Editing Synthesis of Lipids (section)

=== Method 2  ===

1. N-[1 -(2,3 -diacyloxy ) propyl ] -N,N,N-trimethyl-ammonium methyl sulfate ( DAcylTAP ) ( general&nbsp;description )&nbsp;Oleic-, stearic-, palmitic-, myristic-, or lauric<br>acid (15.8 mmol), was dissolved in 25 ml of THF.&nbsp;N,N’-carbonyldiimidazole (CDI), 2.82 g (17.4 mmol), was added and the&nbsp;mixture was stirred for 30 min at rt. 3-Dimethyl-amino-1,2-propanediol, 750 mg (6.30 mmol) and&nbsp;n-BuLi (15% in hexane) 200 ml (0.315 mmol) were&nbsp;added and the reaction was refluxed for two days.&nbsp;The solvent was removed using a rotatory&nbsp;evaporator. 100 ml of acetone and dimethyl sulfate, 2.0 ml (21.1 mmol) were added and the&nbsp;solution was stirred for further two days&nbsp;at 4°C. The precipitated product was isolated by&nbsp;filtration and recrystallized from acetone. Yield:&nbsp;30 – 40%. 

In analogy with the procedures described by&nbsp;Leventis and Silvius for the synthesis of DOTAP&nbsp;(Leventis and Silvius, 1990) with iodide as counter&nbsp;ion and of its ether analog DOTMA (Felgner et&nbsp;al., 1987), the synthesis is based on the commercially available 3-dimethyl-1,2-propanediol (1). In&nbsp;contrast to the method published by Leventis,&nbsp;who acylated 1 using oleic acid chlorides in&nbsp;pyridine, our reaction sequence applies fatty acid&nbsp;imidazolides as acylating agents. They are prepared in situ from the respective fatty acids and&nbsp;N,N’-carbonyldiimidazole (CDI) (Staab and&nbsp;Mannschreck, 1962). As both the imidazolide formation and the following acylation of 1 (in refluxing THF with a catalytic amount of n-BuLi)&nbsp;occur without formation of insoluble by-products<br>like pyridine hydrochlorides, neither extraction&nbsp;nor filtration is necessary.&nbsp;The products, the 1,2-diacyl-3-dimethylamino-propanes (2a–e) need not to be isolated, only the&nbsp;solvent has to be replaced by acetone. For subsequent methylation, dimethyl sulfate is added. Due&nbsp;to the solvent characteristics of acetone, the&nbsp;methylated (quaternized) products (3a–e) precipition step from acetone is sufficient. The overall&nbsp;yields range from 30 to 40%, which is only slightly&nbsp;lower than described for the much more complicated original DOTAP-synthesis (49% for&nbsp;DOTAP). 

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[[Image:DOTAP Synthesis.png]] 

Synthesis of DL 1,2-dipalmitoyl-3-propyltrimethylammonium chloride (DPTMA diester).<br>This compound was synthesized by using palmitoyl chloride instead of oleoyl chloride in the above procedure.