[Leu]6-aureobasidin K 1 is an analog of AbK, in which aIle residue at the sixth position of AbK is replaced by Leu. [Leu]6-AbK 1 was successfully synthesized using a combination of solid- and solution-phase that has a difference with the previous method applied for the synthesis of other aureobasidin analogues, [2S,3S-Hmp]-AbL 2.

A total synthesis of cyclodepsipeptide [Leu]6-aureobasidin K using combination of solid- and solution-phase

The initial condensation event in the nonribosomal biosyn-thesisof thepeptideantibioticsgramicidinSandtyrocidineA takes place between a phenylalanine activating racemase GrsA/TycAand the ®rst proline-activatingmodule ofGrsB/ TycB. Recently we established a minimalin vitro model system for NRPS with recombinant His6-tagged GrsA (GrsA Phe-ATE; 127 kDa) and TycB1 (TycB1Pro-CAT; 120 kDa) and demonstrated the catalytic function of the C-domaininTycB1Pro-CAT to form a peptide bond between phenylalanine and proline during diketopiperazine formation (DKP). ...

Recent studies on type II thioesterases (TEIIs) involved in microbial secondary metabolism described a role for these enzymes in the removal of short acyl-S- phosphopantetheine intermediates from misprimed holo-(acyl carrier proteins) and holo-(peptidyl carrier proteins) of polyketide synthases and nonribosomal peptide synthetases. Because of the absence of structural information on this class of enzymes, we performed a mutational analysis on a prototype TEII essential for efficient productionof the lipopeptide antibiotic surfactin (TEIIsrf), which led to identificationof catalytic and structural residues. ...