Chem. Pharm. Bull. 55(11) 1649—1651 (2007)

ingolipids (GSLs) from echinoderms, a series of studies on the isolation and structural elucidation of biologically active GSLs have been performed in our laboratory. In the study of the GSLs of the crinoidea, we reported on the isolation and structural elucidation of cerebrosides, inositolphosphoceramide, and the glycosyl inositolphosphoceramide-type gangliosides from the feather star Comanthus japonica. Continuing the preceding studies, isolation and characterization of GSLs from the feather star Comanthina schlegeli (Hanaumishida in Japanese) was conducted. In this paper, we report on the isolation and structure of a new and a known glycosyl inositolphosphoceramide-type ganglioside from the whole bodies of C. schlegeli. The polar lipid fraction, which was obtained from the chloroform/methanol extract of the whole bodies of C. schlegeli, was subjected to repeated column chromatography followed by preparative thin-layer chromatography (TLC) to give two polar compounds, 1 and 2, each showing a single spot on silica gel TLC. Compounds 1 and 2 show strong hydroxy, amide and phosphate absorptions in the IR spectrum and exhibit a positive reaction to the Dittmer–Lester reagent, which indicates the presence of a phosphate group. The negative-ion FABMS of 1 and 2 exhibits quasimolecular ion peaks [M H] at m/z 1139, 1167 in 1 and 1155, 1183 in 2 together with fragment ion peaks at m/z 834, 862 and 672, 700 in both 1 and 2 as shown in Fig. 2. The loss of 305 and 321 mass units from the molecular ions suggested the existence of a monomethylated N-acetyland N-glycolyl-neuraminic acid residues in 1 and 2, respectively. Furthermore, 1 and 2 were hydrolyzed with 5% acetic acid to yield L-myo-inositol-1-O-phosphoceramide (3) which was previously reported. Therefore 1 and 2 are suggested to be monomethylated N-acetyland N-glycolyl-neuraminosyl inositolphosphoceramide (Fig. 1). The structure of the ceramide moiety of 1 and 2 was verified as follows. When 1 and 2 were subjected to mild alkaline hydrolysis with 1 M KOH, the ceramide part (4) was obtained with sugar part (5). Compound 4 was methanolyzed with methanolic hydrochloric acid, and a mixture of fatty acid methyl esters (FAM) and a long-chain base (LCB) was obtained. The FAM mixture was analyzed using GC-MS, which revealed the presence of C22:0 and C24:0 normal fatty acids as the major components. On the other hand, the LCB was characterized as C16-sphingosine, based on GC-MS analysis of its TMS derivative. The stereochemistry of 4 must be (2S,3R,4E), since the H-NMR spectrum and the optical rotation of 4 ( 5.9) were in good agreement with that of the ceramide ( 5.8) obtained from the gorgonian Acabaria undulata which has the 2S, 3R, 4E configuration. The structures of the sugar part of 1 and 2 were established as follows. Compound 1 and 2, respectively, was methylated with CD3I according to the Hakomori method 10) and yielded the perdeuteriomethylated product 6 and 7. Upon methanolysis followed by acetylation of 6 and 7, respectively, the partially trideuteriomethylated sialic acid derivatives (S-1 and S-2) originated from the terminal 9-O-Me-NeuAc and the terminal 9-O-Me-NeuGc were detected in GC-MS analysis, which indicated the presence of terminal 9-O-Me-NeuAc and NeuGc moiety in 1 and 2. The linkage site of the 9-O-Me sialic acid moiety to the myo-inositol portion was elucidated by methylation linkage analysis combined with ammonolysis. Compound 8, the permethylated 1 and 2, was hydrolyzed with aqueous NH3 to give the partially methylated inositol derivative, S-3. S-3 was identified as 2,4,5,6-tetramethylated myo-inositol by comparison of EI-MS spectrum of its TMS derivative with that of the myo-inositol derivative. Consequently, the sialic acid residues in 1 and 2 must be linked at the C3-OH group of the inositol part, as shown in Fig. 1. The configurations of the sialic acids are believed to be a on the basis of their H-3eq signals (d 2.73 ppm) in the HNMR spectrum of 5. In general NeuAc and NeuGc are thought to be D-series, then 1 and 2 are 9-O-methyl-(N-acetyl-a-D-neuraminosyl)(2→3)-inositolphosphoceramide and 9-O-methyl-(N-glycolyl-a -D-neuraminosyl)-(2→3)-inositolphosphoceramide, which contain C16-sphingosine and C22:0, C24:0 fatty acids as Constituents of Crinoidea. 5. Isolation and Structure of a New Glycosyl Inositolphosphoceramide-Type Ganglioside from the Feather Star Comanthina schlegeli