- Cysteine as a sustainable sulfur reagent for the protecting-group-free synthesis of sulfur-containing amino acids: Biomimetic synthesis of l-ergothioneine in water
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Biomass-derived cysteine was used as a sustainable sulfur source for the synthesis of rare sulfur-containing amino acids, such as l-ergothioneine (4), which might be a new vitamin, and various l- or d-2-thiohistidine compounds. Key in this simple, one-pot two-step procedure in water is a bromine-induced regioselective introduction of cysteine followed by a novel thermal cleavage reaction in the presence of thiols, a safer alternative to hazardous red phosphorus. Besides avoiding hazardous sulfur reagents, the new protecting-group-free approach reduces drastically the total number of steps, compared to described procedures. The main drawback, i.e. handling of liquid bromine as an activating and oxidizing reagent in water, was addressed by evaluating four alternative methods using in situ generation of bromine or HOBr, and first encouraging results are described.
- Erdelmeier, Irene,Daunay, Sylvain,Lebel, Remi,Farescour, Laurence,Yadan, Jean-Claude
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p. 2256 - 2265
(2012/09/08)
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- Synthesis of L-(+)-ergothioneine
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The first synthesis of L-(+)-ergothioneine (1), a rare natural amino acid, is described. The key step is the direct transformation of the imidazole derivative 11 into imidazole-2-thione 12. This reaction consists of the cleavage and the re-formation of imidazole ring (ANRORC) with phenyl chlorothionoformate via a Bamberger-type intermediate. The conditions used are mild enough to preserve the asymmetric center at the 1a-carbon. The release of enantiomerically pure L-ergothioneine (1) from the ammonium derivative 15 was performed under acidic conditions to avoid the very easy racemization of the betaine function. An efficient and high-yield sypthesis of 2-mercapto-L-histidine (2) which uses the new imidazole-2-thione formation reaction is also described.
- Xu,Yadan
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p. 6296 - 6301
(2007/10/03)
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