622
3
Chemical Glycosylation Reactions
promoted condensation of 327 with 328 in MeCN gave disaccharide 329 as the β-anomer
mainly (α/β = 1:8) ( > Table 11, entry i). An improved α-selectivity was obtained (73%,
α/β = 3:1) when the coupling was performed in ether/dichloroethane ( > Table 11, entry iv).
3.3.2 Preparation of Trisaccharide Libraries
Linear Trisaccharide Libraries Boons et al. described an approach to combinatorial synthesis of trisaccharide libraries based on their latent-active glycosylation strategy [180]. One
major building block, 330 (i. e. B 1 , > Scheme 54) can be converted into a glycosyl donor 331
(i. e. D 1 ) and a glycosyl acceptor 332 (i. e. A 1 ). Coupling of compounds 331 and 332 gives disaccharide 333a in excellent yield (the anomeric ratio can be greatly influenced by changes in
the temperature: α/β = 1:20 at low temperature; α/β = 1:1 at ambient temperature). The latter
can be converted into a glycosyl acceptor 333b (i. e. D 1 A 1 ) by removing the acetyl protecting
⊡ Scheme 54
Preparation of linear trisaccharide libraries
3
Chemical Glycosylation Reactions
promoted condensation of 327 with 328 in MeCN gave disaccharide 329 as the β-anomer
mainly (α/β = 1:8) ( > Table 11, entry i). An improved α-selectivity was obtained (73%,
α/β = 3:1) when the coupling was performed in ether/dichloroethane ( > Table 11, entry iv).
3.3.2 Preparation of Trisaccharide Libraries
Linear Trisaccharide Libraries Boons et al. described an approach to combinatorial synthesis of trisaccharide libraries based on their latent-active glycosylation strategy [180]. One
major building block, 330 (i. e. B 1 , > Scheme 54) can be converted into a glycosyl donor 331
(i. e. D 1 ) and a glycosyl acceptor 332 (i. e. A 1 ). Coupling of compounds 331 and 332 gives disaccharide 333a in excellent yield (the anomeric ratio can be greatly influenced by changes in
the temperature: α/β = 1:20 at low temperature; α/β = 1:1 at ambient temperature). The latter
can be converted into a glycosyl acceptor 333b (i. e. D 1 A 1 ) by removing the acetyl protecting
⊡ Scheme 54
Preparation of linear trisaccharide libraries