Studies directed towards the synthesis of sulphated and non‐sulphated glyco‐conjugate fragments using insoluble silver‐salt promoters

The synthesis of three fucosylated oligosaccharides (i.e. compounds 8, 10 and 14) and a keratan sulphate fragment (i.e. compound 24) is presented. The formation of β bonds in these glyco‐conjugate fragments was promoted by insoluble silver salts, while non‐participating groups are present at C‐2 of the glycosyl bromide. Thus, glycosyl donors can be used which have also been employed for a glycoside synthesis. It was found that insoluble silver salt promoters can be very worthwile for the formation of β bonds in larger oligosaccharides when relatively reactive glycons with suitable substitution pattern are condensed with reactive aglycons. The application of this coupling methodology is of special advantage for the synthesis of functionalized oligosaccharides (such as 24), which synthesis may require the use of building blocks having non‐participating (e.g. benzyloxy or azido) protecting groups at C‐2.