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New crystalline forms of hydrated and anhydrous N-acylhydrazones are reported. The studied crystal structures were determined by single-crystal X-ray diffraction at 90 or 100 K. Transferred aspherical atom model (TAAM) structure refinements were performed with the aid of the most recent version of the University at Buffalo Databank (UBDB). The resulting crystal structures were analyzed in terms of molecular conformations, intermolecular interaction energies, and crystal packing motifs. For this purpose, solid-state NMR studies and theoretical calculations were conducted supplementarily. It was found that all studied hydrazones adopt the E configuration around the azine N–N bond and imino NC function in the solid state, whereas the hydrazide N–N–CO moiety exhibits the E and Z arrangement in the N-acyl and N-aroyl derivatives, respectively. The constrained energy scans confirmed the E conformation of the hydrazide unit and the E arrangement of pyridine and hydrazone N atoms as the most stable ones. The association modes in the studied crystals are dominated by strong hydrogen bonds of the N–H···O or N–H···N-type involving the amide group as a proton donor. Consequently, as indicated by lattice energy calculations, a significant increase in the crystal cohesive energy per asymmetric unit is observed when water molecules are incorporated into the crystal structure, because this enables efficient saturation of the hydrogen bond acceptor and donor atoms. On the other hand, a substantial contribution of π···π stacking interactions to the overall stabilization of the crystal nets was also found. Thus, when more bulky phenyl substituents are introduced, the cohesive energy becomes more favorable.

This work presents the crystal structure determination of two elusive polymorphs of furazidin, an antibacterial agent, employing a combination of crystal structure prediction (CSP) calculations and an NMR crystallography approach. Two previously uncharacterized neat crystal forms, one of which has two symmetry-independent molecules (form I), whereas the other one is a Z 0 = 1 polymorph (form II), crystallize in P2 1 /c and P1 space groups, respectively, and both are built by different conformers, displaying different intermolecular interactions. It is demonstrated that the usage of either CSP or NMR crystallography alone is insufficient to successfully elucidate the abovementioned crystal structures, especially in the case of the Z 0 = 2 polymorph. In addition, cases of serendipitous agreement in terms of 1 H or 13 C NMR data obtained for the CSP-generated crystal structures different from the ones observed in the laboratory (false-positive matches) are analyzed and described. While for the majority of analyzed crystal structures the obtained agreement with the NMR experiment is indicative of some structural features in common with the experimental structure, the mentioned serendipity observed in exceptional cases points to the necessity of caution when using an NMR crystallography approach in crystal structure determination. research papers Acta Cryst. (2020). B76, 322-335 Marta K. Dudek et al. Two furazidin polymorphs 323 research papers Acta Cryst. (2020). B76, 322-335 Marta K. Dudek et al. Two furazidin polymorphs 331 Figure 10Hydrogen-bonding pattern in the experimental crystal structure of form I (a) and in the third-lowest-energy crystal structure (b), built by the same conformers as the experimental structure; hydrogen bonds are marked with dotted green lines.

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Flu is a serious health, medical, and economic problem, but no therapy is yet available that has satisfactory results and reduces the occurrence of these problems. Nearly 20 years after the registration of the previous therapy, baloxavir marboxil, a drug with a new mechanism of action, recently appeared on the market. This is a promising step in the fight against the influenza virus. This article presents the possibilities of using all available antiviral drugs specific for influenza A and B. We compare all currently recommended anti-influenza medications, considering their mechanisms of action, administration, indications, target groups, effectiveness, and safety profiles. We demonstrate that baloxavir marboxil presents a similar safety and efficacy profile to those of drugs already used in the treatment of influenza. Further research on combination therapy is highly recommended and may have promising results.

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