Intramolecular 1,8- versus 1,6-hydrogen atom transfer between pyranose units in a (1-->4)-disaccharide model promoted by alkoxyl radicals. Conformational and stereochemical requirements |
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Authors: | Martín Angeles Pérez-Martín Inés Quintanal Luis M Suarez Ernesto |
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Affiliation: | Instituto de Productos Naturales y Agrobiología del C.S.I.C., Carretera de La Esperanza 3, 38206 La Laguna, Tenerife, Spain. |
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Abstract: | [reaction: see text] The stereochemical and conformational factors controlling the intramolecular hydrogen atom transfer (HAT) reaction between the two pyranose units in a (1-->4)-disaccharide when promoted by a primary 6-O-yl radical are studied. Models with alpha-d-Glcp-(1-->4)-beta-d-Glcp or alpha-l-Rhamp-(1-->4)-alpha-d-Galp skeletons lead exclusively to the abstraction of H-C-5' and the formation, through a nine-membered transition state, of a 1,3,5-trioxocane ring system in a stable boat-chair conformation. Notwithstanding, derivatives of alpha-l-Rhamp-(1-->4)-alpha-d-Glcp abstract exclusively H-C-1' through a seven-membered transition state and therefore lead to an interglycosidic spiro ortho ester. |
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