(513b) Model-Aided Reaction Kinetics and Rheology Study of Solid Phase Peptide Cleavage Process

Solid phase peptide synthesis is a widely used technique for the synthesis of medicinal peptides. In such processes, the desirable peptide sequence is built on a polystyrene resin bead via cyclic reaction sequence, i.e., activation of Fmoc- protected amino acid to form activated ester, coupling of activated ester on the amine group of the peptide that attached to the resin, and then deprotection of Fmoc- protection group to expose the amine group ready for next amino acid coupling. Once synthesis is completed and the designed peptide sequence is obtained, a subsequent peptide isolation technique is frequently used where trifluoroacetic acid/dichloromethane solution mixture is applied to allow the cleavage of peptide from the resin. The peptide is then isolated via distillation, precipitation/crystallization, and drying unit operation processes. However, the peptide is subject to degradation in the acidic cleavage solution. Also, there can be significant peptide gelation issues during the cleavage reaction, where formed peptide networks dynamically increase the solution viscosity and pose significant operation risk in manufacturing. In this study, a systematic model-aided peptide kinetics and rheology study is applied to quickly identify the optimal reaction conditions using the minimum number of experiments. The reaction kinetics study was conducted with the aid of a mid-FTIR probe to track peptide and TFA solution concentrations during reaction in real-time. A detailed peptide cleavage/impurity formation kinetics model is proposed and the adsorption isotherm of TFA is considered to allow precise identification of optimal reaction conditions. Then a dynamic rheology study was applied to monitor the peptide gelation network kinetics during the soft-cleavage reaction to demonstrate acceptable solution viscosity during production process time. Combing the reaction kinetics/impurity control and gelation phase diagram, this novel approach has the potential to apply for quick rational design of any solid phase peptide isolation process.