Bioluminescence imaging is used to monitor biological processes and human diseases in animal models. Firefly luciferase and its substrate D-luciferin are commonly used in preclinical cancer research to study these processes in vivo and in vitro. The light emitted by the reaction of firefly luciferin is maximal at 560 nm, which does not penetrate biological tissue efficiently due to absorbance by melanin and hemoglobin. For better tissue penetration, a more redshifted emission is desirable. Highly conjugated luciferin analogs have proven to emit light in this range; recently, Infra-Luciferin (iLH2) and TokeOni Luciferin (TLH2), have been synthesized and shown to emit maximal bioluminescence at 706 nm and 675 nm, respectively. We designed a luciferin analog, Compound 1, expecting it to emit in the near-infrared due to its extended conjugation and rigid naphthalene-thiazole substructure. Along the multistep synthetic pathway towards Compound 1, most of the intermediates were characterized, but due to small quantities of material, two of the intermediates as well as the final product are not yet fully characterized. The molecular formula of Compound 1, however, was confirmed by HRMS and a clear bioluminescent emission spectrum was observed upon reaction with the enzyme luciferase and ATP. This gives strong evidence that we produced the correct final product. With a luciferase variant, the novel luciferin was found to have maximal emission at 762 nm, which is the longest wavelength ever reported for a luciferin analog. Unfortunately, the activity of Compound 1 was very low compared with luciferin.
Salituro, Leah, "Synthesis and Characterization of a Novel Near-Infrared Luciferin" (2017). Chemistry Honors Papers. 19.
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