 45.86; H: 3.89; N: 3.62, S: 8.35 %, calculated for CsHINO2SSn: C: 45.96; H: 3.85; N: 3.57, S: 8.18 %. IR (cm): 3240s, 2956vs, 2923vs, 2855s, 1641vs, 1545m, 1464m, 1429m, 1390s, 1322s, 1300m, 1050m, 867m, 800w, 681 m, 583m; 460s, 396m. Attempted re-crysta (...truncated)