Organotin(IV) complexes of ethylsarcosine hydrochloride: Synthesis, characterization and in vitro cytotoxic activity

The synthesis and characterization of new coordination compounds of some organotin(IV) chlorides with ethylsarcosine hydrochloride (N-methylglycine ethyl ester hydrochloride) is reported; the ligand molecules appear to be bound to the tin atoms through the carbonyl oxygen atoms by means of dative bonds. As single crystals were not obtained, a number of experimental techniques were used to accomplish a definitive characterization and determination of their structure. The results obtained by ¹H, ¹³C, ¹¹⁹Sn NMR, FT-IR and ^119mSn Mössbauer spectroscopy and thermogravimetric analysis suggested pentacoordination for the 1:1 (Sn:ligand (ESH)) derivatives, [R₂SnCl₂(ESH)]⁺Cl^-, in a trigonal bipyramidal (TBP) structure, and hexacoordination for the 1:2 complexes, [R₂SnCl₂(ESH)₂]²⁺2Cl^-, in an octahedral structure (R = Me, n-Bu, Ph; ESH = protonated ethylsarcosine, CH₃CH₂O(O)CCH₂N (CH₃)H₂⁺). The triphenyltin(IV) chloride ethylsarcosine hydrochloride derivative exists only as a 1:1 pentacoordinated adduct in a strongly distorted TBP structure. Finally, the compounds have been tested for in vitro cytotoxic activity against human adenocarcinoma HeLa cells, showing, in some cases, a high potency, even at low concentration.