| Abstract: | Abstract: During the manufacture of a proprietary peptide drug substance a new impurity appeared unexpectedly. Investigation of its chemical structure established the impurity as a β‐Ala insertion mutant of the mother peptide. The source of the β‐Ala was identified as contamination of the Fmoc‐Ala‐OH raw material with Fmoc‐β‐Ala‐Ala‐OH. Further studies also demonstrated the presence of β‐Ala in other Fmoc‐amino acids, particularly in Fmoc‐Arg(Pbf)‐OH. In this case, it was due to the presence of both Fmoc‐β‐Ala‐OH and Fmoc‐β‐Ala‐Arg(Pbf)‐OH. It is concluded that β‐Ala contamination of Fmoc‐amino acid derivatives is a general and hitherto unrecognized problem to suppliers of Fmoc‐amino acid derivatives. The β‐Ala is often present as Fmoc‐β‐Ala‐OH and/or as a dipeptide, Fmoc‐β‐Ala‐amino acid‐OH. In collaboration with the suppliers, new specifications were introduced, recognizing the presence of β‐Ala‐related impurities in the raw materials and limiting them to acceptable levels. The implementation of these measures has essentially eliminated β‐Ala contamination as a problem in the manufacture of the drug substance. |
