During the synthesis of large protein targets, it becomes advantageous to conduct steps in a 'one-pot' fashion, minimizing lengthy and yield-reducing purification maneuvers. For example, directly after a NCL reaction, the desulfurization step can be performed in one pot, followed by Cys(Acm) deblocking without intermediate purification. A primary limitation of performing desulfurization immediately after NCL, is that a large excess of thiol catalyst, usually 4-mercaptophenylacetic acid (MPAA) is needed to improve ligation rates but they also quench the desulfurization reaction. Efforts have been directed toward finding new thiol catalysts that are compatible with desulfurization (Table , Entries 16-18). Methyl thioglycolate was found to not interfere with desulfurization whilst providing good catalytic properties, and it has been used in the synthesis of mirror-image ubiquitin for racemic protein crystallography studies. Other efforts to reduce the number of HPLC purification steps include one-pot ligations of numerous fragments and performing chemical ligations on a solid support.