A Versatile Boc Solid Phase Synthesis of Daptomycin and Analogues Using Site Specific, On‐Resin Ozonolysis to Install the Kynurenine Residue

A de novo solid‐phase synthesis of the cyclic lipodepsipeptide daptomycin via Boc chemistry was achieved. The challenging ester bond formation between the nonproteinogenic amino acid kynurenine was achieved by esterification of a threonine residue with a protected tryptophan. Subsequent late‐stage on‐resin ozonolysis, inspired by the biomimetic pathway, afforded the kynurenine residue directly. Synthetic daptomycin possessed potent antimicrobial activity (MIC 100 =1.0 μg mL −1 ) against S. aureus , while five other daptomycin analogues containing ( 2R,3R )‐3‐methylglutamic acid, ( 2S,4S )‐4‐methylglutamic acid or canonical glutamic acid at position twelve prepared using this new methodology were all inactive, clearly establishing that the ( 2S,3R )‐3‐methylglutamic acid plays a key role in the antimicrobial activity of daptomycin.