Separation Of Saccharomyces Cerevisiae Thornasterside And BF ₃ · SiO ₂ Removal Of Acetylated Isopropylidene By Ultrasonic

1. Synthesis of the pentasaccharide moiety of Thornasteroside AAsterosaponins, the predominant secondary metabolites in starfishes, possess important physiological activities, such as anti-virus, anti-tumor, etc. So far, hundreds of asterosaponin molecules have been isolated. However, the limitation of separation and extraction lead to that it is difficult to get a sufficient amount of asterosaponins for further research. Thus, an efficient chemical synthesis method should be developed to solve this problem.Thornasteroside A, the first asterosaponin isolated from starfishes in1978, possesses the typical structural features of asterosaponin. Moreover, the cabohydrate residue of thornasteroside A is a pentasaccharide with the sequence of [β-D-Quip-(1→2)]-[β-D-Fucp-(1→2)-β-D-Galp-(1→4)]-β-D-Xylp-(1->3)-p-D-Quip, which is scarce in nature. The efficient synthesis of the pentasaccharide moiety of Thornasteroside A has been completed for the first time. Initially, a [3+2] convergent strategy was attempted, while the1,2-trans glycosidic linkage of galactopyranose with xylopyranose was not formed in the absence of neighboring group with Pd(CH3CN)2(BF4)2. With "solvent effect", the1,2-trans glyconsidic bond was formed in50%stereoselectivity and15%yield. Subsequently, a [3+1+1] strategy was adopted. The galactopyranose (48) equipped with a neighboring participating Lev (levulinoyl) group at the C2-OH was first coupled with the trisaccharide acceptor to construct the1,2-trans glyconsidic bond. Then the Lev group was selectively removed and followed by glycosylation with the perbenzoylated D-Fucopyranosyl Schmidt donor (8) to providde the desired pentasaccharide efficiently.The current work reported here would significantly facilitate the total synthesis of the whole Thornasteroside A molecule and other structure related oligosaccharides that isolated from starfishes and other marine organisms.2. Ultrasound-assisted Selective Deprotection of Terminal Acetonides Catalyzed by Silica-supported Boron TrifluorideAn efficient and convenient method for the selective cleavage of terminal isopropylidene is described. Treatment of terminal isopropylidenes over a wide range of functional groups with silica-supported boron trifluoride as a catalyst, furnished the corresponding diols in high yields under ultrasound irradiation conditions.