The synthesis and molecular dynamics of phospholipids having hydroxylated fatty acids at the sn-2 position.

We have devised a general method for the synthesis of phospholipids containing hydroxylated fatty acids and have utilized this methodology to synthesize two naturally occurring hydroxylated lecithins (i.e. 1-palmitoyl-2-[15(S)-hydroxy-5E, 8E,11E,13Z-eicosatetraenoyl]-sn-glycero-3-phosph ocholine (1-palm-2-15HETE PC) and 1-palmitoyl-2-[5-hydroxy-6Z,8E,11E, 14E-eicosatetraenoyl]-sn-glycero-3-phosphocholine (1-palm-2-5HETE PC]. After protection of the hydroxylated fatty acid as its t-butyldimethylsilyl derivative, the anhydride of the protected fatty acid was formed utilizing dicyclohexylcarbodiimide and subsequently was condensed with a regiospecific lysolecithin utilizing pyrrolidinopyridine as catalyst to form the protected hydroxylated lecithin. Finally, hydroxylated lecithins were formed after removal of the t-butyldimethylsilyl group with acetic acid. Electron spin resonance spectroscopy was utilized to interrogate the molecular dynamics of lipid bilayers comprised of mixtures of these hydroxylated lecithins and naturally occurring lecithins. Remarkably, the molecular dynamics of spin-labeled phospholipids in liposomes comprised of cholesterol and phosphatidylcholine were altered substantially after addition of only 3.5 mol% 1-palm-2-15HETE PC as assessed by the order parameter of 16-doxylstearoyl phosphatidylcholine.