(485c) Development of Solid Phase Peptide Synthesis Kinetic Models for Impurity Control Strategies

Therapeutic peptides have gained significant attention as promising new modality for treating patients’ unmet medical needs and as of 2022 there are now 100 peptide drugs approved in the US. Solid phase peptide synthesis technology is the most common methodology used to manufacture these valuable medicines due in part to the facile ability to incorporate non-coded amino acids. Peptides are inherently complex molecules with potentially multiple impurities such as single amino acid deletion, racemization and addition impurities which need to be controlled at low levels to meet critical quality attributes.

Solid phase peptide synthesis generally involves three chemistry cycles including deprotection, activation and coupling. Deprotection reactions generally use base to remove the amine protecting group. Activated esters are synthesized from amino acids, then the activated ester couples with the amine group of the on-resin peptide to form an amide bond. Additionally, a capping step may be applied to unreacted amines in order to minimize propagation of deletion impurities. The cycle is repeated until the desired peptide sequence is obtained. The entire process often involves dozens of unit operation cycles with potentially hundreds of process parameters to control.

A conventional experimental design strategy for complex peptides can be time consuming amid numerous variables involved. For this reason, this work introduces a detailed mechanistic solid phase peptide synthesis model to correlate the relationship between input parameters and response impurity profile. The model formula is proposed, applying elementary mechanistic reaction steps and kinetics parameters that were fitted based on data obtained from literature. ^{1, 2} Sensitivity analysis is applied to understand impact of process parameter ranges to impurity levels and corresponding control strategies are recommended.

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2. McFarland, A. D.; Buser, J. Y.; Embry, M. C.; Held, C. B.; Kolis, S. P., Generation of Hydrogen Cyanide from the Reaction of Oxyma (Ethyl cyano (hydroxyimino) acetate) and DIC (Diisopropylcarbodiimide). Org. Process Res. Dev. 2019, 23 (9), 2099-2105.