1. Synthesis of O-glycosylated tuftsins by utilizing threonine derivatives containing an unprotected monosaccharide moiety
F Filira, L Biondi, F Cavaggion, B Scolaro, R Rocchi Int J Pept Protein Res. 1990 Jul;36(1):86-96. doi: 10.1111/j.1399-3011.1990.tb00086.x.
Synthesis is described of four tuftsin derivatives containing a D-glucopyranosyl or a D-galactopyranosyl unit covalently linked to the hydroxy side chain function of the threonine residue through either an alpha or beta O-glycosidic linkage. Fmoc-threonine derivatives containing the suitable unprotected sugar were used for incorporating the O-glycosylated amino acid residue. Z-Thr[alpha-Glc(OBzl)4]-OBzl and Z-Thr[alpha-Gal(OBzl)4]-OBzl were prepared from the tetra-O-benzylated sugar and Z-Thr-OBzl by the trichloroacetimidate method in the presence of trimethylsilyl trifluoromethane sulfonate. The alpha glycosylated threonine derivatives were converted into Fmoc-Thr(alpha-Glc)-OH and Fmoc-Thr(alpha-Gal)-OH by catalytic hydrogenation followed by acylation with Fmoc-OSu. beta-Glucosylation and beta-galactosylation of threonine were carried out by reacting the proper per-O-acetylated sugar with Z-Thr-OBzl and boron trifluoride ethyl etherate in dichloromethane. Catalytic hydrogenation of the beta-O-glycosylated threonine derivatives followed by acylation with Fmoc-OSu and deacetylation with methanolic hydrazine yielded Fmoc-Thr(beta-Glc)-OH and Fmoc-Thr(beta-Gal)-OH, respectively. The O-glycosylated threonine derivatives were then reacted with H-Lys(Z)-Pro-Arg(NO2)-OBzl in the presence of DCC and HOBt and the resulting glycosylated tuftsin derivatives were fully deblocked by catalytic hydrogenation, purified by HPLC, and characterized by optical rotation, amino acid analysis, and 1H NMR. The beta-galactosylated tuftsin was also prepared by the continuous flow solid phase procedure.
2. Rhodium(I)-Catalyzed
B Witulski, T Stengel Angew Chem Int Ed Engl. 1999 Aug;38(16):2426-2430.
The regiospecific introduction of substituents into the 4-position of 2,3-dihydroindoles (indolines), which is significant for the synthesis of various natural products and pharmaceuticals, was achieved by rhodium(I)-catalyzed cyclotrimerizations of 1 with acetylene to give 2. Up to four substituents can be introduced simultaneously into the indoline core by using this novel strategy. R=OH, OBzl, Otetrahydropyranyl, NHSO(2)C(6)H(4)CH(3); Ts=H(3)CC(6)H(4)SO(2).
3. Amino acids and peptides. XVIII. Dipeptide formation during the synthesis of Z-Asp(OBzl)-OH
S Iguchi, K Kawasaki, Y Okada Int J Pept Protein Res. 1987 Nov;30(5):695-700. doi: 10.1111/j.1399-3011.1987.tb03382.x.
During the benzyloxycarbonylation of H-Asp(OBzl)-OH by the Schotten-Bauman reaction with benzyloxycarbonyl chloride in the presence of NaHCO3 or Na2CO3, besides Z-Asp(OBzl)-OH, Z-Asp(OBzl)-Asp(OBzl)-OH was formed as side product, although the extent of the dipeptide formation differed depending on the base used (10% and 20% respectively). It was found that melting point, rotation value and Rf values upon thin-layer chromatography of Z-Asp(OBzl)-Asp(OBzl)-OH were quite similar to those of Z-Asp(OBzl)-OH.
