Di-tert-butylsilylene-directed alpha-selective synthesis of p-nitrophenyl T-antigen analogues

Seven analogues of p-nitrophenyl T-antigen [Gal beta(1 -> 3)GalNAc alpha(1 -> O)PNP] have been synthesized as potential substrates for elucidation of the substrate specificity of endo-alpha-N-acetylgalactosaminidase. These compounds, which are commercially unavailable, include: GlcNAc beta(1 -> 3){GlcNAc beta(1 -> 6)}GalNAc alpha(1 -> O)PNP [core 4 type], GalNAc alpha(1 -> 3)GalNAc alpha(1 -> O)PNP [core 5 type], GlcNAc beta(1 -> 6)GalNAc alpha(1 -> O)PNP [core 6 type], GalNAc alpha(1 -> 6)GalNAc alpha(1 -> O)PNP [core 7 type], Gal alpha(1 -> 3)GalNAc alpha(1 -> O)PNP [core 8 type], Glc beta(1 -> 3)GalNAc alpha(1 -> O)PNP and GalNAc beta(1 -> 3)GalNAc alpha(1 -> O)PNP. The assembly of these synthetic probes was accomplished efficiently, based on di-tert-butylsilylene(DTBS)-directed alpha-galactosylation as a key reaction.