Improving the anticancer activity of fluorinated glucosamine and galactosamine analogs by attachment of a ferrocene or ruthenium tetrazene motif

Acylated N-acetyl hexosamine hemiacetals are known for their cytotoxicity. We have previously reported that cytotoxicity can be increased by replacing one or more acyloxy groups with fluorine. Herein, we present the synthesis of 4,6-difluorinated d-gluco- and 4-fluorinated d-galacto-configured hexosamine-derived glycoconjugates with organoruthenium or ferrocene complexes and their in vitro cytotoxicity against three cancer cell lines (A2780, SK-OV-3, and MDA-MB-231) and one noncancerous cell line (HEK-293). The attachment of the organometallic moiety at the 2-position significantly enhanced the cytotoxicity, especially against triple-negative MDA-MB-231 and the cisplatin resistant SK-OV-3 cancer cells. We observed a clear significance of an unprotected and acetyl protected anomeric hydroxyl for the cytotoxicity. Glycoconjugates with a non-hydrolysable organic or organometallic group at the anomeric position were generally nontoxic. A more detailed analysis revealed that, in particular, complexes with the ruthenium tetrazene complex induced apoptosis in both SK-OV-3 and MDA-MB-231 cells, as demonstrated by western blot analysis and Annexin V-FITC/PI staining. The structures of the two most cytotoxic organoruthenium and ferrocene glycoconjugates were confirmed by X-ray diffraction analysis. Attachment of ruthenium tetrazene or ferrocenyl-triazole substituents at the 2-position of cytotoxic fluorinated glucosamine hemiacetals increased the sugar cytotoxicity by one order of magnitude via induction of apoptosis. The presence of a hydroxyl or beta-acetate at the anomeric position is essential for cytotoxicity. image