Firefly luciferin active esters

The reaction has fairly strict solvent limitations. Polar aprotic solvents are required, the most usual being the dialkyl phthalates and ethylene glycol dimethyl ether. Other esters are also useful, but acetone, ethanol and halogenated hydrocarbons are much less effective. Some admixture of tert. butanol (up to about 5%) has little effect, but water and other alcohols reduce the quantum yield. It is interesting that the active site of firefly luciferase is known to be particularly hydrophobic. The mechanisms of the two reactions are rather similar in that both require a highly active ester (the adenylate in the case of the firefly). Attack by peroxide occurs in both cases (m mmolecular in the luciferin) and this process may require a non-aqueous environment for maximum efficiency. Some of the most efficient oxalates are listed in Table 2. 

Acridan active esters are particularly efficient, quantum yields in the region of 10% being obtainable. The reaction is entirely analogous to that of firefly and coelenterate luciferins. Dipolar aprotic solvents give the best results and there is good evidence for all the steps shown [21] ... 

In the firefly, the carboxyl group of luciferin is activated. Key features of both compounds include an easily autoxidizable CH group, an activated carbonyl group in juxtaposition, and an oxidation product that is very fluorescent. Studies of the chemistry of the model acridan ester have led to a better understanding of firefly bioluminescence including correct prediction of the structure of the oxidized luciferin product. 

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