EVIDENCE FOR A NOVEL PENTYL RADICAL ADDUCT OF THE CYCLIC NITRONE SPINTRAP MDL-101,002

3,4-Dihydro-3,3-dimethyl-isoquinoline-2-oxide (MDL 101,002) is a confo rmationally constrained cyclic analog of the known spin trap alpha-phe nyl N-tert-butyl nitrone (PEN). Because of PBN's ability to scavenge f ree radicals, MDL 101,002 is currently being evaluated in stroke model s as a means to ameliorate the oxidative insult associated with reperf usion injury. To augment our understanding of the radical scavenging m echanism of this potential drug, MDL 101,002 was incubated with soybea n Lipoxygenase in the presence of linoleic acid to study the interacti on between MDL 101,002 and free radicals formed during lipid peroxidat ion. Analysis of the reaction mixture was performed by high performanc e liquid chromatography using normal phase conditions with detection b y atmospheric pressure chemical ionization mass spectrometry (APCI-MS) . Similar to the work by Iwahashi et al. [Arch. Biochem. Biophys., 199 1, 285, 172], who studied the spin trap alpha-(4-pyridyl-1-oxide)-N-te rt-butyl nitrone (4-POBN), an adduct that suggested the trapping of pe ntyl radicals by MDL 101,002 was observed. However, the apparent molec ular ion for this adduct (246 Da) was 1 Da lower than would be predict ed if a pentyl radical had simply added to MDL 101,002. In addition, t he adduct exhibited significant absorbance at 304 nm, consistent with the unsaturated nitrone structure of MDL 101,002. To account for these observations, it is postulated that, after the initial capture of a p entyl radical, subsequent abstraction of a hydrogen atom by a neighbor ing radical occurs to regenerate a nitrone (1-pentyl analog of MDL 101 ,002). We present evidence for this adduct and offer a mechanism for i ts formation. These findings indicate that mass spectroscopic analysis of stable nitrone radical adducts may be useful in the identification of radical-dependent damage in vivo and possibly in clinical developm ent of MDL 101,002 as an antioxidant pharmaceutical. Copyright (C) 199 7 Elsevier Science.