Lanthionine

Lanthionine is a nonproteinogenic amino acid with the chemical formula (HOOC-CH(NH2)-CH2-S-CH2-CH(NH2)-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.

Background
In 1941, lanthionine was first isolated from the treatment of wool with sodium carbonate and was first synthesized from cysteine and β-chloroalanine. 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).

Preparation
A variety of syntheses of lanthionine have been published including sulfur extrusion from cystine, ring opening of serine β-lactone, and Michael addition of cysteine to dehydroalanine. The sulfur extrusion method is, however, the only pathway for lanthionine that has been employed in the total synthesis of a lantibiotic.