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Lanthionine is a nonproteinogenic amino acid with the chemical formula (HOOC-CH(NH<sub>2</sub>)-CH<sub>2</sub>-S-CH<sub>2</sub>-CH(NH<sub>2</sub>)-COOH). As the monosulfide analog of cystine, lanthionine is composed of two alanine residues that are crosslinked on their β-carbon atoms by a thioether linkage.
In 1941, lanthionine was first isolated from the treatment of wool with sodium carbonate<sup>1</sup> and was first synthesized from cysteine and β-chloroalanine.<sup>2</sup> Lanthionines are found widely in nature and have been isolated from human hair, lactalbumin, and feathers. Lanthionines have also been found in bacterial cell walls and are the components of a group of gene encoded peptide antibiotics called lantibiotics, which includes nisin (a food preservative), subtilin, epidermin (an anti staphylococcus and streptococcus agent), and ancovenin (an enzyme inhibitor).<sup>3,</sup><sup>4</sup>
A variety of syntheses of lanthionine have been published including sulfur extrusion from cystine,<sup>5</sup> ring opening of serine β-lactone,<sup>4</sup> and Michael addition of cysteine to dehydroalanine.<sup>6</sup> The sulfur extrusion method is, however, the only pathway for lanthionine that has been employed in the total synthesis of a lantibiotic.