Synthesis of a common pentasaccharide moiety of diplasteriosides A and B belong to starfish asterosaponins isolated from the Diplasterias brucei

• Published in: Tetrahedron letters 2020-10, Vol.61 (42), p.152421, Article 152421
• Main Authors: Sangwan, Rekha, Nath Mishra, Vijay, Kumar Mandal, Pintu
• Format: Article
• Language: English
• Subjects: Diplasteriosides; Glycosylation; H2SO4-silica; Natural products; Steroidal glycosides
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/j.tetlet.2020.152421

[Display omitted] •Synthesis of a common pentasaccharide moiety of diplasteriosides A and B.•Use of one-pot glycosylation-deprotection strategy in a more step-economic way.•Use of Fmoc carbonate as an orthogonal protecting group.•Sulfuric acid immobilized on silica (H2SO4–silica) as a Brönsted acid catalyst. Bearing the pentasaccharide moiety of diplasteriosides A and B, new asterosaponins isolated from the Antarctic Diplasterias brucei starfish showing potent cytotoxic activity against the different human cancer cell lines, has been synthesized as their p-methoxyphenyl (PMP) glycosides. A one-pot sequential glycosylation-deprotection strategy has been adopted for the construction of the pentasaccharide derivative, which was then transformed into target compound after global deprotection. The synthetic method relies on the use of Fmoc carbonate as an orthogonal protecting group which can be removed and the product subsequently glycosylated to reduce the number of reaction steps significantly. Here H2SO4–silica has been used alternatively as a Bronsted acid catalyst for all glycosylation reactions. All the glycosylation steps are high yielding and stereoselective.