Stereospecific inhibition of CETP by chiral N,N-disubstituted trifluoro-3-amino-2-propanols

Chiral N,N-disubstituted trifluoro-3-amino-2-propanols represent a recently discovered class of compounds that inhibit the neutral lipid transfer acti vity of cholesteryl ester transfer protein (CETP). These compounds all cont ain a single chiral center that is essential for inhibitory activity. (R,S) SC-744, which is composed of a mixture of the two enantiomers, inhibits CET P-mediated transfer of [H-3]cholesteryl ester ([H-3]CE) from HDL donor part icles to LDL acceptor particles with an IC50 = 200 nM when assayed using a reconstituted system in buffer and with an IC50 = 6 muM when assayed in pla sma. Upon isolation of the enantiomers, it was found that the (R,+) enantio mer, SC-795, was about 10-fold more patent than the mixture, and that the ( S,-) enantiomer, SC-794, did not have significant inhibitory activity (IC50 > 0.8 muM). All of the activity of the (S,-)SC-794 enantiomer could be acc ounted for by contamination of this sample with a residual 2% of the highly potent (R,+) enantiomer, SC-795. The IC50 of (R,+)SC-795, 20 nM, approache d the concentration of CETP (8 nM) in the buffer assay. These chiral N,N-di substituted trifluoro-3-amino-2-propanols were found to associate with both LDL and HDL, but did not disrupt overall lipoprotein structure. They did n ot affect the on or off rates of CETP binding to HDL disk particles. Inhibi tion was highly specific since the activities of phospholipid transfer prot ein and lecithin cholesterol acyl transferase were not affected. Competitio n experiments showed that the more potent enantiomer (R)SC-795 prevented ch olesteryl ester binding to CETP, and direct binding experiments demonstrate d that this inhibitor bound to CETP with high affinity and specificity. It is estimated, based on the relative concentrations of inhibitor and lipid i n the transfer assay, that (R)SC-795 binds approximately 5000-fold more eff iciently to CETP than the natural ligand, cholesteryl ester. We conclude th at these chiral N,N-disubstituted trifluoro-3-amino-2-propanol compounds do not affect lipoprotein structure or CETP-lipoprotein recognition, but inhi bit lipid transfer by binding to CETP reversibly and stereospecifically at a site that competes with neutral lipid binding.