Fig. 4
Simplified scheme, exemplifying chemical synthesis of lanthionine ring using OPLs. a General synthetic scheme of lanthionine ring of lanthipeptide involves dehydration of allyl protected serine or threonine and subsequent Michael addition reaction that couples an allyl protected cysteine to the dehydrated residues to form an OPL or orthogonally protected methyllanthionine respectively (1) The resultant OPL is further coupled to the growing peptide chain on a resin and processed via SPPS to incorporate the desired sequence (Xn). Finally, cyclization reaction involving the encircled groups completes the ring formation, followed by SPPS and so on (2) The Allyl (All) protecting groups, Fmoc fluorenylmethyloxycarbonyl, Pmc penta-methylchromane, Aloc allyloxycarbonyl are essential in the process. The letter R (designated side chain). b Chemical structures of OPLs currently exploited for solid support synthesis of lanthipeptides