Functionalization of mannans from pathogenic yeasts by different means of oxidations—preparation of precursors for conjugation reactions with respect to preservation of immunological properties

Three different reagents (sodium periodate, Dess–Martin periodinane (DMP), 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/hypochlorite/bromide) were used to prepare oxidized forms of mannans from the four pathogenic yeasts of Candida genus (Candida albicans, Candida tropicalis, Candida glabrata, Candida parapsilosis) in order to prepare glycoconjugate vaccine precursors suitable for reductive amination reactions. A combination of NMR, IR, potentiometric titration, Park–Johnson colorimetric assay and size exclusion chromatography was applied for physicochemical characterization of the oxidized mannans. Correlation between molecular weight of periodate, DMP and TEMPO-mediated oxidized mannans and branching frequency as a characteristic structural feature of original cell wall mannans was found. It indicates that higher branching frequency of original mannan used in the reaction, lesser molecular weight decrease of oxidized mannan measured. This dependence determined by SEC upon oxidation agent can be expressed by following relationship: (TEMPO)>original>DMP≫periodate. Immunological characteristics relevant to applications in vaccine technology (i.e. preservation of antigenic structural properties of polysaccharides) were analyzed in detail. It was revealed, that modification of immunological properties or damage of relevant epitopes due to structural changes via DMP and TEMPO-mediated oxidation can be excluded.