ИСТИНА

Recently, we have introduced a concept of “stereochemical chameleon”, i.e., a functional group, which could exhibit ether donor or acceptor behavior depending on its surrounding and conformation1. One of the most exciting examples of such groups is the amide group widespread in nature and extremely important synthetically. The typical and acknowledged property of amide moiety is its planarity, which is a result of N-CO conjugation; in some cases, this planarity causes the existence of stereisomeric E- and Z-forms. Under some conditions, the amide group could undergo inversion of its configuration, which could be stable under other conditions. When we have two amide functionalities in one molecule, they could influence each other, provided they are spatially aligned in a close proximity. Bispidine scaffold seems to be highly useful platform in this respect since N,N’-bis-amides could exist in either anti- or syn-isomers. In the frames of our studies on bispidine-type ligands for 64Cu-based PET applications2 and pyrazole-derived ligands for bioimaging and OLED3, we focus our effort on two groups of bispidine bis-amides, namely, derivatives of ferrocene, which is interesting for producing electro- and photochemical sensor molecules, and pyrazoles, which are promising in designing novel multidentate ligands. We have shown that acyclic bis-ferrocenoyl molecules (Fig, left) exist in an anti-form in crystal, but undergo rapid exchange at room temperature in solution. On the contrary, the macrocyclic derivative (Fig, center) proved to be conformationally stable at room temperature. The co-existence of both anti- and syn-isomers in solution was proved for a series of bis-amides derived from bispidine and pyrazole carbonic acids. In one case we were able to isolate crystals, which contain a unique syn-form (Fig, right). Acknowledgment. This work was supported by RSF (grant 16-13-00114). References 1. Vatsadze, S.Z.; Loginova, Yu.D.; dos Passos Gomes, G.; Alabugin, I.V. Chem. Eur. J. 2017, 23, 3225. 2. Vatsadze, S.Z.; et al. ACS Omega 2016, 1, 854. 3. Utochnikova, V.V., Vatsadze, S.Z.; et al. J. of Lumin. 2018; https://doi.org/10.1016/j.jlumin.2018.05.022