Fluorine-, pyrene-, and nitroxide-labeled sphingomyelin: semi-synthesis and thermotropic properties

A rapid, high-yield method has been developed for the N-acylation of sphingosine-1-phosphocholine (SPC) to obtain a series of sphingomyelin (SM) derivatives bearing different reporter groups in the N-acyl chain. The procedure utilizes a fatty acid activated as the N-hydroxysuccinimide ester. A 1:1 molar mixture of the activated fatty acid and SPC is refluxed in 5% aqueous NaHCO3-ethanol 9:1 (v/v) for 2-3 hr. After acidification, the precipitated SM is purified by column chromatography over silica gel. This procedure offers significant advantages over those reported for the synthesis of well-defined SM: i) only the amino (not the hydroxyl) group is acylated; ii) only one equivalent of fatty acid is required; and iii) the time necessary for the reaction to go to completion is short. The transition temperature and enthalpy of each SM derivative has been measured by differential scanning calorimetry and compared to its unlabeled analog.