CONFORMATIONAL STUDY OF A SUGAR NITROXYL FREE-RADICAL

Ethyl2,3-dideoxy-2-isopropylamino-alpha-D-arabino-hexopyranoside N-oxyl and its 2'-d analogue have been studied by variable-temperature e.s.r. spectroscopy. At low temperature, two frozen conformers (5,a(H-2)) = 15.5 G; and 6, a(H-2) = 1.8 G) were found. Semi-empirical quantum mechanics and molecular mechanics, using specially developed parameters for hydroxylamines and nitroxyls, helped to assign an almost eclipsed geometry (O-N-C-2-C-1 approximately 10-degrees) to 5 and a compromise between a staggered and the nearest eclipsed conformation (O-N-C-2-C-1 approximately 80-degrees) to 6.