Asterosaponin Ophidianoside F from Gonads of the Far-Eastern Starfish Aphelasterias japonica

Abstract

Physiologically active steroidal oligoglycosides from starfish (asterosaponins) are known to fulfill protective functions and regulate maturation processes of ova in these animals [1, 2]. In continuation of research on polar steroidal compounds from the Far-Eastern starfish Aphelasterias japonica [3], we studied the asterosaponin fraction from gonads of animals collected in Pos1et bay of the Sea of Japan in July 2002 at a depth of 10 m. Gonads from A. japonica were extracted with ethanol (70%). The aqueous alcohol solution was washed with benzene to remove nonpolar lipids and concentrated in vacuum. Column chromatography of the resulting dry solid over Amberlite XAD-2, Sephadex LH-20 (ethanol:water, 2:1), and silica gel (CHCl3:C2H5OH, 1:1→1:10) and subsequent HPLC over Diasphere-110-C18 (5 μm, 4×250 mm, CH3OH, 60%) isolated a pure steroidal glycoside (3 mg, 0.067% yield per dry weight of the aqueous ethanol extract). 1H and 13C NMR spectra and MALDI/TOF and LSI mass spectra established that the isolated compound was asterosaponin and had the steroidal aglycon thornasterol A and an oligosaccharide chain of five monosaccharide units including two quinovose, two xylose, and one fructose unit. Acid hydrolysis of this glycoside gave total monosaccharides that were identified as D-quinvose, D-xylose, and D-fucose (2:2:1) (TLC, GC of polyol peracetates, specific rotation). Signals of protons and C atoms in NMR spectra of the glycoside agreed completely with the corresponding signals of ophidianoside F from the starfish Ophidiaster ophidianus [4]. The sequence of monosaccharides in the isolated compound was also confirmed by the fragmentation in LSI mass spectra. We concluded from this that the isolated glycoside was identical to ophidianoside F and had the structure (20R)-6α-O-{β-D-fucopyranosyl-(1→2)-β-D-xylopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-Dxylopyranosyl-(1→3)-β-D-quinovopyranosyl}-20-hydroxy-23-oxo-5α-cholest-9(11)-en-3β-yl sodium sulfate. This asterosaponin was found for the first time in the Far-Eastern starfish Aphelasterias japonica. Its MALDI/TOF and LSI mass spectra have not been previously reported. Ophidianoside F: amorphous compound, [α]D +0.5° (c 0.2, CH3OH); MALDI/TOF (+) mass spectrum (m/z): 1291 [MK + K] +, 1275 [MNa + K] +, 1259 [MNa + Na] +, 1139 [MNa + Na 120] +; MALDI/TOF (-) mass spectrum (m/z): 1212 [MNa Na] -, 1113 [MNa Na 100] -, 1067 [MNa Na 146] -; LSI (+) mass spectrum (m/z): 1253 [MK + H] +, 1237 [MNa + H] +, 1153 [MK + H 100] +, 1137 [MNa + H 100] +, 1107 [MK + H Fuc] +, 1091 [MNa + H Fuc] +, 975 [MK + H Fuc Xyl] +, 959 [MNa + H Fuc Xyl] +; LSI (-) mass spectrum (m/z): 1213 [MNa Na] -, 1113 [MNa Na 100] -, 1067 [MNa Na Fuc] -, 935 [MNa Na Fuc Xyl] -, 657 [MNa Na Fuc Xyl Xyl Quin] -, 511 [MNa Na Fuc Xyl Xyl (Quin) Quin] -, 411 [511 100]-. PMR (300 MHz, CD3OD) and 13C (75.5 MHz, C5D5N) spectra were identical to those published previously [4].