As part of our continuous search for bioactive metabolites from marine organisms, [2][3][4][5][6] we have investigated a soft coral species belonging to the genus Lobophytum collected from the Indian Ocean. Earlier studies of the genus Lobophytum led to the isolation of several sesquiterpenoids, cembrane and lobane diterpenes, sterols and sphingolipids. 7,8) Several compounds from this genus showed cytotoxic, [9][10][11] anti-HIV, 12) antibacterial, 13) and ichthyotoxic [14][15][16][17] activities. In this paper we report the isolation and structural elucidation of three new sphingolipids and a sterol along with cytotoxic activity of a known sphingolipid isolated from the organism.Sphingolipids exist widely in the eukaryotic cell membranes of both terrestrial and marine organisms.18) Sphingolipids attracted much attention in recent years due to their involvement in various cellular processes including cell growth, survival, differentiation, and adhesion. 19,20)
Results and DiscussionRepeated column chromatography of EtOAc solubles of the methanolic extract of the organism followed by purification by medium pressure liquid chromatography (MPLC) afforded compounds 1-5 as colourless solids. The IR spectra of 1-3 suggested the presence of hydroxyl and amide groups while the UV spectra had no characteristic signals above 210 nm. Close examination of 1 H-and 13 C-NMR spectra of 1-3 (Table 1) revealed the presence of NH, carbonyl, end methyls and long aliphatic chain suggesting sphingolipid skeleton. . The stereochemistries at C-2, C-3 and C-2Ј were assigned 2S, 3R and 2ЈR by comparing the NMR and optical rotation data with those of natural and synthetic sphingolipids. [24][25][26][27] The geometry of the double bonds was taken as trans (4E,8E) on the basis of large coupling constants (15.3, 15.0 Hz). Chemical investigation of a soft coral species of the genus Lobophytum has resulted in the isolation of three new sphingolipids- (2S,3S,4R)-2-nonadecanoylamino-octadecane-1,3,4-triol (1), (2S,3R,4E,8E)
