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.
[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.
Martín
Angeles
A
Instituto de Productos Naturales y Agrobiología del C.S.I.C., Carretera de La Esperanza 3, 38206 La Laguna, Tenerife, Spain.
Pérez-Martín
Inés
I
Quintanal
Luis M
LM
Suarez
Ernesto
E
D000438:Alcohols / Q000737:chemistry*; D004187:Disaccharides / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry*; D008320:Maltose / Q000737:chemistry; D008954:Models, Biological; D008968:Molecular Conformation; D013237:Stereoisomerism
D000438:Alcohols; D004187:Disaccharides; D005609:Free Radicals; C059688:alkoxyl radical; D008320:Maltose; D006859:Hydrogen