The beta- pyranose form, ( III), of 3- deoxy- D- ribo- hexose ( 3- deoxy- D- glucose), C6H12O5, crystallizes from water at 298 K in a slightly distorted C-4(1) chair conformation. Structural analyses of ( III), beta- D- glucopyranose, ( IV), and 2- deoxy- beta- D-arabinohexopyranose ( 2- deoxy- beta- D- glucopyranose), ( V), show significantly different C - O bond torsions involving the anomeric carbon, with the H - C - O - H torsion angle approaching an eclipsed conformation in ( III) (. 10.9 degrees) compared with 32.8 and 32.5 degrees in ( IV) and ( V), respectively. Ring carbon deoxygenation significantly affects the endo- and exocyclic C - C and C - O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species ( III) and ( V) compared with ( IV). These structural changes are attributed to differences in exocyclic C - O bond conformations and/ or hydrogenbonding patterns superimposed on the direct ( intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in ( III) ( gt) differs from that observed in ( IV) and ( V) ( gg).
Complexes of Borane and N-Heterocyclic Carbenes: A New Class of Radical Hydrogen Atom Donor
作者:Shau-Hua Ueng、Malika Makhlouf Brahmi、Étienne Derat、Louis Fensterbank、Emmanuel Lacôte、Max Malacria、Dennis P. Curran
DOI:10.1021/ja804150k
日期:2008.8.1
Calculations suggest that complexes of borane with N-heterocyclic carbenes (NHC) have B-H bond dissocation energies more then 20 Kcal/mol less than free borane, diborane, borane-THF, and related complexes. Values are in the range of popular radical hydrogen atom donors like tin hydrides (70-80 Kcal/mol). The resulting prediction that NHC borane complexes could be used as radical hydrogen atom donors was verified by radical deoxygenations of xanthates by using either AIBN or triethylborane as initiator.
Novel radical chain reactions based on O-alkyl tin dithiocarbonates
作者:Jean Boivin、Jose Camara、Samir Z. Zard
DOI:10.1021/ja00046a045
日期:1992.9
Tetrahydrothiophene nucleosides as potential anti-HIV agents
作者:Martin F. Jones、Stewart A. Noble、Colin A. Robertson、Richard Storer
DOI:10.1016/0040-4039(91)80867-6
日期:1991.1
A series of novel tetrahydrothiophenenucleosides have been prepared in homochiral form from D-glucose and assessed as anti-HIVagents in whole cell assay.
The beta- pyranose form, ( III), of 3- deoxy- D- ribo- hexose ( 3- deoxy- D- glucose), C6H12O5, crystallizes from water at 298 K in a slightly distorted C-4(1) chair conformation. Structural analyses of ( III), beta- D- glucopyranose, ( IV), and 2- deoxy- beta- D-arabinohexopyranose ( 2- deoxy- beta- D- glucopyranose), ( V), show significantly different C - O bond torsions involving the anomeric carbon, with the H - C - O - H torsion angle approaching an eclipsed conformation in ( III) (. 10.9 degrees) compared with 32.8 and 32.5 degrees in ( IV) and ( V), respectively. Ring carbon deoxygenation significantly affects the endo- and exocyclic C - C and C - O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species ( III) and ( V) compared with ( IV). These structural changes are attributed to differences in exocyclic C - O bond conformations and/ or hydrogenbonding patterns superimposed on the direct ( intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in ( III) ( gt) differs from that observed in ( IV) and ( V) ( gg).