Synthesis, structure, and in vitro antiproliferative activity of cyclic hypervalent organobismuth(III) chlorides and their triphenylgermylpropionate derivatives

Six compounds of cyclic hypervalent organobismuth(III) chlorides and triphenylgermylpropionates bearing a nitrogen or sulfur atom as intramolecular coordination atom have been synthesized and characterized. The results of single-crystal X-ray analysis reveal that the eight-membered tetrahydroazabismocine rings are highly flexible. The Bi–S or Bi–N bond lengths in the thiabismocine or azabismocine derivatives are dependent on how the substituted groups are acting on the Bi, S or N atom. The replacement of the chlorine atom in azabismocine and thiabismocine with the triphenylgermylpropionic group (Ph3GeCH2CH2COOsingle bond) leads to the lengthening of Bi–N and Bi–S bond. The substituents connected with the nitrogen atom also have an effect on the Bi–N bond length of azabismocine. For example, a cyclohexyl group has electron-donating ability higher than a phenyl group; the replacement of the former by the latter would lead to the decline of Bi–N bond length and increase of CAr–Bi–CAr angle in the eight-membered ring. The in vitro antiproliferative activities of the fabricated materials were compared on gastric carcinoma cells by means of the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide (MTT) method. It was found that the compounds show antiproliferative activity on gastric carcinoma cells (MGC-803) much higher than that of cisplatin. Moreover, there is enhancement of antiproliferative activity when the chlorine atom of the bismocine compounds is replaced by the triphenylgermylpropionic group, giving a low IC50 value of 0.7 μM for thiabismocine triphenylgermylpropionate.