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 animal tissues may expose neutral lipid extracts to acidic or basic conditions during chromatographic separations or derivatization chemistry. While investigating the acid- and base-catalyzed production of anandamide in chromatographic fractions of rat brain extracts not containing anandamide, we observed that O,N-acyl migrations are facile. O,N-acyl migrations are well documented in synthetic organic chemistry literature, but are not well described or recognized with regard to methods in lipid isolation or lipid enzyme studies. We report here the synthesis and characterization of O- and N-acyl (palmitoyl- or arachidonoyl-)ethanolamines. Their rearrangements in base and acid are quantified by liquid chromatography;-electrospray ionization mass spectrometry. 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 and characterization of N- or O-acylethanolamines and their enzymatic formation requires awareness and consideration of the proclivity of these compounds to chemically rearrange.