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The tetrasaccharide (2- O -methyl-4-(3-hydroxy-3-methylbutamido)-4,6-dideoxy-α-d-glucopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→2)-l-rhamnopyranose) from the major exosporium protein (BclA) of Bacillus anthracis has been proposed as a target for development of diagnostics and immune therapy or prophylaxis. While the immunodominant character of the anthrose residue has been previously elucidated, the role of the stereochemical configuration of the downstream rhamnose is unknown. Because the linkage of this residue to the GlcNAc bridging the glycan and the protein is lost during isolation of the tetrasaccharide, its α- and β-glycoforms have been synthesized. Herein, we prepared neoglycoconjugates from a series of fragments of the tetrasaccharide, including the complete α- and β-tetrasaccharide glycoforms, a 2-demethoxylated version of the α-tetrasaccharide, and the α- and β-trirhamnosides and CRM 197 . By immunization of mice, we showed that the anti α- and β-tetrasaccharide serum equally recognized both glycoforms. In contrast the sera produced following immunization with the α- and β-trirhamnoside fragments exhibited higher recognition for their own antigens than for their anomeric counterparts. The anti α- and β-tetrasaccharide sera recognized Sterne spores in a comparable fashion. ΔBclA spores not expressing the major exosporium protein were also recognized by the same sera, while mutants that produced the carbohydrate antigen with deletion of either rhamnose or anthrose were not. The tetrasaccharide could, therefore, be expressed in proteins other than BlcA. This work proves that α- and β-tetrasaccharide are equally potent immunogens.

Methods for the immunological detection of Bacillus anthracis in various environmental samples and the discrimination of B. anthracis from other members of the B. cereus group are not yet well established. To generate specific discriminating antibodies, we immunized rabbits, mice, and chickens with inactivated B. anthracis spores and, additionally, immunized rabbits and mice with the tetrasaccharide beta-Ant-(1-->3)-alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->2)-L-Rhap. It is a constituent of the exosporium glycoprotein BclA and contains the newly discovered sugar anthrose 2-O-methyl-4-(3-hydroxy-3-methylbutamido)-4,6-dideoxy-beta-D-glucose. The BclA protein is a major component of the exosporium of B. anthracis spores and is decorated by the tetrasaccharide indicated above. The anthrose-containing tetrasaccharide chain seems to be highly specific for B. anthracis, which makes it a key biomarker for the detection of these spores. The different immunizations led to anthrose-reactive polyclonal and monoclonal antibodies which were analyzed by various methods to characterize their ability to discriminate between B. anthracis and other Bacillus spp. Multiple applications, such as enzyme-linked immunosorbent assay, indirect immunofluorescence assay, and electron microscopy, revealed the specificities of the polyclonal and monoclonal antibodies generated for B. anthracis spore detection. All polyclonal antibodies were able to correctly identify the B. anthracis strains tested and showed only minimal cross-reactivities with other Bacillus strains. Moreover, the antibodies generated proved functional in a new capture assay for B. anthracis spores and could therefore be useful for the detection of spores in complex samples.

We developed a microarray platform by immobilizing bacterial 'signature' carbohydrates onto epoxide modified glass slides. The carbohydrate microarray platform was probed with sera from non-melioidosis and melioidosis (Burkholderia pseudomallei) individuals. The platform was also probed with sera from rabbits vaccinated with Bacillus anthracis spores and Francisella tularensis bacteria. By employing this microarray platform, we were able to detect and differentiate B. pseudomallei, B. anthracis and F. tularensis antibodies in infected patients, and infected or vaccinated animals. These antibodies were absent in the sera of naïve test subjects. The advantages of the carbohydrate microarray technology over the traditional indirect hemagglutination and microagglutination tests for the serodiagnosis of melioidosis and tularemia are discussed. Furthermore, this array is a multiplex carbohydrate microarray for the detection of all three biothreat bacterial infections including melioidosis, anthrax and tularemia with one, multivalent device. The implication is that this technology could be expanded to include a wide array of infectious and biothreat agents.

