Chemical synthesis and 2H NMR investigations of polyisoprenols: dynamics in model membranes.

Polyisoprenols (PIs) such as dolichol and undecaprenol have been shown to play an important role as enzymatic cofactors in the synthesis of glycoconjugates of both prokaryotic and eukaryotic cells. Presented here is a synthetic route used for obtaining specifically labeled [omega,omega-(C2H3)2]PIs that initiates with the selective oxidation of the omega-terminal double bond of the PI with N-bromosuccinimide. Continuation of the reaction sequence produces an omega-terminal aldehyde three carbons shorter than the original PI. A Wittig reaction with an appropriate deuterium-labeled phosphonium salt is then used to form an omega-terminal-deuterated PI identical with the starting material except for replacement of 1H with 2H at the two omega-terminal methyls of the PI. Deuterium NMR spectra of [omega, omega-(C2H3)2]geraniol and -farnesol incorporated into phospholipid multilamellar vesicles show powder patterns. The quadrupole splitting of the 2H NMR signals was interpretable in terms of the degree of orderedness of the 2H-labeled site. The pure trans isomer geraniol gave rise to a single set of splittings for each C2H3 group while farnesol, a mixture of isomers, showed multiple quadrupole splittings. The quadrupole splittings of the PIs increased with increasing concentration of label and with lowering of temperature. Deuterium NMR T1 measurements, revealing rates of motion of the 2H-labeled site, showed fast motion for [omega,omega-(C2H3)3]geraniol relative to [omega,omega-(C2H3)2]cholesterol under similar conditions. A correlation time of 5 X 10(-10) s was estimated for [omega,omega-(C2H3)2]geraniol, which was 1 order of magnitude faster than for [26,27-(C2H3)2]cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)