New multi-component solid forms of anti-cancer drug Erlotinib: role of auxiliary interactions in determining a preferred conformation

Erlotinib is a BCS (biopharmaceutical classification system) class II drug used for the treatment of non‐small cell lung cancer. There is an urgent need to obtain new solid forms of higher solubility to improve the bioavailability of the API (active pharmaceutical ingredient). In this context, cocrystals with urea, succinic acid, and glutaric acid and salts with maleic acid, adipic acid, and saccharin were prepared via wet granulation and solution crystallizations. Crystal structures of the free base (Z′ = 2), cocrystals of erlotinib–urea (1:1), erlotinib–succinic acid monohydrate (1:1:1), erlotinib–glutaric acid monohydrate (1:1:1) and salts of erlotinib–adipic acid adipate (1:0.5:0.5) are determined and their hydrogen‐bonding patterns are analyzed. Self recognition via the (amine) N—H…N (pyridine) hydrogen bond between the API molecules is replaced by several heterosynthons such as acid–pyridine, amide–pyridine and carboxylate–pyridinium in the new binary systems. Auxiliary interactions play an important role in determining the conformation of the API in the crystal. FT–IR spectroscopy is used to distinguish between the salts and cocrystals in the new multi‐component systems. The new solid forms are characterized by powder X‐ray diffraction (PXRD) and differential scanning calorimetry (DSC) to confirm their unique phase identity. Erlotinib, an anti‐cancer drug, was screened for the preparation of new multi‐component systems. The drug exists in two conformations. The syn conformation is observed in the cocrystals and salts with weaker acids, while the anti conformation is observed in the HCl salt. Details of the structural aspects of the new solid forms are presented.