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Saponins, water soluble compounds composed of sugars and steroid or triterpenoid moieties, have attracted considerable interests due to the increased understanding of their wide spectrum of biological and pharmacological activities.Saponins have been found only in marine phylum Echinodermata and particularly in species of the classes Holothuroidea (sea cucumbers) and Asteroidea (starfishes) in the animal kingdom. Starfish extracts and also purified saponins have shown a broad spectrum of physiological and pharmacological activities. In 1981, Sepositoside A, the major saponin, was isolated from the hydrolysate of the Mediterranean starfish Echinaster sepositussaponins mixture(Figure 1). It has a number of unusual features when compared to the more common asterosaponins: it is devoid of the sulphate group and the Δ7, 3β,6β-dioxygenated steroidal nucleus is unprecedented, and, the most remarkable feature is that the trisaccharide chain is cyclized between C-3 and C-6 of the aglycon, giving rise to a highly strain 16-membered macrocyclic ring reminiscent of a crown ether. Sepositoside A had been shown to display antifungal activity, cytotoxic acitivity toward bovine turbinate cells up to a level of 1 μg ml-1 and inhibition of cell division of fertilized sea urchin eggs (ca. 30% inhibition at 10-5 M).Fascinated by the unprecedented highly strain 16-membered macrocyclic molecular structure of Sepositoside A, we contemplated its total synthesis, which might require new synthetic strategies and technologies to close the challenging 16-membered macrocyclic ring by virtue of its expected high strain and lability. Herein, we report our synthetic studies for the construction of 16-membered macrocyclic ring of Sepositoside A model systems.