Specific carbohydrate radicals and spin trapping
γ-irradiation of solid sugars produces a large number of radicals, detection of which is possible by e.s.r. However, unambiguous interpretation of these e.s.r. signals is extremely difficult either by direct measurement or by spin trapping/hplc methods. The present study set out to prepare specific sugar spin adducts and to compare their e.s.r. spectra with those obtained by spin trapping radicals present in γ-irradiated solid sugars. In this way unambigous identification of the spin adducts may be achieved. Most specific carbohydrate radicals have previously been prepared using tri-alkyl tin radicals and protected halo-sugars in organic solution. To impart water solubility to the tin radicals, the preparation of hexa(3-pyridyl-1'-oxide)ditin was attempted and resulted in the synthesis of a new tetra(3-pyridyl)tin. Model halogeno compounds on reaction with the carbon dioxide radical anion CO2.-, gave radicals which were trapped with 2-methy-2-nitrosopropane (MNP)) and the adducts identified by e.s.r. Both carboxylic acids, and ketones with an adjacent halogen, underwent reductive elimination to form on spin trapping, the dehalogenated spin adduct. Where the halogen, X = C1,Br is adjacent to a primary or secondary alcohol, oxidation occurred before dehalogenation. However, where X = I, oxidation did not occur and the corresponding deioinated radical was obtained. Iodo sugars were synthesised and selectively deiodinated using CO2.- to give specific carbohydrate radicals that were trapped with MNP and the adducts identified by e.s.r. New b N-t-butyl carbohydrate nitrones were prepared by reaction of the corresponding aldehyde and N-t-butylhydroxylamine. Derivatives were prepared by [2+3] cycloaddition reactions with styrene and dimethylacetylene dicarboxylate. Using these nitrones as spin traps, several simple radicals were trapped to give the corresponding spin adduct. The e.s.r. spectra obtained from the hydroxyl radical derived spin adducts showed small aH coupling constants in contrast to those already published for similar adducts. This is explained in terms of hydrogen bonding which fixes the conformations of these spin adducts.