New mono- and difunctionalized 2,2,5,5-tetramethylpyrrolidine- and Δ3-pyrroline-1-oxyl nitroxide spin labels

Abstract

Several new nitroxide spin labels have been prepared. Nitroxide mesylate 5 and p-hydroxyacetophenone gave 6 which was selectively brominated with cupric bromide to give the alkylating agent 7. The more water soluble phenacyl bromide analogue 17 was prepared either via the route 8 → 11 → 17 or else via the route 15 → 16 → 11 → 17. Preliminary results indicate that toward aconitase, nitroxide alkylating agent 17 behaves similarly to phenacyl bromide. Several new difunctional nitroxides were prepared with an eye toward application as saturation transfer esr spin labels. Conjugate addition of HCN to 11 gave 18, condensation of which with p-azidobenzaldehyde gave photolabile 19. Azide 20 could similarly be prepared directly from 11. Aldehyde 15 underwent condensation with p-azidoacetophenone to give azide 21. This substance was allowed to react with hemoglobin. Upon photolysis the esr spectral mobile component was substantially reduced, suggesting covalent attachment at more than one site. Conjugate addition of HCN to 23 gave a mixture of cis, trans isomers 24 and 25; the structure of 25 was established by X-ray crystallographic analysis to be the trans isomer. Conjugate addition of ethyl thioglycolate to 15 led to heterocycles 29–34.