Synthesis of cholesteryl polyamine carbamates: pK(a) studies and condensation of calf thymus DNA

Novel polyamine carbamates have been designed and prepared from cholesterol . Our synthesis uses an orthogonal protection strategy based upon trifluoro acetyl and Boc-protecting groups. These unsymmetrical polyamine carbamates have been prepared from symmetrical (e.g., spermine and thermine) polyamine s. Detailed interpretations of H-1 and C-13 NMR spectroscopic data led to t he unambiguous assignment of these polyamine carbamates. These target conju gates contain a variety of positive charges distributed along methylene cha ins. Their pK(a)s have been determined potentiometrically for conjugates su bstituted with up to five amino functional groups. Condensation of calf thy mus DNA into particles was monitored using light scattering at 320 nm. Salt -dependent binding affinity for calf thymus DNA was determined using an eth idium bromide fluorescence quenching assay. These cholesteryl polyamine car bamates are models for lipoplex formation with respect to gene delivery (li pofection), a key first step in gene therapy.