A new cyclic thioanhydride derived from chlorophyll a and its aurophilic properties

The need to modify the chlorine macrocycle by additional exocycles is dictated by the desire to increase the stability of the pigment, improve its spectral characteristics, including the shift of the main absorption band to the long-wavelength region, as well as the introduction of chemically active groups for the introduction of other bioactive molecules. Replacing the oxygen atom in the purpurin-18 anhydride exocycle with a sulfur atom can be considered as a bioisosteric substitution, which should not strongly affect the spectral and biological properties of the photosensitizer, but may allow the implementation of new chemical modifications at the periphery of the macrocycle. In this paper, we propose a synthesis pathway for a derivative of naturally occurring chlorin that contains an additional thioanhydride cycle attached to the main macrocycle. We report the spectral characteristics of the compound and demonstrate the possibility of immobilization of chlorin p6 thioanhydride on gold nanoparticles (Au-NP).