4-Ureidophthalimide or ureido isoindolin-1-one based ligands were shown by NMR spectroscopy and theoretical studies to bind the CG base pairs in the major groove. To examine this hydrogen-bonded complex, we cocrystallized 5-fluorocytosine, 9-methylguanine and 1-(2-methyl-3-oxoisoindolin-5-yl)urea. Two polymorphs of the latter compound were obtained during the cocrystallization attempts. Both crystallized in monoclinic space groups: form Ia in P21/c with cell parameters of a = 11.382(2), b = 6.042(1), c = 14.102(2) Å and β = 96.51(1)°, and form Ib in P21/n with cell parameters of a = 7.092(1), b = 11.643(2), c = 11.580(2) Å and β = 93.48(1)°. An identical molecular conformation of the two polymorphs is observed. Both polymorphs have an R 2 2 (8) N–H···O interaction linking the urea fragments of two molecules to a centrosymmetric dimer. Nevertheless, the crystal packing for both forms is completely different. In Ia, two dimers are connected by two R 2 1 (6) N–H···O bonds simultaneously to a shifted ribbon motif, whereas in Ib the two R 2 1 (6) interactions link two molecules from two different dimers.
Graphical Abstract
Two polymorphs of 1-(2-methyl-3-oxoisoindolin-5-yl)urea show similar R 2 2 (8) and R 2 1 (6) hydrogen-bond patterns but one completely different crystal packing.