Sulfamethazine is known to cocrystallize with carboxylic acids yielding over a dozen sulfamethazine-carboxylic acid cocrystals in the Cambridge Structural Database. Sulfisomidine, however, which differs from sulfamethazine only in the position of the second pyrimidine nitrogen, does not easily cocrystallize with carboxylic acids and to date has yielded no acid cocrystals in the CSD. Recently we have been able to grow 11 sulfisomidine cocrystals with mono-substituted benzoic acids and have solved the crystal structures of several of these. As expected, the carboxylic acid hydrogen bonds to the aminopyrimidine through an R<sup>2</sup><sub>2</sub>(8) dimer shown in the figure below where when A = CH and B = N the drug is sulfamethazine and when A = N and B = CH the drug is sulfisomidine. While the amidine tautomer shown below is seen in all of the sulfamethazine cocrystals, the sulfisomidine cocrystals display a mixture of amidine and imidine tautomers in their cocrystals. Our work focuses on the analysis of sulfamethazine and sulfisomidine cocrystal structures emphasizing the similarities and differences observed in the hydrogen bond pattern, sulfonamide conformation, and observed tautomer. This poster will present the results of these analyses.

Crystal structure comparision of sulfisomidine and sulfamethazine cocrystals with various benzoic acids

251st National Meeting (2016)

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