1. Synthesis of glycosylated tuftsins and tuftsin-containing IgG fragment undecapeptide
L Biondi, B Scolaro, F Filira, R Rocchi, M Gobbo Int J Pept Protein Res . 1991 Feb;37(2):112-21. doi: 10.1111/j.1399-3011.1991.tb00090.x.
Syntheses are described of two new tuftsin derivatives containing a 2-acetamido-2-deoxy-D-galactopyranosyl unit alpha- or beta-glycosidically linked to the threonine's hydroxy side chain function and of the glycosylated undecapeptide corresponding to the tuftsin region of the heavy chain of IgG (amino acid sequence 289-299). The glycosylated tuftsins were synthesized by the solution procedure. Fmoc-[Gal NAc(Ac)3 alpha]Thr-OH and Fmoc-[GalNAc(Ac)3 beta]Thr-OH were allowed to react with H-Lys(Z)-Pro-Arg(NO2)-OBzl by the mixed anhydride procedure and the resulting glycosylated tetrapeptides were fully deblocked by catalytic hydrogenation followed by treatment with potassium cyanide, purified by ion exchange chromatography and characterized by analytical HPLC, elemental and amino acid analyses, optical rotation, and proton NMR spectroscopy. Synthesis of the glycosylated undecapeptide was achieved by the continuous flow solid phase procedure on 4-hydroxymethylphenoxyacetyl-norleucyl derivatized Kieselguhr-supported resin. Fmoc-amino acid symmetrical anhydrides or pentafluorophenyl esters, in the presence of N-hydroxybenzotriazole, were used as the acylating agents. To mimic the native sequence of the tuftsin region at the Fc-domain of immunoglobulin G a 2-acetamido-2-deoxy-beta-D-glucopyranosyl unit was N-glycosidically linked to the amide side chain of Asn 297. The glycosylated asparagine residue was introduced as N2-fluorenylmethyloxycarbonyl-N4-(2-acetamido-3,4,6-tri-O-acetyl-2 -deoxy-beta-D - glucopyranosyl)-asparagine pentafluorophenyl ester. After cleavage from the resin the glycopeptide was deprotected, purified by ion exchange chromatography, and characterized by analytical HPLC, amino acid analysis, high voltage electrophoresis, and proton NMR. The conformational features of the glyco-undecapeptide were determined by circular dichroism measurements both in water and in 98% trifluoroethanol. Results of biological assays will be published elsewhere.
2. Practical synthesis of the 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucosides of Fmoc-serine and Fmoc-threonine and their benzyl esters
K P Ravindranathan Kartha, Robert A Field, Shona L Scheuerl, Ivone Carvalho Carbohydr Res . 2003 May 1;338(10):1039-43. doi: 10.1016/s0008-6215(03)00071-5.
Mercuric bromide-promoted glycosylation of Fmoc-Ser-OBn and Fmoc-Thr-OBn with 2-acetamido-2-deoxy-3,4,6-tri-O-acetyl-alpha-D-glucopyranosyl chloride in refluxing 1,2-dichloroethane gave the corresponding beta-glycosides in good yields (64 and 62%, respectively). Direct coupling of the commercially available Fmoc-Ser-OH and Fmoc-Thr-OH carboxylic acids under similar conditions gave the corresponding beta-glycosides, possessing free carboxyl groups, in moderate yields (50 and 40%, respectively).
