680
3
Chemical Glycosylation Reactions
2.2.5 Via 1,2-Thiazoline Derivatives (2-Acetamido Donors)
Treatment of peracetylated 2-acetamido-β-D-gluco- or galacto-pyranose with the Lawesson’s
reagent gave the corresponding 1,2-thiazoline derivatives in quantitative yield ( > Scheme 41).
Consecutive hydrolysis using TFA in wet methanol yielded the corresponding anomeric α-thiols, which were then acetylated to the α-thioacetate or alkylated in various ways (compare
> Sect. 2.3 below) to give a number of different α-thioglycosides [145,146,147].
⊡ Scheme 41
Another efficient way to 2-acetamido thiosugars is described from a 2-azido-1-chloro precursor. The β-thioacetate of 2-acetamido-2-deoxy-lactose was obtained by treatment of the
2-azido-2-deoxy α-chloride with a large excess of thioacetic acid, which both displaced the
chloride and concomitantly reduced and acetylated the azido group ( > Scheme 42) [148].
⊡ Scheme 42
2.2.6 Via Glycosyl Thioimidocarbonates and Diglycosyl Disulfides
Other miscellaneous 1-thio derivatives convertible to thioaldoses are glycosyl thioimidocarbonates and diglycosyl disulfides [1]. Their syntheses are similar to the ones described above,
i. e., displacement reactions of an acylated glycopyranosyl halide with a thionucleophile, an
⊡ Scheme 43
3
Chemical Glycosylation Reactions
2.2.5 Via 1,2-Thiazoline Derivatives (2-Acetamido Donors)
Treatment of peracetylated 2-acetamido-β-D-gluco- or galacto-pyranose with the Lawesson’s
reagent gave the corresponding 1,2-thiazoline derivatives in quantitative yield ( > Scheme 41).
Consecutive hydrolysis using TFA in wet methanol yielded the corresponding anomeric α-thiols, which were then acetylated to the α-thioacetate or alkylated in various ways (compare
> Sect. 2.3 below) to give a number of different α-thioglycosides [145,146,147].
⊡ Scheme 41
Another efficient way to 2-acetamido thiosugars is described from a 2-azido-1-chloro precursor. The β-thioacetate of 2-acetamido-2-deoxy-lactose was obtained by treatment of the
2-azido-2-deoxy α-chloride with a large excess of thioacetic acid, which both displaced the
chloride and concomitantly reduced and acetylated the azido group ( > Scheme 42) [148].
⊡ Scheme 42
2.2.6 Via Glycosyl Thioimidocarbonates and Diglycosyl Disulfides
Other miscellaneous 1-thio derivatives convertible to thioaldoses are glycosyl thioimidocarbonates and diglycosyl disulfides [1]. Their syntheses are similar to the ones described above,
i. e., displacement reactions of an acylated glycopyranosyl halide with a thionucleophile, an
⊡ Scheme 43