Synthesis of a visibly emissive 9-nitro-2,3-dihydro-1H-pyrimido[1,2-a]quinoxalin-5-amine scaffold with large stokes shift and live cell imaging

We have developed a novel fluorescent scaffold 4 which is a 9-nitro-2,3-dihydro-1H-pyrimido[1,2-a]quinoxalin-5-amine derivative from the reaction between di-tert-butyl but-2-ynedioate and a quinoxaline molecule containing a dimethyl amine side tail in high yield. The synthesis of scaffold 4 involves an sp3 C–N bond cleavage mechanism which is not very common. The scaffolds 4 is emissive in the visible range λem ∼ (517–540) nm with large stokes shifts (5005–6378) cm−1 in ethanol. Laser confocal microscopy of the live HepG2 cells treated with compound 4f shows that it can be used for live cell imaging in nanomolar concentrations.