O-Glycosyl Donors
3.4
625
protected disaccharide, 339. Compound 339 can be elaborated into linear or branched trisaccharides 342 and 343. Thus, deprotection of the acetyl group in 339, and glycosylation with
vinyl donor 336 will yield linear trisaccharide 342, whereas removal of the PMB group and
coupling with 337 will produce orthogonally protected branched trisaccharide 343.
3.3.3 3-Buten-2-yl 2-amino-2-deoxy Glycosides as Glycosyl Donors
Boons and co-workers studied the use of 3-buten-2-yl 2-azido-2-deoxy, and 2-deoxy-2phthalimido glycosides, as building blocks for the preparation of sugar containing oligosaccharides [182]. Vinyl glycoside donors 344, 346, and 348, were uneventfully prepared by
isomerization of the corresponding 3-buten-2-yl glycosides with (Ph 3 )P 3 RhCl/BuLi in yields
exceeding 90%. Several glycosyl acceptors were used in the study, although representative
data in > Scheme 56 refer solely to acceptor 300. The glycosylation with azido donor 344,
in MeCN using TMSOTf as the promoter at −30 °C, proceeded with high β-selectivity
( > Scheme 56a), whereas NIS/TMSOTf in a dioxane/toluene mixture gave good α-selectivities ( > Scheme 56c). 2-Buten-2-yl 2-deoxy-2-phthalimido glycosides 346 and 348 reacted
in CH 2 Cl 2 in the presence of a catalytic amount of TMSOTf to give only the β-linked
disaccharides 347 and 349, respectively.
3.3.4 An Approach for Heparin Synthesis Based on 3-Buten-2-yl Glycosides
Haller and Boons described an approach fully based on 3-buten-2-yl glycosides for the synthesis of trisaccharide 350 and sulfated disaccharide 351 ( > Scheme 57) [183]. In their strategy
the glucuronic acid moieties were introduced at a late stage of the synthetic sequence by selective oxidation of primary hydroxyl groups with TEMPO and NaOCl. “Latent” allyl glycoside
353 functioned as an acceptor for the reducing end in compounds 350 and 351, and was also
transformed to “active” vinyl glycoside 352, for the nonreducing unit of 350. The 2-aceta⊡ Scheme 57
3-Buten-2-yl derivatives for the synthesis of amino sugar containing oligosaccharides
3.4
625
protected disaccharide, 339. Compound 339 can be elaborated into linear or branched trisaccharides 342 and 343. Thus, deprotection of the acetyl group in 339, and glycosylation with
vinyl donor 336 will yield linear trisaccharide 342, whereas removal of the PMB group and
coupling with 337 will produce orthogonally protected branched trisaccharide 343.
3.3.3 3-Buten-2-yl 2-amino-2-deoxy Glycosides as Glycosyl Donors
Boons and co-workers studied the use of 3-buten-2-yl 2-azido-2-deoxy, and 2-deoxy-2phthalimido glycosides, as building blocks for the preparation of sugar containing oligosaccharides [182]. Vinyl glycoside donors 344, 346, and 348, were uneventfully prepared by
isomerization of the corresponding 3-buten-2-yl glycosides with (Ph 3 )P 3 RhCl/BuLi in yields
exceeding 90%. Several glycosyl acceptors were used in the study, although representative
data in > Scheme 56 refer solely to acceptor 300. The glycosylation with azido donor 344,
in MeCN using TMSOTf as the promoter at −30 °C, proceeded with high β-selectivity
( > Scheme 56a), whereas NIS/TMSOTf in a dioxane/toluene mixture gave good α-selectivities ( > Scheme 56c). 2-Buten-2-yl 2-deoxy-2-phthalimido glycosides 346 and 348 reacted
in CH 2 Cl 2 in the presence of a catalytic amount of TMSOTf to give only the β-linked
disaccharides 347 and 349, respectively.
3.3.4 An Approach for Heparin Synthesis Based on 3-Buten-2-yl Glycosides
Haller and Boons described an approach fully based on 3-buten-2-yl glycosides for the synthesis of trisaccharide 350 and sulfated disaccharide 351 ( > Scheme 57) [183]. In their strategy
the glucuronic acid moieties were introduced at a late stage of the synthetic sequence by selective oxidation of primary hydroxyl groups with TEMPO and NaOCl. “Latent” allyl glycoside
353 functioned as an acceptor for the reducing end in compounds 350 and 351, and was also
transformed to “active” vinyl glycoside 352, for the nonreducing unit of 350. The 2-aceta⊡ Scheme 57
3-Buten-2-yl derivatives for the synthesis of amino sugar containing oligosaccharides