Browsing by Author "Arco, Susan D."

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alpha-Glycosylation by D-Glucosamine-Derived Donors: Synthesis of Heparosan and Heparin Analogues That Interact with Mycobacterial Heparin-Binding Hemagglutinin
(2012-05-30)
Zulueta, Medel Manuel L.
;
Lin, Shu-Yi
;
Lin, Ya-Ting
;
Huang, Ching-Jui
;
Wang, Chun-Chih
Numerous biomolecules possess alpha-D-glucosamine as structural component. However, chemical glycosylations aimed at this backbone are usually not easily attained without generating the unwanted beta-isomer. We report herein a versatile approach in affording full alpha-stereoselectivity built upon a carefully selected set of orthogonal protecting groups on a D-glucosaminyl donor. The excellent stereoselectivity provided by the protecting group combination was found independent of leaving groups and activators. With the trichloroacetimidate as the optimum donor leaving group, core skeletons of glycosylphosphatidyl inositol anchors, heparosan, heparan sulfate, and heparin were efficiently assembled. The orthogonal protecting groups were successfully manipulated to further carry out the total syntheses of heparosan tri- and pentasaccharides and heparin di-, tetra-, hexa-, and octasaccharide analogues. Using the heparin analogues, heparin-binding hemagglutinin, a virulence factor of Mycobacterium tuberculosis, was found to bind at least six sugar units with the interaction notably being entropically driven.
Deuterium-isotope study on the reductive ring opening of benzylidene acetals
(2011)
Lee, I-Chi
;
Zulueta, Medel Manuel L.
;
Shie, Chi-Rung
;
Arco, Susan D.
;
Hung, Shang-Cheng
Specific deuterated reference compounds were prepared to probe the stereoselectivity of the reductive ring opening of carbohydrate-based benzylidene-type acetals. AlD(3) revealed a retentive stereoselectivity probably through the rare S(N)i (internal nucleophilic substitution) mechanism. An S(N)1-like mechanism occurs in the acid-promoted regioselective BD(3)center dot THF- or Et(3)SiD-reductive ring opening.