Chemical synthesis of marine saponins.

Covering: 1989-2017 Saponins are characteristic metabolites of starfish and sea cucumbers, and occasionally are also found in sponges, soft coral, and small fish. These steroid or triterpenoid glycosides often show remarkable biological and pharmacological activities, such as antifungal, antifouling, shark repellent, antitumor and anti-inflammatory activities. Over one thousand marine saponins have been characterized; the majority of them can be categorized into three major structural types, i.e., asterosaponins, polyhydroxysteroid glycosides, and holostane glycosides. Thus far, only 12 marine saponins have been synthesized; those representing the major types were successfully synthesized recently. The syntheses involve preparation of the aglycones from the terrestrial steroid or triterpene materials, installation of the carbohydrate units, and manipulation of the protecting groups. Herein, we provide a comprehensive review on these syntheses.

Total Synthesis of Echinoside†A, a Representative Triterpene Glycoside of Sea Cucumbers.

Echinoside A, a sulfonylated holostane tetrasaccharide with potent anticancer and antifungal activity, was synthesized in a longest linear sequence of 35 steps and 0.6 % overall yield. The synthetic approach is adaptable to the synthesis of congeners and analogues, as exemplified by the ready synthesis of ds-echinoside A and echinoside B, and thus will facilitate in-depth studies on the promising biological effects of echinoside A. Moreover, the present synthesis demonstrates the feasibility of synthetic access to the characteristic complex triterpene glycosides that occur ubiquitously in sea cucumbers.