Synthesis Of The Exopolysaccharide From Cryptococcus Neoformans Serotype D

In the past few decades, there has been a sharp increase in the number of deep fungalinfections for a variety of reasons that include those individuals with immunecompromisedhosts, such as patients undergoing anticancer chemotherapy or organ transplantion andpatients with AIDS. Additionally, the widespread use of broad-spectrum antibacterial drugs,predominantly in hospitals, has resulted in an increase in the prevalence of patients at riskfor fungal infections. Cyrptococcus neoformans is a common pathogenic bacteria, recentstudies found that the Cryptococcus neoformans has a polysaccharide capsule withfunctional relate to its toxicity and infectivity. There are two types of polysaccharidecapsule, of which the major is glucuronoxylomannan (GXM). GXM is a copolymer of upto six different repeating units that consist mostly of a linear (1→3)-mannan trisaccharidewith side groups consisting of a β(1→2)-glucopyranosyluronic acid and β(1→2) andβ(1→4)-xylopyranosyl. D-serotypes xylose and mannose ratio is1:3, while the ratio of theC-serotype4:3. The mannan backbone of GXM is modified by acetyl groups and it has asignificance antigenic characteristics. The antigenic properties of GXM has become animportant connection fragments of Cryptococcus neoformans vaccine research. Apolysaccharide coupled to a protein carrier has a high immunogenicity and can be repeatedto induce high titers of serum after immunization.Carbohydrates，the vital component of organism, mainly exists on the cell surface informs of glycoproteins and glycolipids. It is not only the important source of energy andcarbon, but also plays key roles in the aspects of cell adhesion, phagotrophy and signaltransmission.β-D-Xylp-(1→2)-α-D-Manp-(1→3)-[β-D-GlcpA-(1→2)]-α-D-Manp-(1→3)-α-D-Ma-np, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar Dwas synthesized as its4-Methoxyphenyl glycoside. Thus,3-O-selective acetylation of4-Methoxyphenyl4,6-di-O-benzoyl--D-mannopyranoside afforded Acceptor I, AcceptorII, and then respectively glycosylation of Acceptor I with2,3,4-tri-O-benzoyl-D-xylopyranosyl trichloroacetimidate and Methyl2,3,4-tri-O-benzoyl-D-gluco pyranosyl-uronate trichloroacetimidate furnished the β-(1→2)-linked disaccharide16and18.Followed by oxidative cleavage of1-OMP and subsequent trichloroacetimidate formationgave the β-(1→2)-linked disaccharide donor17, Selective3-O-deacetylation gave theβ-(1→2)-linked disaccharide acceptor19. Condensation of17with19and subsequent oxidative cleavage of1-OMP, and trichloroacetimidate formation produced the tetra-saccharide donor21. Coupling of Acceptor II with the tetrasaccharide trichloroacetimidate21and get the target pentasaccharide. Their immunogenicity of the oligosaccharide can beimproved by coupling them to peptides fragment on GPI-CWPs, which are closely relatedto the growth, adhesion, invasion and virulence of C. neoformans. Their structures wereconfirmed by1HNMR,13CNMR and HR-QTOF-MS. The ability of the synthetic oligo-saccharide vaccines to elicit antibody to GXM was measured by ELISA. In summary, thisstudy has great signifycance for the Cryptococcus neoformans vaccine research andrepresents a potential synthetic oligosaccharide vaccine against this fungal pathogen.