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The terminal glycosyl acceptor methyl 2,3-di-O-benzyl-α-L-fucopyranoside (6) was extended three times with the non-terminal glycosyl donor ethyl 4-O-acetyl-2,3-di-O-benzyl-1-thio-ß-L-fucopyranoside (13) via iodonium-ion assisted glycosylations and intermittent removal of the C-4 acetyl group in intermediate dimer 16 and trimer 18. The 4-O-acetyl group in trimer 18 and tetramer 20 was highly resistant towards basic hydrolysis. The latter could be nullified by using dichloroacetyl instead of acetyl to protect the C-4-OH in the donor. The exclusive formation of 1,2-cis-linked oligomers could be explained by through-bond interactions exerted by the electron-withdrawing C-4 acyl group in the glycosyl donor.

Easily accessible 1,6-anhydro-2,3-O-(S)-benzylidene-β-D-mannopyranose was converted in four steps to 1,6-anhydro-3,4-di-O-benzyl-β-D-talopyranose. Glycosylation of the latter with ethyl 2,3,4-tri-O-acetyl-1-thio-α-L-rhamnopyranoside gave, after further processing, 1-O-allyl-3,4-di-O-benzyl-2-O-(2,3,4-tri-O-benzyl-α-L-rhamnopyranosyl)-L-ribitol.

Block condensation of fully protected donor ethyl 1,2,3,4-tetra-O-benzyl-D-Rib-(5→P→6)-2,3,4-tri-O-benzoyl-l-thio-β-D-Glcp (2), having a (5→6)-phosphotriester union between the ribitol and the glucopyranosyl moieties, with the free 3'-OH group in the acceptor methyl 2-acetamido-4-O-(2-acetamido-4-(benzyloxycarbonyl)amino-2,4,6-trideoxy-α-D-Galp)-3,6-di-O-benzyl-2-deoxy-α-D-Galp (3), under the agency of N-iodosuccinimide and triflic acid, gave the fully protected tetrameric fragment 22. Elimination of the 2-cyanoethyl group from the phosphotriester and subsequent debenzoylation, followed by hydrogenolysis of the benzyl and benzyloxycarbonyl groups provided the target tetramer methyl D-Rib-(5→P→6)-D-Glcp-β(1→3)-Sugp-α(1→4)-α-D-GalpNAc (1).