Salts, Cocrystals and Ionic Cocrystals of a “Simple” Tautomeric Compound

We have investigated the cocrystallisation behaviour of AHMP (2-amino-6-methyl-1,4-dihydropyrimidin-4-one) with a series of acids and imide coformers.
Being a base able to tautomerise, at the molecular level, AHMP may exist as three different neutral tautomers or, if protonated, in the form of several cationic species. Crystal engineering concepts were used in order to attempt selective isolation of several tautomers. For this, a series of acids and imides were used as coformers. Cocrystallisation with acids resulted in eleven new solid forms including salts, ionic cocrystals and cocrystals. Cocrystallisations with imides did not afford any new forms, while cocrystallisation with saccharin afforded two
polymorphic salts and an ionic cocrystal. Two of the possible tautomers were obtained as well as one of the cationic species. DFT calculations were carried out in order to rationalize the molecular species obtained as well as the supramolecular motifs. Despite being a small “simple” molecule, AHMP has a very rich and interesting solid form landscape with cocrystals containing two different tautomers, many salts (some of which are polymorphic) and multiple ionic cocrystals.