In addition to these four structures identified in earlier experimental and computational studies, our calculations also predicted a low-energy candidate structure in the P21/c space group (Rank 4 prediction). Both the putative form III* in the Pbca space group and the newly identified P21/c structure have identical 2D layers as the experimental form II, but the packing along the third dimension differs, similar to Aspirin's crystalline forms I and II. The simulated PXRD data of this P21/c structure matched better with the characteristic peaks assigned to experimental form III (Figure in SI). These results challenge the conclusion from Ref. that the experimentally observed form III corresponds to the Pbca structure, as it appears that our predicted P21/c candidate structure can better explain the experimental data. Furthermore, since the lattice parameters of the P21/c structure are very close to those of form II, it is more likely than form III* to grow together with form II. It is also possible that the experimentally observed form III might be a mixture of the predicted P21/c and Pbca candidate structures. GSK269984B GSK268499B, a drug candidate developed by GlaxoSmithKline, has been reported as an EP(1) receptor antagonist for the treatment of inflammatory pain. Previous studies combining experimental screening and CSP have concluded that form I is the most stable anhydrous crystal structure. Interestingly, form I does not possess strong intermolecular hydrogen bonding apart from intermolecular halogen bonds and pi-pi interactions, as shown in Figure (m). Instead, it contains intramolecular hydrogen bonds between the carboxylic acid proton and pyridine nitrogen.