[en] A new spin trap, the 5-(diethoxyphosphorylmethyl)-5-methyl-4,5-dihydro-3H-pyrrole N-oxide (3),
is prepared through a four-step synthetic route. The in vitro spin trapping properties of 3 have been investigated and the hydroxyl and superoxide spin adducts characterised. The persistence of the superoxide spin adduct obtained with 3 is compared with those of the analogues obtained with DEPMPO [5-(diethoxyphosphoryl)-5-methyl-4,5-dihydro-3H-pyrrole N-oxide] and DMPO in both phosphate buffer and pyridine. In 0.1 M phosphate buffer at pH 7.0, the HOO-3? adduct is found to be 2.8 times more persistent than HOO-DMPO?, but 5.7 times less than HOO-DEPMPO?. In phosphate buffer, HOO-3? decomposes to give HO-3?. The stereoselectivity of the addition of free radicals on 3 is generally poor, and mixtures of diastereomers have been observed by EPR. The overall spin trapping behaviour of nitrone 3 is more similar to that of DMPO than that of DEPMPO.