Kinetic Studies of the Liquid Phase Peptide Synthesis

Kinetic studies were carried out on the newly developed “liquid-phase” method (LPM) for peptide synthesis, using soluble polymer esters of amino acids. The reaction rates of these polymer-bound amino acids (esters of polyethylene glycol with molecular weights in the range of 2,000 to 20,000) were compared with those of the low molecular weight components used in classical peptide coupling reactions. New techniques for evaluating spectroscopic data have enabled the peptide coupling reaction to be studied precisely. The reactions were shown to be of the second-order type. The comparison indicated that the LPM system showed analogous kinetic behavior to the system used for classic peptide synthesis. The reaction rates are of the same order of magnitude and both systems revealed linear kinetic behavior. Under otherwise identical conditions the presence of the polyethylene glycol esters caused an increase in reaction rate compared with the corresponding low molecular weight analogs. This was interpreted as being due to tautomeric catalysis.