Cytotoxic Steroidal Saponins from the Rhizomes of Tacca integrifolia

Three new steroid saponins (3 beta.25R)-spirost-5-en-3-y1 6-deoxy-alpha-L-mannopyranosyl-(1 -> 2)-[beta-D-glucopyranosyl-(1 -> 4)-6-deoxy-alpha-L-mannopyranosyl-(1 -> 3)-beta-D -glucopyranoside (1), (3 beta 22R,25R)-26-(beta-D-glucopyranosyloxy)- (1), (3 beta,22R,25R)- 22-hydroxyfurost-5-en-3-y16-deoxy-alpha-L-mannopyranosyl-(1 -> 2)-D-d-deoxya-L-mannopyranosyl-(1 3)]-/I-0-glucopyranoside (3), and (3fi,22R,25R)-260-1.)-glucopyranosyloxy)22-hydroxyfurost-5-en-3-y1 6-deoxy-alpha-L-mannopyranosyl-(1 -> 2)-beta-D-glucopyranosyl-(1 -> 4)-6-deoxya-L-mannopyranosyl-(1,3)1-fi-0-glucopyranoside (5), as well as the new pregnane glycoside (3 beta,16 beta)3-([6-deoxy-alpha-L-mannopyranosyl-(1 2)[6-deoxy-a-L-mannopyranosyl-(1 3)]-fi-u-glucopyranosyl Joxy1-20-oxopregn-5-en-16-y1 (4R)-5-(/3-0-glucopyranosyloxy)-4-methylpentanoate (6), were isolated from the rhizomes of Tacca integrifolia together with two known (25R) configurated steroid saponins (3)6,25R)-spirost-5-en-3-y1 6-deoxy-a-L-mannopyranosyl-(1 2)f6-deoxy-a-L-mannopyranosyl-(1 3)]-13-0-glucopyranoside (2) and (3/3,22R,25R)-260-0-glucopyranosyloxy)-22-methoxyfurost-5-en-3-y1 6-deoxy-a-L-mannopyranosyl-(1 > 2)46-deoxy-a-L-mannopyranosyl-(1 3) I-S-0-glucopyranoside (4). The cytotoxic activity of the isolated compounds was evaluated in HeLa cells and showed the highest cytotoxicity value for compound 2 with an /C50 of 1.2 0.4 1.tm. Intriguingly, while compounds 1-5 exhibited similar cytotoxic properties between 1.2 0.4 (2) and 4.0 0.6 1.1m (5), only compound 2 showed a significant microtubule-stabilizing activity in vitro.