The recently described [Attolino, E.; Bonaccorsi, F.; Catelani, G.; D’Andrea, F. Carbohydr. Res. 2008, 343, 2545–2556.] beta-D-MaNAcp-(1→4)-beta-D-Glcp thiophenyl glycosyl donor 3 was used in a-glycosylation reactions of OH-2 and OH-3 of the suitably protected p-MeO-benzyl alfa-L-rhamnopyranoside acceptors 7 and 8. Glycosylation of the axial OH-2 of 7 took place in high yield (76%) and with acceptable stereoselectivity(alfa/beta = 3.4) leading to the protected trisaccharide alfa-11, corresponding to the repeating unit of Streptococcus pneumoniae 19F. The same reaction on equatorial OH-3 of acceptor 8 gave the trisaccharide a-15, a constituent of the repeating unit of S. pneumoniae 19A, but in lower yield (41%) and without stereoselection (alfa/beta = 1:1.3). Utilizing the introduced orthogonal protection of OH-1 and OH-400 , the trisaccharide alfa-11 was transformed into a trisaccharide building block suitable for the synthesis of its phosphorylated oligomers
A new route for the synthesis of Streptococcus Pneumoniae 19F and 19A capsular polysaccharide fragments avoiding the beta-mannosamine glycosylation step
CATELANI, GIORGIO;
2009-01-01
Abstract
The recently described [Attolino, E.; Bonaccorsi, F.; Catelani, G.; D’Andrea, F. Carbohydr. Res. 2008, 343, 2545–2556.] beta-D-MaNAcp-(1→4)-beta-D-Glcp thiophenyl glycosyl donor 3 was used in a-glycosylation reactions of OH-2 and OH-3 of the suitably protected p-MeO-benzyl alfa-L-rhamnopyranoside acceptors 7 and 8. Glycosylation of the axial OH-2 of 7 took place in high yield (76%) and with acceptable stereoselectivity(alfa/beta = 3.4) leading to the protected trisaccharide alfa-11, corresponding to the repeating unit of Streptococcus pneumoniae 19F. The same reaction on equatorial OH-3 of acceptor 8 gave the trisaccharide a-15, a constituent of the repeating unit of S. pneumoniae 19A, but in lower yield (41%) and without stereoselection (alfa/beta = 1:1.3). Utilizing the introduced orthogonal protection of OH-1 and OH-400 , the trisaccharide alfa-11 was transformed into a trisaccharide building block suitable for the synthesis of its phosphorylated oligomersI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.