Synthesis and physical chemical properties of CF3O-containg secondary amines—Perspective building blocks for drug discovery

Conformational and electronic effects of the trifluoromethoxy group make it attractive to be introduced in biorelevant structures. A mini-library of CF3O-substituted piperidines, pyrrolidines and azetidines was synthesized in 4-5 steps from commercial amino alcohols. Comparison of the measured pKa- and log D7.4 values of selected regioisomeric CF3O piperidines with the corresponding CF3- and MeO analogues shows that the effect on the acid/base properties and lipophilicity is rather complex and depends of the substitution position and the conformation of the molecules. For the most stable conformers of β-OCF3 compounds 2-(trifluoromethoxymethyl)piperidine (1c) and 3-trifloromethoxypiperidine (1e), DFT calculations and X-ray data (for 1c) show a favored gauche-arrangement with regard to the amino group.