Figure 3 – Crude peptide chromatogram with impurities > 0.3 % highlighted & characterised
‣ Process development & impurity control
The classic model for peptide manufacture involves three stages : solid-phase synthesis , cleavage / deprotection and purification / ionexchange . Figure 2 shows the types of impurities generated in each stage and the potential controls that can be investigated during process development . Just as the specification of a peptide is dependent on finalisation of the analytical method , clearly so is process development . Chemists performing process development must test development samples using the finalised analytical method . Ideally , the final method should be compatible to allow direct analysis of crude peptide and preparative HPLC fractions in a suitable timeframe , so that individual impurities can be tracked and an assessment can be performed of impurities that are difficult to control through purification alone . This leads to a better understanding of which impurities must be controlled at source . Figure 3 shows an example . Classifying the source of impurities for the process development team to focus on the impurities that are
difficult to control during purification and hence must be controlled upstream . Impurities identified as degradants are those that form during the downstream process , for example deamidation . Control through careful pH and temperature in the process is typically employed . Bespoke solutions are usually required to control specific impurities formed during synthesis . Such solutions may be through the judicious choice of coupling / deprotection conditions , the inclusion of a dipeptide or choice of scavengers used in the cleavage / deprotection step . In other examples , control of an isomeric impurity is possible by changing the conditions used for coupling of a specific amino acid . In other cases , impurities that have formed under cleavage conditions have been controlled simply by the addition of an alternative scavenger .
Conclusions
The use of peptides as therapeutics is now an embedded technology in the pharmaceutical industry , with the majority being manufactured using fully synthetic processes . The chemistry used to make peptides is well established and has resulted in regulatory bodies viewing peptides as quite different from biologics , with an increased expectation of control of the process and impurity profiles . This , coupled with increased scrutiny of peptides through advances in analytical technologies , has led to the requirement for process development teams to understand how individual impurities are formed and how these may be controlled in the manufacture at an earlier stage of clinical development . As analytical development continues , separation of previously co-eluting impurities can change the specification requirements for a peptide , which means the process development team must have a range of tools available to ensure control of impurities throughout the manufacturing process . •
Angeliki Galoozis
SENIOR PUBLIC RELATIONS ASSOCIATE
References 1 : www . fda . gov / files / drugs / published / ANDAs-for-Certain-Highly-Purified-Synthetic-Peptide-Drug-Products-That-Refer-to-Listed-Drugs-of-rDNA-Origin-Guidance-for-Industry . pdf 2 : EP General Monograph 2034 : ‘ Substances for Pharmaceutical Use ’, Table 2034.2
54 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981