Syntheses of an α-d-Gal-(1→6)-β-d-Gal diglyceride, as lipase substrate

Two different routes were explored to afford 3-O-(6-O-α-d-galactopyranosyl-β-d-galactopyranosyl)-1,2-di-O-dodecanoyl-sn-glycerol. In the first one, the key step was the glycosylation of the 3-O-(2,3,4-tri-O-benzyl-β-d-galactopyranosyl)-1,2-O-isopropylidene-sn-glycerol acceptor with 2-pyridyl 2,3,4,6-tetra-O-benzyl-1-thio-β-d-galactopyranoside as the donor. In the second one, the key step was the coupling of 2,3,4-tri-O-acetyl-6-O-(2,3,4,6-tetra-O-benzyl-α-d-galactopyranosyl)-d-galactopyranosyl trichloroacetimidate donor with 1,2-O-isopropylidene-sn-glycerol. Even though the number of steps was the same in both pathways, the first one afforded a better overall yield (12.4%) than the second one (6.5%). This eight-step synthesis allowed the preparation of the expected glycolipid, which was used as substrate for recombinant GPLRP2 galactolipase using the monomolecular film technique.

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