SYNTHESIS OF DEUTERIUM-LABELED PLANT STEROLS AND ANALYSIS OF THEIR SIDE-CHAIN MOBILITY BY SOLID-STATE DEUTERIUM NMR

The plant sterols sitosterol and stigmasterol exert very different eff ects on plant model membranes, the first one being a ''reinforcer'' li ke cholesterol, the second one not. 25-H-2-Stigmasterol has been synth esized by coupling of the 22-aldehyde derived from stigmasterol, by oz onolysis, with the proper sulfone labeled in position 25. The configur ation of the ethyl side chain at C-24 was controlled by separation of the diastereomers introduced via a chiral sulfoxide. This synthetic sc heme allowed the introduction of a labeled side chain in plant sterols in eight steps for stigmasterol and nine for sitosterol (overall yiel d ca. 15%). Using both diastereomers, the 24-epimers of sitosterol (cl ionasterol) and stigmasterol (poriferasterol) have also been synthesiz ed. Deuterium NMR on oriented lipid bilayers made of soybean phosphati dylcholine and containing these four labeled plant sterols clearly rev eals the difference of orientation and mobility of the four side chain s.