4-Methyl erlotinib

4-Methyl erlotinib is a quinazoline-based API impurity characterized by a methyl substitution at the 4-position of the quinazoline core, distinguishing it from the parent drug erlotinib. The molecule retains the pyridine-linked anilinoquinazoline scaffold but features a methoxyphenyl ester moiety and a methyl group at the 4-position, altering its electronic and steric properties. This structural modification reduces its kinase-inhibitory activity compared to erlotinib. It arises as a synthetic byproduct during erlotinib production via alkylation at the quinazoline ring. This compound serves as a critical HPLC reference standard for quantifying process-related impurities in erlotinib formulations.