Facile synthesis of tetrasaccharide fragments of bioactive Asterosaponins novaeguinosides I and II from starfish Culcita novaeguineae

Simple and straightforward synthesis of tetrasaccharide fragments of novaeguinosides I and II, isolated from the starfish Culcita novaeguineae that showed significant in vitro cytotoxicity activity against two human tumor cell lines (leukemia K-562 and hepatoma BEL-7402) is reported. The tetrasaccharide moieties have been synthesized as their p-methoxyphenyl (PMP) glycosides by sequential glycosylation strategy using suitably functionalized thioglycoside donors employing sulfuric acid immobilized on silica (H2SO4–silica) as a Brönsted acid catalyst to work as a promoter for all glycosylation reactions. All intermediate steps are high yielding and the glycosylation steps are stereoselective.