Q1. What contributions have the authors mentioned in the paper "Intramolecular 1,8-versus 1,6-hydrogen atom transfer between pyranose units in a (1f4)-disaccharide model promoted by alkoxyl radicals. conformational and stereochemical requirements" ?
The stereochemical and conformational factors controlling the intramolecular hydrogen atom transfer ( HAT ) reaction between the two pyranose units in a ( 1f4 ) -disaccharide whenpromotedbyaprimary6-O-yl radicalarestudied. In a previous paper from this laboratory, the authors described a most unusual 1,8-hydrogen atom transfer ( HAT ) between the two glucopyranose units of a R-D-Glcp- ( 1f4 ) -§-D-Glcp disaccharide ( D-maltose ) ( 1 ) through a nine-membered transition state. The authors therefore analyzed the conformation of the ring for all 16 possible disaccharide diastereoisomers of the four chiral centers involved in the cyclization step ( C-5, C-1, C-4, and C-5 ). Nevertheless, the authors are aware that the cyclization step may also be influenced by the nature and stereochemistry of all the substituents of the sugar molecule, not only by the stereochemistry of the trioxocane ring carbons ( C-5, C-1, C-4, and C-5 ), and that generalizations are difficult at this stage of the research. This work was supportedby Research programs CTQ2004-06381/BQU and CTQ2004-02367/BQU of the Ministerio de Educacio ́n y Ciencia, Spain, cofinanced by the Fondo Europeo de Desarrollo Regional ( FEDER ). Furthermore, the observed coupling constants for the hydrogens at C-4 and C-6 ( J4,5 ) 9. 5 Hz, J5,6e ) 5. 1 Hz, and J5,6a ) 10. 4 Hz ) are consistent with a chair conformation for the 1,3-dioxane ring.