Phosphorus–nitrogen compounds: part 75—design, synthesis, stereogenic and conformational properties of chiral dispiro(N/N)cyclotriphosphazenes: structural analysis and photophysical and bioactivity studies

Abstract

Multiheterocyclic inorganic–organic hybrid phosphazenes have robust inorganic ring systems with the stabilities of the phosphorus nitrogen skeleton and many different substituents bonded to the P atoms. In present study, unsymmetrical dispirocyclotriphosphazenes were prepared due to their potential to depict steric hindrance and electronic rearrangement in creating permanent chirality for certain conformational and configurational isomers. These isomers may have an effect on DNA bindings and activitiy against selected fungi and bacteria, remarkably. Herein, tetrachlorocyclotriphosphazenes (1 and 2) were reacted with 9-ethyl-N-methyl-3-carbazolyl-1,2-diaminoethane (3), 9-ethyl-N-ethyl-3-carbazolyl-1,2-diaminoethane (4) and 9-ethyl-N-methyl-3-carbazolyl-1,3-diaminopropane (5) to give the new unsymmetrical cis/trans-dispirocyclotriphosphazenes, [(ClBz/BzSpiro-6)R1(N3P3)(CzSpiro-n)R2]Cl2 (Cz: Carbazolyl; R1:Me R2:Me or Et; n = 5 or 6; trans 6a–11a and cis 6b–11b). Characterizations, chiralities, and photophysical and biological properties of the new compounds were examined. The molecular and crystal structures of cis-6b, cis-7b, trans-9a, cis-9b, trans-10a and cis-10b were determined by single crystal X-ray crystallography. The chiralities of these compounds with unsymmetrical spiro-architectures were confirmed by X-ray crystallography. These results were further proven by 31P NMR data recorded with the addition of a chiral solvent (CSA). Additionally, circular dichroism (CD) spectra also supported the results. Photophysical measurements indicate that these compounds show emission with lifetimes of approximately 5.6–5.9 ns. In addition, the bioactivities of some isomers were found to be different and quite high against some bacterial and yeast strains. Trans-8a was very active against B. cereus (MBC = 78.1 µM), while cis-6b, trans-9a and cis-9b were very active against the pathogenic yeast C. albicans (MFC = 156.3 µM). Graphical abstract