101(P-50) チオグリコシドを用いた連続的なグリコシル化反応(ポスター発表の部)

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Intensive efforts have been recently aimed at the synthesis of oligosaccharides because of their numerous important biological functions. Because oligosaccharides consist of several monosaccharides by means of anomeric C-O bond linkage, various new glycosylation methods have been developed recently to increase the efficiency for the iterative coupling sequences. In this respect, we have already reported a new iterative glycosylation using selenoglycosides as both gycosyl donors and acceptors. This method involves in situ conversion of selenoglycosides to the reactive β-bromoglycosides, which undergo the coupling reaction with selenoglycosides bearing hydroxyl group. Since the products also possessed the arylselenyl group as the anomeric substituent, they could be directly used for the next glycosylation reaction. While this method is suitable for the iteration of glycosylation, it suffers several drawbacks; the low reactivity of β-bromoglycosides due to the strong covalent C-Br bond and the difficulty to synthesize 1,2-cis-glycosides. To overcome these drawbacks, we have investigated a new iterative method that mediates reactive glycosyl cation intermediates generated from thioglycosides. Treatment of benzoyl protected phenylthioglucopyranoside with PhSSbF6 at -78 oC followed by addition of C-6 hydroxyl phenylthioglucopyranoside afforded the corresponding glycoside 1,2-ortho ether, which was isomerized to the desired disaccharide upon treatment with a catalytic amount of TfOH. While variety of activating reagent possessing different counter ion, such as PhSOTf, PhSBF4, PhSPF6, and PhSSbF6, were also examined, the use of PhSSbF6 as the activator showed the highest coupling efficiency. Acyl-protected thioglycosides derived from galactose could be also glycosylated under similar conditions. Alkyl-protected thioglycosides, on the other hands, could be best activated by benzenesulfinylpiperidine and Tf2O and give α-anomer of the desired disaccharide as a major product.
天然有機化合物討論会の論文
2002-09-01

101(P-50) チオグリコシドを用いた連続的なグリコシル化反応(ポスター発表の部)

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