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Oligosaccharide Analogues of Polysaccharides
Author(s) -
Hoffmann Barbara,
Bernet Bruno,
Vasella Andrea
Publication year - 2002
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(200201)85:1<265::aid-hlca265>3.0.co;2-1
Subject(s) - chemistry , intramolecular force , propargyl alcohol , glycosylation , stereochemistry , alkyne , oligosaccharide , propargyl , cycloaddition , acetal , glycoside , organic chemistry , catalysis , biochemistry
The α ‐ and γ ‐CD analogues 6 and 18 , which possess a hexa‐2,5‐diyne‐1,6‐dioxy unit, were synthesised by intramolecular coupling of the bis‐ O ‐propargylated maltohexaoside 4 , or the analogous maltooctaoside 16 , followed by deprotection. The dialkynylated linear oligosaccharides were obtained by glycosidation of propargyl alcohol with the thioglycosides 1 and 13 , reductive cleavage of the benzylidene acetal, and propargylation of the terminal HO−C(4) group, respectively. The β ‐CD analogues 23 and 25 , which possess a penta‐1,3‐diyn‐1‐yl‐5‐oxy unit, were similarly obtained by intramolecular oxidative coupling of 20 and 21 , respectively. The linear dialkynylated oligosaccharides 20 and 21 were obtained by two consecutive glycosylations, first with the maltohexaosyl‐ S ‐glycoside 1 as donor, and then by glycosylation of the resulting propargyl maltohexoside with the C (4)‐ethynylated donor 19 . The proximity of the terminal units of maltooligosaccharides allowed a facile intramolecular cycloaddition of the azido alkyne 29 to the isomeric triazoles 30 and 31 , which were deprotected to 32 and 33 , respectively. Analysis of the intramolecular H‐bonds in 6, 23, 25, 32 , and 33 showed that insertion of a noncarbohydrate link interrupts a single flip‐flop H‐bond.