A concise synthesis of two isomeric pentasaccharides, the O repeat units from the lipopolysaccharides of P. syringae pv. porri NCPPB 3364 T and NCPPB 3365

Abstract

A concise synthesis of two isomeric pentasaccharides, α- l-Rha p-(1 → 2)-α- l-Rha p-(1 → 3)-α- l-Rha p-(1 → 3)-[β- d-Glc pNAc-(1 → 2)]-α- l-Rha p ( A ) and α- l-Rha p-(1 → 2)-α- l-Rha p-(1 → 3)-[β- d-Glc pNAc-(1 → 2)]-α- l-Rha p-(1 → 3)-α- l-Rha p ( B ), the O repeats from the lipopolysaccharides of Pseudonomonas syringae pv. porri NCPPB 3364 T and 3365 was achieved via assembly of the building blocks, allyl 3,4-di- O-benzoyl-α- l-rhamnopyranoside ( 1 ), 2,3,4-tri- O-benzoyl-α- l-rhamnopyranosyl trichloroacetimidate ( 2 ), allyl 4- O-benzoyl-3- O-chloroacetyl-α- l-rhamnopyranoside ( 6 ), 3,4,6-tri- O-acetyl-2-deoxy-2-phthalimido-β- d-glucopyranosyl trichloroacetimidate ( 7 ), and allyl 2,4-di- O-benzoyl-α- l-rhamnopyranoside ( 10 ). Coupling of 1 with 2 followed by deallylation and trichloroacetimidate formation gave the disaccharide donor 5 , while condensation of 6 with 7 , followed by dechloroacetylation, offered the disaccharide acceptor 9 . Then, 5 was coupled with 10 to obtain the trisaccharide 11 , and subsequent deallylation and trichloroacetimidate formation furnished the trisaccharide donor 13 . Coupling of 9 with 13 , followed by deprotection, afforded pentasaccharide 19 , while condensation of 9 with 5 , followed by deallylation and trichloroacetimidate formation, gave the tetrasaccharide donor 16 , whose coupling with 10 and subsequent deprotection yielded another pentasaccharide 22 .