Phytosphingosine moiety

On hydrolysis, Ci8- (17-33%) and C2o-phytosphingosine (56-75%), and C18-dihydrosphingosine (6-7 %) were obtained. In amide linkage on the phytosphingosine moiety are saturated and unsaturated fatty acids for example, lignoceric acid (4-8%) and cerebronic acid (36-56%). 

The composition of the ceramide moiety of these glycolipids is quite similar. Among the fatty acids, normal and a-hydroxy acids were detected the latter accounted for 10% of the mixture of acids. In the monosialogly-colipid, the major components of the normal acids are C14 0 and C16 0 acids, and of the a-hydroxy acids, the C15 0, C17 0, and C24 0 a-hydroxy acids. The sphingosine bases are phytosphingosines the preponderant ones are C18 and C19 phytosphingosines.140,293... 

Comparison of C NMR chemical shifts of C-2 (51.7 ppm), C-3 (75.8 ppm), and C-4 (72.5 ppm) in phytosphingosine-type bases with that of synthetic isomers at C-2, C-3, and C-4 confirmed the (25,3/ ,45)-configuration in natural sphingolipids and the power of NMR for this assignment [26]. C NMR signals for terminal methyl groups in the ceramide moiety are indicative... 

The presence of 2-hydroxylated fatty acids can be easily determined by C NMR spectroscopy in cerebrosides containing sphingosine-type bases due to the chemical shift of C-2 (72.5 ppm). In cerebrosides with phytosphingosine-type bases, C-4 in the long-chain base and C-2 hydroxy-lated in the fatty acid moiety show similar chemical shifts [6]. 

A phytosphingosine-type galactocerebrosides mixture (12) with nonhy-droxylated and hydroxylated fatty acyl moieties (Fig. 8) was isolated from the starfish Culcita novaeguineae [49]. This was the second report of galactocerebrosides in echinoderms, being the first that of the starfish Stellaster equestris [50]. 

Chemical examination of the sea cucumber Holothuria leucospilota led to the isolation of a phytosphingosine-type glucocerebroside (40) with a 2-hydroxylated fatty acid of 22 carbons and an anteiso type side chain in the base moiety (Fig. 12) [55]. The absolute configuration of the branched methyl group was determined by release of a C13 fragment of the native cere-broside and further reduction to 10-methyl dodecanol. The absolute configuration of the natural alcohol was elucidated by comparison with synthetic optically active 10-methyl dodecanol synthesized from 1,4-butanediol [56]. 

Furthermore, instead of the fourth step of desaturation, yeast introduce a hydroxyl group on C-4 of dihydrosphingosine or dihydroceramide, forming phytosphingosine or phytoceramide. The structural features of typical sphingoid moieties are illustrated in Figure 1. 

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