O‐ethylphosphatidylcholine: A metabolizable cationic phospholipid which is a serum‐compatible DNA transfection agent

1,2‐Dioleoyl‐sn‐glycero‐3‐ethylphosphocholine was prepared in a one‐step reaction from phosphatidylcholine by reaction with ethyl trifluoromethanesulfonate. This and related O‐alkyl phosphati‐dylcholines constitute the first chemically stable triesters of biological lipid structures and the first cationic derivatives of phospholipids consisting entirely of biological metabolites linked with ester bonds. The complex of cationic phospholipid and plasmid DNA transfected cells with high efficiency. Maximum efficiency of transfection was obtained with complexes in which the positive charge was a few percent in excess over the negative charge. Modest stimulation of transfection of common cell lines was obtained by continuous culture in the presence of 10% serum. Incubation of the phospholipid complex for at least 2 h at 37 °C in nearly pure serum had no deleterious effects on transfection efficiency. The lipid has low toxicity; BHK cells tolerated amounts of 2 mg/2 × 106 cells at concentrations of 1 mg/mL. The lipid is biodegradable; it was hydrolyzed by phospholipase A2 in vitro and was metabolized with a half‐life of a few days in cells in culture. The synthetic route to cationic phospholipids is well suited to the preparation of derivatives that are tailor‐made to have a wide variety of different properties.