O-Glycosyl Donors
3.4
601
⊡ Scheme 30
Reactive intermediates from different glycosyl donors
⊡ Table 9
Competition studies on the glycosylation of acceptor 215 in the presence of glycosyl donors (64 and 200 or 202b)
with variable amounts of NIS
Entry Donors
NIS
Product ratio
Yield
armed/disarmed
(equiv) 216
217 (%)
i
64
200
1
2
1.1
57
ii
64
200
3
1.1
1
69
iii
64
202b
1
1
0
52
iv
64
202b
3
1
2.2
83
2.11 NPGs in Oligosaccharide Synthesis
Since their discovery, the unique properties of NPGs have allowed the preparation of several oligosaccharides. The pentenyl moiety may be installed early in the synthetic sequence
and can survive many types of protecting group manipulations. Some selected syntheses of
oligosaccharides are briefly discussed below.
2.11.1 The Pentasaccharide Core of the Protein Membrane Anchor Found
in Trypanosoma brucei
Fraser-Reid and co-workers described a block (i. e., convergent), and a linear approach to the
title compound, 226 ( > Scheme 31) [114]. The convergent approach, outlined in > Scheme 31,
3.4
601
⊡ Scheme 30
Reactive intermediates from different glycosyl donors
⊡ Table 9
Competition studies on the glycosylation of acceptor 215 in the presence of glycosyl donors (64 and 200 or 202b)
with variable amounts of NIS
Entry Donors
NIS
Product ratio
Yield
armed/disarmed
(equiv) 216
217 (%)
i
64
200
1
2
1.1
57
ii
64
200
3
1.1
1
69
iii
64
202b
1
1
0
52
iv
64
202b
3
1
2.2
83
2.11 NPGs in Oligosaccharide Synthesis
Since their discovery, the unique properties of NPGs have allowed the preparation of several oligosaccharides. The pentenyl moiety may be installed early in the synthetic sequence
and can survive many types of protecting group manipulations. Some selected syntheses of
oligosaccharides are briefly discussed below.
2.11.1 The Pentasaccharide Core of the Protein Membrane Anchor Found
in Trypanosoma brucei
Fraser-Reid and co-workers described a block (i. e., convergent), and a linear approach to the
title compound, 226 ( > Scheme 31) [114]. The convergent approach, outlined in > Scheme 31,