The structure of several ceramides and cerebrosides, from three marine sponges and a soft coral collected in the Red Sea, are reported. Specifically, the structure determination of ptiloceramide, halicerebroside A and amphicerebrosides B-F was achieved following suitable degradations and NMR measurements.
The first recognition of glycolipids in a variety of marine invertebrates came in the early 197O's.l It was suggested that these glycolipids contain free and acylated cerebroside-like lipids. At the same time Karlsson* determined the structure of a cerebroside isolated from the sea star Asterias rubens, and it has been shown that the latter compound has a more complex structure than the relatively simple brain cerebrosides.' However, very few reports on the exact structures of other marine glycosphingolipids have been made until most recently.4-7 The latter reports of the isolation and characterization of new glycosphingolipids from the sea anemone Anemona sulcata 4 the starfish Acanthaster plancl, 5 --I the sponge Chondrovsis SE. 6 and from the sea hare ADlVSia kurodai7 have. led us to publish our results on related compounds. Spectroscopic (mainly NMR) as well as chromatographic methods' have shown that quite a few of the marine organisms we have investigated (sponges. tunicates and soft corals) contain ceramides and cerebrosides. Thus, a sphingosine derivative (1, Fig.1) was separated from Reteroxenia eardaauensis collected at the entrance to the Gulf of Suez. a
This compound was found to be erythro-docosasphinga-4,S-dienine, identical with the most recently reported metabolite of Anemona sulcata. 4
Another ceramide was isolated from Ptilocaulis soiculifer. After several chromatographies on Sephadex LH-20 eluted with hexane-chloroform 3~7 or chloroformmethanol l:l, we isolated from the ethyl acetate extract of this sponge a fraction exhibiting antifungal activity (Candid@ plbicans, MIC-12.5 @ml). Final purification of the active components, named ptiloceramides (&), was achieved following acetylation and chromatography of the tetraacetyl derivatives (a) on a silica gel column. This mixture of tetraacetyl ptiloceramides (a) exhibited in the mass spectra (DCI, isobutane) a series of peaks at m/z: 852, 838, 824, 810 and 796(MH+), suggesting five homologues (Fig.1) which were not further separated. The sequence of the C-l to C-5 moiety in a, which includes three hydroxyls and an amide functionality (Fig.l), was established by a COSY experiment which correlated all the corresponding protons, including the IQ signal (6H 6.60-7.40ppm; a region which is characteristic for the NH in glycosphingolipids).