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In this article, the synthesis of a novel α-phosphorus-containing spin trap DEPPEPO [2-(diethoxyphosphoryl)-2-phenethyl-3,4-dihydro-2H-pyrrole-1-oxide] and the evaluation of its ability to spintrap radicals, especially superoxide and hydroxyl radicals, are described. Single crystal X-ray structure analysis reveals that there exist a lot of intramolecular nonbonded attractive interactions in the molecule. The phenethyl group is located away from the diethoxyphosphoryl group and the nitronyl plane, and only one face of the nitronyl plane is sterically hindered by the oxygen attached to the phosphorus with a double bond. The latter feature is responsible for the stereoselection of the free radical additions on the nitronyl moiety. The ability of DEPPEPO to trap the active superoxide anion radical generated in the HX/XO system and the stability of their spin adduct were investigated with that for DEPMPO. The half-life of DEPPEPO is about 13.4 min, and as a result, the DEPPEPO seems to be a promising lipophilic spin trap, perhaps in both in vitro and in vivo ESR investigation. Because DEPPEPO is a solid compound, it is quite easy to purify by recrystallization and to store the compound even at room temperature. In addition, an obvious increase in lipophilicity for DEPPEPO was found as a contribution of 2-substituted phenethyl. [ABSTRACT FROM AUTHOR]