Cynotofuranoside A-C: Uncommon C21-steroidal furanosides derived from the acid hydrolysate of Cynanchum otophyllum roots

Cynotofuranoside A-C (1–3), three previously undescribed C21-steroidal furanosides were isolated from the acid hydrolysate of Cynanchum otophyllum roots. Their structures were elucidated by extensive spectroscopic analysis including UV, IR, 1D and 2D NMR and HR-ESI-MS. Compounds 1–3 represented the first examples of 2,6-dideoxy-aldohexose in the form of furan ring attaching to 3β-OH of natural occurring C21-steroidal aglycones. The cytotoxicity of these compounds against human cancer MCF-7, HCT-116, HeLa, and HepG2 cells were evaluated. Compounds 1 and 3 showed moderate cytotoxic activities against HepG2 cancer cells with IC50 values of 43.15 and 34.36 μM, respectively.