Abstract
Firefly luciferin, the substrate for the bioluminescence reaction of luminous beetles, possesses a benzothiazole ring, which is rare in nature. Here, we demonstrate a novel one-pot reaction to give firefly luciferin in a neutral buffer from p-benzoquinone and cysteine without any synthetic reagents or enzymes. The formation of firefly luciferin was low in yield in various neutral buffers, whereas it was inhibited or completely prevented in acidic or basic buffers, in organic solvents, or under a nitrogen atmosphere. Labelling analysis of the firefly luciferin using stable isotopic cysteines showed that the benzothiazole ring was formed via the decarboxylation and carbon-sulfur bond rearrangement of cysteine. These findings imply that the biosynthesis of firefly luciferin can be developed/evolved from the non-enzymatic production of firefly luciferin using common primary biosynthetic units, p-benzoquinone and cysteine.
Highlights
Luciferin, the substrate for the bioluminescence reaction of luminous beetles, possesses a benzothiazole ring, which is rare in nature
McCapra and Razavi reported the chemical synthesis of ethyl 6-hydroxybenzothiazole-2-carboxylate from p-benzoquinone and cysteine ethyl ester hydrochloride in three steps, and suggested that firefly luciferin was biosynthesized from p-benzoquinone and cysteine in nature[13]
Using HPLC with a UV-visible detector, we found a product corresponding to authentic firefly luciferin in the reaction mixture of p-benzoquinone and L-cysteine (1:1) in Tris-HCl (Fig. 1b,c)
Summary
The substrate for the bioluminescence reaction of luminous beetles, possesses a benzothiazole ring, which is rare in nature. Labelling analysis of the firefly luciferin using stable isotopic cysteines showed that the benzothiazole ring was formed via the decarboxylation and carbon-sulfur bond rearrangement of cysteine. These findings imply that the biosynthesis of firefly luciferin can be developed/evolved from the non-enzymatic production of firefly luciferin using common primary biosynthetic units, p-benzoquinone and cysteine. The benzothiazole ring is a common scaffold that can be found in a wide variety of biologically and pharmacologically active compounds[8], it is relatively rare in nature[9] For this reason, research efforts have been directed towards the development of chemical synthetic methods and the clarification of biosynthetic processes of benzothiazole compounds[10,11,12]. Chemical synthesis in water has recently attracted considerable attention as one of the principles of ‘green chemistry’[21], and there have been numerous reports on the successful synthesis of various bioactive compounds based on this concept[22]
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