Astasin, a novel cytotoxic carbohydrate-conjugated ergosterol from the colorless euglenoid, Astasia longa

A novel cytotoxic carbohydrate-conjugated ergosterol (astasin) was found in cells of the colorless euglenoid, Astasia longa. Astasin accounted for about 2.4% of the total lipid of the cells. FAB-MS spectra of astasin showed MH+, 583.3387 (M+, C35H50O7). Astasin was composed of ergosterol (1 eq.), alpha-D-xylopyranose (1 eq.), and oxalic acid (1 eq.). By the acetylation using acetic anhydride and pyridine, oxalic acid was removed from astasin, and three hydroxyl groups of the xylopyranose moiety were acetylated. The two dimensional 13C- and 1H-NMR spectra suggest the oxalic acid was esterified with hydroxyl groups at C-2 and C-3 of the xylopyranose moiety and the hydroxyl group at C-1 of the xylopyranose was glycosidically linked to the hydroxyl group at C-3' of the ergosterol moiety. From the results, the structure of astasin was identified as 2,3-oxalyl-alpha-D-xylopyranosyl (1 --> 3')ergosterol. When cells of HL 60, a human lymphoma, were cultured with astasin, 50% of the cell growth was inhibited at 5.0 micrograms astasin/ml medium, and the cell growth was inhibited completely and 50% of the initial cells was killed at 10.0 micrograms astasin/ml medium.