Assignment of the 1H, 13C and 15N resonances in cyclodextrin nitrates by 2D NMR and the determination of the regioselectivity of the hydroxylamine-induced denitration reactions

Hexakis(2,3,6-tri-O-nitro)-α-cyclodextrin and heptakis(2,3,6-tri-O-nitro)-β-cyclodextrin were prepared and the complete assignment of the 1H, 13C and 15N resonance signals in each case was achieved using homonuclear shift correlation experiments, one-bond 13C1H and three-bond 15NOC1H heteronuclear shift correlation measurements. The denitration of these cyclodextrin nitrates by hydroxylamine in pyridine was investigated to study its selectivity in preparing partially nitrated derivatives of these cyclodextrins. The sites of denitration were determined in each case using 13C and 15N NMR and the products were completely characterized. The results indicate that denitration of these cyclodextrin nitrates is a highly regiospecific reaction occurring at the 2-position only and giving rise to hexakis(3,6-di-O-nitro)-α-cyclodextrin and heptakis(3,6-di-O-nitro)-β-cyclodextrin, respectively.