Base- and acid-catalyzed interconversions of O-acyl- and N-acyl-ethanolamines: a cautionary note for lipid analyses

The isolation and quantification of ethanolamine containing lipids from ani mal tissues may expose neutral lipid extracts to acidic or basic conditions during chromatographic separations or derivatization chemistry While inves tigating the acid- and base-catalyzed production of anandamide in chromatog raphic fractions of rat brain extracts not containing anandamide, we observ ed that O,N-acyl migrations are facile. O,N-acyl migrations are well docume nted in synthetic organic chemistry literature, but are not well described or recognized with regard to methods in lipid isolation or lipid enzyme stu dies. We report here the synthesis and characterization of O- and N-acyl (p almitoylor arachidonoyl-)ethanolamines. Their rearrangements in base and ac id are quantified by liquid chromatography-electrospray ionization mass spe ctrometry. The rearrangements proceed through a cyclic intermediate that is also formed during chemical reactions commonly used for derivatization of acylethanolamines for gas chromatography-mass spectrometry. The isolation a nd characterization of N- or O-acylethanolamines and their enzymatic format ion requires awareness and consideration of the proclivity of these compoun ds to chemically rearrange.