STEREOSELECTIVE SYNTHESIS OF A TETRAMERIC FRAGMENT OF STREPTOCOCCUS-PNEUMONIAE TYPE-1 CONTAINING AN ALPHA-LINKED ACETAMIDO-4-AMINO-2,4,6-TRIDEOXY-D-GALACTOPYRANOSE (SUGP) UNIT

Block condensation of fully protected donor ethyl (5-->P-->6)-2,3,4-tr i-O-benzoyl-1-thio-beta-D-Glcp (2), having a (5-->6)-phosphotriester u nion between the ribitol and the glucopyranosyl moieties, with the fre e 3'-OH group in the acceptor methyl alpha-D-Galp)-3,6-di-O-benzyl-2-d eoxy-alpha-D-Galp (3), under the agency of N-iodosuccinimide and trifl ic acid, gave the fully protected tetrameric fragment 22. Elimination of the 2-cyanoethyl group from the phosphotriester and subsequent debe nzoylation, followed by hydrogenolysis of the benzyl and benzyloxycarb onyl groups provided the target tetramer methyl Glcp-beta(1-->3)-Sugp- alpha(1-->4)-alpha-D-GalpNAc (1).