The known methyl 2-O-acetyl-3,4-di-O-benzyl-1-thio-alpha-L-rhamnopyranoside (3) was converted to the corresponding 5-methoxycarbonylpentyl glycoside 4 which was deacetylated. The product 5 was used as the initial glycosyl acceptor to construct two trirhamnoside glycosyl acceptors having HO-3(III) flanked by either benzoyl or benzyl groups, compounds 10 and 29, respectively [fully protected, except HO-3(III), alpha-L-Rha-(1-->3)-alpha-L-Rha-(1-->2)-alpha-L-Rha-1-O-(CH2)5COOCH3]. When these were glycosylated with ethyl 4-azido-3-O-benzyl-4,6-dideoxy-2-O-bromoacetyl-1-thio-beta-D-glucopyranoside (18), only the benzylated glycosyl acceptor 29 gave good yield of the desired tetrasaccharide 30. The alpha- and beta-linked products, together with the corresponding orthoester 23, were formed in almost equal amount when glycosylation of 10 was performed with the glycosyl donor carrying the 2-O-bromoacetyl protecting group. Deprotection at O-2 of 30, followed by further functionalization of the molecule and global deprotection, gave the 5-methoxycarbonylpentyl glycoside of the title tetrasaccharide, beta-Ant-(1-->3)-alpha-L-Rha-(1-->3)-alpha-L-Rha-(1-->2)-alpha-L-Rha (35). Except for differences due to presence of the anomeric 5-methoxycarbonylpentyl group, the fully assigned NMR spectra of glycoside 35 were found to be virtually identical to those reported for the parent tetrasaccharide isolated from Bacillus anthracis exosporium, thus proving the correct structure assigned to the naturally occurring substance. All theoretically possible structural fragments of 35, as well as analog of 35 lacking the 2-O-methyl group at the terminal 4,6-dideoxyglucosyl residue, compound 40, were also synthesized. Tetrasaccharide 35, its beta-linked and non-methylated analogs 2 and 40, respectively, as well as the trirhamnoside fragment of 35, glycoside 12, were further functionalized and conjugated to BSA using squaric acid chemistry, to give neoglycoconjugates with a predetermined carbohydrate-protein ratio of approximately 3 and approximately 6.

Using photogenerated glycan arrays, we characterized a large panel of synthetic carbohydrates for their antigenic reactivities with pathogen-specific antibodies. We discovered that rabbit IgG antibodies elicited by Bacillus anthracis spores specifically recognize a tetrasaccharide chain that decorates the outermost surfaces of the B. anthracis exosporium. Since this sugar moiety is highly specific for the spores of B. anthracis, it appears to be a key biomarker for detection of B. anthracis spores and development of novel vaccines that target anthrax spores.

An alpha-glycoside of the tetrasaccharide sequence beta-Ant-(1-->3)-alpha-l-Rhap-(1-->3)-alpha-l-Rhap-(1-->2)-alpha-l-Rhap whose aglycon allows conjugation to suitable carriers was synthesized. The NMR characteristics of the compound are virtually identical with those of the alpha-anomer of the tetrasaccharide isolated from the major glycoprotein of the Bacillus anthracis exosporium. Thus, the correct structure of the natural product has been proven by chemical synthesis.

The beta glycoside of the tetrasaccharide sequence beta-Ant-(1-->3)-alpha-l-Rhap-(1-->3)-alpha-l-Rhap-(1-->2)-l-Rhap, whose aglycon allows conjugation to proteins, was synthesized for the first time. A stepwise synthetic approach was applied with thioglycosides as glycosyl donors, and the beta anomer of the compound was obtained equipped with a spacer group whose further transformation allows conjugation to suitable carriers. To synthesize the beta-anthrosyl linkage with high stereoselectivity, a linker-equipped rhamnotriose derivative was glycosylated with ethyl 4-azido-3-O-benzyl-2-O-bromoacetyl-4,6-dideoxy-1-thio-beta-d-glucopyranoside. Further functionalization of the tetrasaccharide thus obtained, followed by deprotection, gave the target substance.