Improving 2-Chlorotrityl Chloride (2-CTC) Resin Activation

Used in solid-phase peptide synthesis (SPPS) for peptides with an acid termination, the 2-chlorotrityl chloride (2-CTC) resin is highly susceptible to moisture, leading to reduced resin loading and lower synthetic yields. It is therefore recommended that the resin be activated with thionyl chloride (SOCl₂) before peptide assembly. Here we present an optimized procedure for resin activation that minimizes the use of SOCl₂ as the activation reagent and reduces the activation time. Additionally, we demonstrate the feasibility of reusing the 2-CTC resin when following the activation protocol, achieving comparable results to the first usage of the resin. Moreover, we achieved different degrees of resin activation by varying the amount of SOCl₂. For instance, the use of 2% SOCl₂ in anhydrous dichloromethane (DCM) allowed up to 44% activation of the resin, thereby making it suitable for the synthesis of longer peptides. Alternatively, employing 25% SOCl₂ in anhydrous DCM resulted in up to 80% activation with a reaction time of only 5 min in both cases.