In situ C-C bond cleavage of vicinal diol following by the lactolisation resulted from separated treatment of Arjunolic acid (1), 24-hydroxytormentic acid (2) and 3-O-β-D-glucopyranosylsitosterol (3) with sodium periodate and silica gel in dried THF according to the strategic position of hydroxyl functions in the molecule. The reaction led to a lactol pentacyclic triterpenes 1A, 2A and a bicyclotriacetal of β-sitosterol 3A. These products were further acetylated and the cytotoxicity of all molecules was evaluated against human fibrosarcoma HT1080 cancer cells lines.