ChemInform Abstract: AN APPROACH TO THE SYNTHESIS OF LIPONUCLEOTIDES

Abstract

Phosphorylierung des Thymidins (Ia) bzw. des Diacylglycerins (Va) mit dem Reagenz (II) gibt die Derivate (Ib) bzw. (Vb), die unmittelbar mit dem Alkohol (III) bzw. mit (Ia) umgesetzt werden.

Efficient Iterative Synthesis of O‐Acetylated Tri‐ to Pentadecasaccharides Related to the Lipopolysaccharide of Shigella flexneri Type 3 a through Di‐ and Trisaccharide Glycosyl Donors

“…Taking into account previous achievements in the use of trichloroacetimidate donors for the convergent synthesis of higher oligosaccharides, trisaccharide 11 was transformed into BCD trichloroacetimidate 14 in two steps (Scheme ). Thus, iridium‐catalyzed isomerization of the allyl moiety into the corresponding propen‐1‐yl group, followed by hydrolysis in the presence of buffered iodine/H 2 O, converted allyl glycoside 11 into hemiacetal 13 (82 %). This one‐pot procedure was adapted from a published protocol by Hecker et al., wherein a similar acid‐labile protecting group was present on the glucosamine residue.…”

Detailed Investigation of the Immunodominant Role of O‐Antigen Stoichiometric O‐Acetylation as Revealed by Chemical Synthesis, Immunochemistry, Solution Conformation and STD‐NMR Spectroscopy for Shigella flexneri 3a

“…Controlled base‐mediated transesterification of the fully protected 3‐ O ‐acetyl precursor 18 by using K 2 CO 3 in methanol provided the alcohol 19 (94 %), and the levulinyl group was installed [LevOH, N , N ′‐dicyclohexylcarbodiimide (DCC), 4‐dimethylaminopyridine (DMAP)] to furnish the intermediate 20 (98 %). Following conventional iridium(I)‐catalyzed allyl isomerization, the anomeric propenyl ether was cleaved when treated with aqueous iodine in the presence of NaHCO 3 to prevent isopropylidene loss . The crude material was directly converted to the trichloroacetimidate 8 (84 % from compound 20 ) to avoid extensive degradation .…”

Synthesis of Two Tetra‐ and Four Pentasaccharide Fragments of Shigella flexneri Serotypes 3a and X O‐Antigens from a Common Tetrasaccharide Intermediate

“…The fully protected disaccharide 15 was isolated in an excellent 95 % yield. Allyl glycoside 15 was then converted to hemiacetal 16 (92 %) following a two‐step selective deallylation procedure involving: (i) the isomerisation of the allyl ether into the corresponding prop‐1‐enyl ether with a cationic iridium complex31 and (ii) subsequent iodine‐mediated hydrolysis 32. Finally, the EA disaccharide donor 7 was obtained as an anomeric mixture in 97 % yield by reacting hemiacetal 16 with trichloroacetonitrile with a catalytic amount of DBU.…”