Synthesis, optical properties and in vitro cell viability of novel spiropyrans and their photostationary states

A novel class of spiropyran (SP) was synthesized using a multistep process that involves three key intermediates: (a) diazonium-tetrafluoroborate, (b) hydrazine and (c) indolium iodide. Single crystal X-ray spectroscopy was used to confirm the structure of one of the analogues. The SP analogues were confirmed as being able to isomerize and attain a photostationary state (PSS) upon irradiation with ultraviolet light (UV, 365 nm) in an aqueous environment. UV–visible absorption spectra were recorded to confirm the isomerization properties. The ability of the synthesized compounds to induce growth inhibition of HeLa cervical cancer cells was assessed via the MTT assay after incubation with either the SP or their PSS. The IC 50 values of two PSS ( PSS-2 , 4 ), were observed to be around 14 ± 4 fold lower (26 ± 3 μM) than their corresponding SPs. The most cytotoxic compounds SP-7 and PSS-7 showed the lowest IC 50 values (12 μM). An in vitro tubulin polymerization assay showed that SP - 7 and PSS-7 exhibited the greatest difference in tubulin inhibition relative to unirradiated SP-1 and SP-4 .