Reducing agents used for end-cap removal of immunoglobulins or their antigen-binding fragments.

Abstract

A compound formed by combining multiple water-soluble functional groups with triarylphosphine compounds represented by the following chemical formulas as a reducing agent for an active ingredient can be used as a reducing agent to selectively remove the end cap of cysteine ​​residues (amino acid number 80 according to Kabat) in the variable region of the light chain of immunoglobulins or their antigen-binding fragments (R1, R2 and R3 are each independently aryl or heteroaryl).