Holothurin structure

Several holothurins are specific for different taxonomic groups of sea cucumbers and structural characteristics of triterpene glycosides have been used to resolve taxonomic problems in the class Holothuroidea [57, 58]. For example, the triterpenoid glycosides distribution has been successfully applied in the reclassification of Stichopus mollis into the genus Australostichopus [59] and in the taxonomy of sea cucumbers belonging to the genus Cucumaria [60]. 

Five non-sulfated triterpene glycosides, synallactosides Ai (52a), A2 (52b), Bi (52c), B2 (52d) and C (52e), Fig. (21) were isolated from the deep-water North Pacific sea cucumber Synallactes nozawai [73]. Synallactoside Ai is the 25,26-dehydro derivative of thelenotoside A, isolated from Thelenota ananas as a mixture with thelenotoside A [74]. Compounds 52b-52e are new compounds with interesting features in the carbohydrate chains of synallactosides A2, Bi, and B2. Synallactoside A2 (52b) is the first glycoside isolated from sea cucumbers with two terminal 3-(9-methylxylose residues in the oligosaccharide chain. On the other hand, the carbohydrate chains of synallactosides Bi (52c) and B2 (52d) have unprecedent structures among holothurins. 

Fig. (24). Structure of Patagonicoside A, an antifungal holothurin isolated from the sea cucumber Fsolus patagonicus and its desulfated derivative...

Holothurin B R = Qui-(I-42)-4-0S03Na-XyI Fig. (28). Structure of Holothurin B3 from the sea cucumber Holothuria polii... 

The complete structure (27) of holothurin B, a saponin from the sea cucumber Holothuria leucospilota, has been established. A new sapogenin from another sea cucumber, Bohadschia vitiensis, has been assigned structure (28). Several papers dealing with the synthesis of sechellogenin (29) have appeared. Functionalization of C-18 was achieved by nitrite photolysis. 

Kitagawa, I., T. Nishino, M. Kobayashi, and Y. Kyogoku Marine Natural Products. VIII. Bioactive Triterpene-Oligoglycosides from the Sea Cucumber Holothuria leucospilota Brandt (2). Structure of Holothurin A. Chem. Pharm. Bull. (Japan) 29, 1951 (1981). 

Kalinin, V.I., and V.A. Stonik Glycosides of Marine Invertebrates. Structure of Holothurin A2 from the Holothurian Holothuria edulis. Khim. Prir. Soedin. 1982, 215. 

Another general observation is that the holothurins are structurally more homogeneous than the saponins of sea stars. On the carbon skeleton of holostane there are only about 20 side chains and some 30 osidic parts, whereas more than 150 side chains and more than 50 osidic parts have been found in asterosaponins and related derivatives. 

The hemolytic properties of holothurins seem to be correlated with the presence and position of the sulfate groups on the various oses. Thus, the presence of a sulfate group at position 4 on the xylose linked to the aglycone increases hemolytic activity, whereas a sulfate group at position 6 on the third ose reduces it (Kalinin et al, 1992, 1996b). Several holothurins, especially holothurin B, are also antifungal, but no structure-activity relationship seems to have been observed (Kumar et al, 2007). 

---