Aspartimide Formation

This very common side reaction occurs with aspartic acid or asparagine. The reaction occurs from formation of a five-membered imide. This intermediate can undergo a series of fates that result in various side products as shown below.

This side reaction occurs most frequently with peptides containing the Asp(OtBu)-X sequence, where X = Asn(Trt), Gly, Ser, Thr.