Synthesis of some neutral and acidic zona pellucida oligosaccharides.
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Authors
Riley, John George.
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Dalhousie University
Abstract
Description
The glycoproteins constituting the Zona Pellucida (ZP) surrounds the mammalian oocyte and regulates critical steps in the fertilization process. This structure contains several target antigens that have potential use in the development of a contraceptive vaccine. Experimental evidence suggests that the initial interaction between sperm and oocyte is mediated by specific sperm proteins and ZP glycoproteins. This thesis describes the development of methods for the synthesis of neutral and acidic (6-O-sulfate) disaccharides that contain terminal beta-N-acetylglucosamine (GlcNAc) and trisaccharides that contain terminal N-acetyllactosamine (LacNAc) units linked to O-3 of beta-galactose (Gal) units. Efficient syntheses of these molecules with attached 5-azidopentyl linker arms have been developed and are ready for biological assays and conjugation to carrier proteins or peptides.
Several approaches to the formation of the various linkages were evaluated. In the first glycosylation approach, ethyl 6-(2,4,6-tri-O-pivaloyl-beta- D-galactopyranosyloxy) hexanoate (8) was chosen as the glycosyl acceptor. In order to synthesise this molecule, a novel method for the de-O-benzylation of sterically hindered benzyl ethers, using light catalysed alpha-bromination in the presence of aqueous base, was employed. This method was further shown to be applicable to a number of substrates that bear functional groups traditionally used in carbohydrate synthesis. However, due to the unreactivity of 8, a second glycosyl acceptor, 5-azidopentyl 2,4,6-tri-O-benzyl-beta- D-galactopyranoside (48beta), was prepared. This molecule was found to condense with glycosyl donors in good yields to give disaccharide products.
In order to effect the second linkage and form an LacNAc glycosyl donor, the GlcNAc acceptor was protected with an O-6 2-naphthylmethyl ether to give phenyl 2-deoxy-6-O-(2-naphthylmethyl)-2-phthalimido-1-thio-beta- D-glucopyranoside (74). To form the beta(1→4) linkage between Gal and GlcNAc, 74 was regioselectively galactosylated to form the LacNAc glycosyl donor phenyl 2,3,4,6-tetra-O-benzoyl-beta- D-galactopyranosyl-(1→4)-2-deoxy-6-O-(2-naphthylmethyl)-2-phthalimido-1-thio-beta- D-glucopyranoside (76). It was found that compound 76 reacted sluggishly with acceptor 48beta giving a poor yield of the desired trisaccharide (22%), probably because of steric hindrance. (Abstract shortened by UMI.)
Thesis (Ph.D.)--Dalhousie University (Canada), 2003.
Several approaches to the formation of the various linkages were evaluated. In the first glycosylation approach, ethyl 6-(2,4,6-tri-O-pivaloyl-beta- D-galactopyranosyloxy) hexanoate (8) was chosen as the glycosyl acceptor. In order to synthesise this molecule, a novel method for the de-O-benzylation of sterically hindered benzyl ethers, using light catalysed alpha-bromination in the presence of aqueous base, was employed. This method was further shown to be applicable to a number of substrates that bear functional groups traditionally used in carbohydrate synthesis. However, due to the unreactivity of 8, a second glycosyl acceptor, 5-azidopentyl 2,4,6-tri-O-benzyl-beta- D-galactopyranoside (48beta), was prepared. This molecule was found to condense with glycosyl donors in good yields to give disaccharide products.
In order to effect the second linkage and form an LacNAc glycosyl donor, the GlcNAc acceptor was protected with an O-6 2-naphthylmethyl ether to give phenyl 2-deoxy-6-O-(2-naphthylmethyl)-2-phthalimido-1-thio-beta- D-glucopyranoside (74). To form the beta(1→4) linkage between Gal and GlcNAc, 74 was regioselectively galactosylated to form the LacNAc glycosyl donor phenyl 2,3,4,6-tetra-O-benzoyl-beta- D-galactopyranosyl-(1→4)-2-deoxy-6-O-(2-naphthylmethyl)-2-phthalimido-1-thio-beta- D-glucopyranoside (76). It was found that compound 76 reacted sluggishly with acceptor 48beta giving a poor yield of the desired trisaccharide (22%), probably because of steric hindrance. (Abstract shortened by UMI.)
Thesis (Ph.D.)--Dalhousie University (Canada), 2003.
Keywords
Chemistry, Biochemistry., Chemistry, Organic.