Synthesis and Bioluminescence of 'V'-Shaped Firefly Luciferin Analogues Based on A Novel Benzobisthiazole Core

The design of pi-extended conjugation 'V'-shaped red shifted bioluminescent D-luciferin analogues based on a novel benzobisthiazole core is described. The divergent synthetic route allowed access to a range of amine donor substituents through an SNAr reaction. In spectroscopic studies, the 'V'-shaped luciferins exhibited narrower optical band gaps, more red-shifted absorption and emission spectra than D-luciferin. Their bioluminescence characteristics were recorded against four different luciferases (PpyLuc, FlucRed, CBR2 and PLR3). With native luciferase PpyLuc, the 'V'-shaped luciferins demonstrated more red-shifted emissions than D-luciferin (lambda(bl)=561 nm) by 60 to 80 nm. In addition, the benzobisthiazole luciferins showed a wide range of bioluminescence spectra from the visible light region (lambda(bl)=500 nm) to the nIR window (>650 nm). The computational results validate the design concept which can be used as a guide for further novel D-luciferin analogues based upon other 'V'-shaped heterocyclic cores.