Progress in the chemistry of glycoconjugates during the last decade reflects the availability of a wide array of methods for stereoselective 0-glycosylation'-3. Carbohydrate segments of biological interest can be coupled through a spacer4 to a soluble protein to yield synthetic antigens, and attachment to solid phases leads to immunoadsorbents. Spacer-arm glycosides have been made5 and used6 for several purposes. Our studies of the synthesis of the lipopolysaccharide of Proteus sps. culminated in the development of a method for the synthesis of 2-azidoethyl P-glycosides' and was utilised for the synthesis of determinants as neoglycoconjugatess,9 which gave positive serodiagnostic results.
The stereoselective synthesis of a-linked saccharides is important since they are constituents of many biologically active glycoconjugatess. We now report an extension of the methodology for glycosylation with 2-pyridyl l-thioglycosideslO~'l for the synthesis of 2-azidoethyl a-glycosides.
The glycosyl donor 2-pyridyl 2,3,4-tri-0-benzyl-6-0-trityl-l-thio+o-glucopyranoside (1) was prepared from 1,2,3,4,6-penta-0-acetyl-P_D-glucopyranose; 2pyridyl 2,3,4,6-tetra-O-benzyl-l-thio-P-o-galactopyranoside (21, 2-pyridyl 2,3,4-tri-0-benzyl-l-thio-a$-L-rhamnopyranoside (3), and 2-pyridyl 2,3,.5-tri-O-benzyl-lthio-/?-D-ribofuranoside (4) were prepared by known procedures'O,"; and 2-pyridyl 2,3,6-tri-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-~-~-galactopyranosyl~-l-thio-~-oglucopyranoside (5) was obtained from cu-acetobromolactose'2 by adapting a reported" procedure. When the 2-pyridyl 1-thioglycosides l-5 (1.0 mmol) were each heated with 2-azidoethanol(3 mmol) in anhydrous dichioromethane (10 mL, containing 3% of methyl iodide) in the presence of 4A molecular sieves at 50°C (12-72 h), the ' IICT Communication No. 3074.