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o‑Xylylene Protecting Group in Carbohydrate Chemistry: Application to the Regioselective Protection of a Single vic-Diol Segment in Cyclodextrins

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posted on 2016-02-19, 22:31 authored by Patricia Balbuena, Rita Gonçalves-Pereira, José L. Jiménez Blanco, M. Isabel García-Moreno, David Lesur, Carmen Ortiz Mellet, José M. García Fernández
A systematic study of the suitability of α,α′-dibromo-o-xylene as a reagent for cyclic o-xylylene protection of vic-diols in different monosaccharide substrates is reported. The installation of this protecting group, formally equivalent to a di-O-benzylation reaction, proceeds with good regioselectivity toward 1,2-trans-diequatorial diol systems in pyranose and furanose rings. Initially, the benzyl ether-type derivative of the more acidic hydroxyl is preferentially formed. Subsequent intramolecular etherification toward the equatorial-oriented vicinal OH is kinetically favored. The methodology has been implemented for the simultaneous protection of the secondary O-2 and O-3 positions of a single d-glucopyranosyl unit in cyclic oligosaccharides of the cyclodextrin (CD) family (cyclomaltohexa-, -hepta-, and -octaose; α, β, and γCD).

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