Synthesis of spin-labelled 2-(16'-(N-oxyl-4'',4''-dimethyloxazolidine)stearoyl)-phosphatidylcholine.

Chemical synthesis of spin-labelled lecithin 2-(16'-(N-oxyl-4'',4''-dimethyloxazolidine)stearoyl)-phosphatidylcholine was achieved by reaction of equimolar amounts of purified egg yolk lyso-lecithin with commercially available 16-(N-oxyl-4',4'-dimethyloxazolidine)stearic acid activated with N,N-carbonyldiimidazole. After purification by silicic acid column chromatography, spin-labelled lecithin was obtained in 52.2% yield and had an ester: phosphorus:spin molar ratio of 2.0:1.1:1.0. When dimyristoyl-phosphatidylcholine and dimyristoyl-phosphatidylcholine:cholesterol (10:1) liposomes, containing 2-(16'-(N-oxyl-4'',4''-dimethyloxazolidine)stearoyl)-phosphatidylcholine as a probe were examined for thermotropic changes monitored by electron spin resonance spectroscopy, transition temperatures of 24.0 and 24.2 degrees C, respectively, were obtained in a very good agreement with previously reported values obtained with different probes and by different techniques, and with our own differential scanning calorimetry measurements. The potential usefulness of synthetic 2-(16'-(N-oxyl-4'',4''-dimethyloxazolidine)stearoyl)-phosphatidylcholine as a spin-label probe in studies of lipid-protein interactions in biological membranes was discussed.