Chlorotrityl Chloride (CTC) Resin as a Reusable Carboxyl Protecting Group

Chlorotrityl Chloride (CTC) resin is one of the most useful resins for the solid‐phase synthesis of C‐terminal acid peptides. CTC resin can be used for the preparation of both protected and unprotected peptides. Herein, the use of CTC resin as a reusable mild protecting group of carboxylic acids is introduced. Temporary protection of carboxylic acids in solution is not a straightforward process, but the use of CTC resin is shown to be an alternative to classic solution procedures. Regeneration of the CTC resin after cleavage of the target compounds is feasible, which allows the reuse of the resin. Applications described herein encompass the preparation of noncommercial amino acids as well as complex dipeptides.