Identification and removal of a cryptic impurity in pomalidomide-PEG based PROTAC

Area of Science:

• Medicinal Chemistry
• Organic Synthesis
• Biochemistry

Background:

• Chemically induced dimerization is crucial for studying protein function.
• PROTACs, often using IMiD-based molecules and PEG linkers, are key tools for targeted protein degradation.
• Standard synthesis involves nucleophilic aromatic substitution of 4-fluorothalidomide.

Purpose of the Study:

• To identify impurities in the synthesis of IMiD-based PROTACs.
• To investigate competing reaction pathways during synthesis.
• To develop methods for impurity mitigation.

Main Methods:

• Analysis of synthesis byproducts using High-Performance Liquid Chromatography (HPLC).
• Investigation of nucleophilic aromatic substitution vs. nucleophilic acyl substitution.
• Application of taurine scavenging for impurity removal.

Main Results:

• A significant impurity, arising from nucleophilic acyl substitution, was identified.
• This impurity can co-elute with the desired PROTAC product on HPLC.
• Taurine scavenging effectively minimizes the identified glutarimide-displacing byproduct.

Conclusions:

• The standard synthesis of IMiD-based PROTACs can generate a problematic impurity.
• Understanding competing reaction mechanisms is vital for optimizing synthesis.
• Taurine scavenging offers a practical solution to enhance product purity.