Expedient Synthesis and Characterization of π‑Extended Luciferins

• Published in: Journal of organic chemistry 2024-10, Vol.89 (20), p.14625-14633
• Main Authors: Caldwell, Donald R., Townsend, Katherine M., Kolbaba-Kartchner, Bethany, Hadjian, Tanya, Ivanic, Joseph, Love, Anna C., Malvar, Beatrice, Mills, Jeremy, Prescher, Jennifer A., Schnermann, Martin J.
• Format: Article
• Language: English
• Subjects: Coumarins - chemical synthesis; Coumarins - chemistry; Firefly Luciferin - chemistry; Luciferases - chemistry; Luciferases - metabolism; Luminescent Agents - chemical synthesis; Luminescent Agents - chemistry; Luminescent Measurements; Molecular Structure; Naphthalenes - chemical synthesis; Naphthalenes - chemistry
• ISSN: 0022-3263; 1520-6904; 1520-6904
• DOI: 10.1021/acs.joc.3c01920

Bioluminescence imaging enables the sensitive tracking of cell populations and the visualization of biological processes in living systems. Bioluminescent luciferase/luciferin pairs with far-red and near-infrared emission benefit from the reduced competitive absorption by blood and tissue while also facilitating multiplexing strategies. Luciferins with extended π-systems, such as AkaLumine and recently reported CouLuc-1 and -3, can be used for bioluminescence imaging in this long wavelength regime. Existing synthetic routes to AkaLumine and similar π-extended compounds require a multistep sequence to install the thiazoline heterocycle. Here we detail the development of a two-step strategy for accessing these molecules via a Horner–Wadsworth–Emmons reaction and cysteine condensation sequence from readily available aldehyde starting materials. We detail an improved synthesis of AkaLumine, as well as the corresponding two-carbon homologues, Tri- and Tetra-AkaLumine. We then extended this approach to prepare coumarin- and naphthalene-derived luciferins. These putative luciferins were tested against a panel of luciferases to identify capable emitters. Of these, an easily prepared naphthalene derivative exhibits photon emission on par with that of the broadly used Akaluc/AkaLumine pair with similar emission maxima. Overall, this chemistry provides efficient access to several bioluminescent probes for a variety of imaging applications.