Long chain arginine esters: A new class of cationic detergents for preparation of hydrophobic ion-paired complexes

The ability of stoichiometric amounts (based on charged groups) of ionic detergents to bind to oppositely charged ionic compounds has been recently reviewed. These hydrophobic ion-paired (HIP) complexes display altered solubility properties. Most of the work to date on HIP compelxes has focused on basic drugs and anionic detergents. It would be extremely useful to extend this approach to acidic compounds, including DNA and RNA. However, most cationic detergents are relatively toxic. It is hypothesized that detergents constructed from naturally occurring or well tolerated components, coupled by labile linkages, will be less toxic and still able to form strong HIP complexes. This study describes the synthesis and characterization of long chain alkyl esters of arginine. This class of cationic detergents, which have not been reported previously, are less cytotoxic than alkyltrimethylammonium detergents, possibly making them more acceptable in drug delivery applications. These arginine esters exhibit detergent-like properties. For example, the dodecyl ester of arginine has a critical micelle concentration of 0.07 mM, while being approximately 5-10 fold less toxic than tetradecyltrimethylammonium bromide. The arginine dodecyl ester forms stable HIP complexes with plasmid DNA. The complex is sufficiently stable to allow some modest level of transfection with Cos-7 cells in a time- and concentration-dependent fashion. This work demonstrates that arginine-based cationic detergents are effective ion-pairing agents, appear to be less toxic than alkyltrimethylammonium compounds, and form stable complexes with DNA.