Choline phospholipids (diether and dialkyl analogs of phosphatidyl choline, cholesteryl phosphocholine) were prepared, in yields of 72–83%, by condensation of the diglyceride analogs (or cholesterol) with phosphorusoxychloride and choline toluene‐sulfonate.

NotesFrom a synthetic point of view methanolysis of 1 (and likely similar unimolecular solvolyses) appears to be of limited usefulness. Solvolysis of 1 and 2 in aprotic solvents in the presence of strong nucleophiles should conversely represent a good alternative to the displacement of analogous 21-chloro derivatives lg2 and 2c5 for the introduction of substituents at C-21. Experimental Section617a-Pregna-5,20-dien-3/S,17-diol 3-Acetate 17-Trifluoroacetate (1). A solution of 17a-pregna-5,20-dien-3/3,17-diol 3-acetate (la)2 (0.36 g, 1 mmol) in pyridine (1.7 mL) was treated with trifluoroacetic anhydride (0.7 mL) at 0 °C for 15 min. Then cold 1 N HC1 (11.7 mL) was added and the mixture was extracted with ether. The ether layers were washed to neutrality with cold water, dried (Na2S04), and evaporated. The residue (0.45 g) was crystallized from n-hexane (0.33

The permeability of an N-oleoyldihydrosphingomyelin bilayer against glycerol was similar to that of a bilayer of phosphatidylcholine with identical effective hydrophobic chain length. Cholesterol at 1:1 molar ratio reduced the permeability, and also reduced the energy of activation of glycerol penetration, an effect not found for diesterphosphatidylcholine with cholesterol. The higher level of the ground state of the entropy of activation for permeability can be interpreted in terms of a hydrogen belt model which postulates lipid-lipid hydrogen bonding in membranes and explains the effect found as a disturbance of the hydrogen belt structure. Dihydrosphingomyelin can be considered to function as an "extender" in the hydrogen belt network.

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