An entirely fmoc solid phase approach to the synthesis of daptomycin analogs

Abstract

Daptomycin is an important Ca -dependent cyclic lipodepsipeptide antibiotic used to treat serious gram-positive infections. The search for daptomycin analogs with improved activity and their application as tools for studying its mechanism of action has prompted us to develop an entirely Fmoc solid phase approach to the synthesis of daptomycin analogs. Key to the success of this approach was the development of conditions that allowed for the formation of the ester bond on resin-bound peptides consisting of residues 1-10 and the decanoyl lipid tail. The esterification reaction proceeded more efficiently on Tentagel resin as opposed to standard polystyrene resin. This approach was used to synthesize a series of analogs in which each position of Dap-E12-W13, a relatively active daptomycin analog, was individually substituted by alanine. Only positions 2, 6, and 11 were found to be amenable to substitution by alanine in that the corresponding alanine analogs were only 1.5- to 4-fold less active than Dap-E12-W13. We also found that the daptomycin analog, Dap-K6-E12-W13, exhibits in vitro activity approaching that of daptomycin at physiological Ca concentration. Studies with Dap-K6-E12-W13 and model liposomes indicate that this analog interacts with membranes by the same mechanism as daptomycin. This analog is currently being used as a lead for the development daptomycin analogs with improved activity.

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

“…An alternative synthetic route towards daptomycin ( 1 ) was devised to circumvent the direct esterification of the Kyn building block. Inspired by the effective synthesis of Kyn‐containing peptide cyclomontanin B via on‐resin ozonolysis of the corresponding Trp residue to a Kyn residue (Scheme ), and a previous report on the high efficiency of the esterification reaction between Fmoc‐Trp(Boc)‐OH and a resin‐bound threonine‐containing decapeptide, we adopted this combined strategy for the solid‐phase synthesis of native daptomycin ( 1 ) (Scheme ).…”

“…Analogue 17 containing a ( 2S,4S )‐4‐MeGlu residue was therefore synthesized via this approach (Scheme , 5.0 mg, overall yield, 12.3 %) in order to probe the effect of substitution at this position on the antimicrobial activity. The MICs of a daptomycin analogue containing the substitutions of Lys at position six, Glu at position twelve and Trp at position thirteen (Dapt‐Lys 6 /Glu 12 /Trp 13 ) were reported to be quite close to native daptomycin when assayed against B. subtilis and S. aureus strains, indicating that replacement of Orn 6 by Lys 6 was beneficial to the antimicrobial activity. A daptomycin analogue Dapt‐Lys 6 /Glu 12 18 , containing Lys at position six, Glu at position twelve but conserving the Kyn amino acid was thus also prepared (3.5 mg, overall yield, 8.6 %).…”

“…Analogue 17 containing a( 2S,4S)-4-MeGlu residue was therefore synthesized via this approach( Scheme 4, 5.0 mg, overall yield, 12.3 %) in order to probe the effect of substitution at this position on the antimicrobial activity.T he MICs of ad aptomycin analogue containing the substitutions of Lysa tp ositions ix, Glu at position twelve and Trpa tp osition thirteen (Dapt-Lys 6 / Glu 12 /Trp 13 )were reported to be quite close to native daptomycin when assayed against B. subtilis and S. aureus strains, [25] indicatingt hat replacemento fO rn 6 by Lys 6 was beneficial to the antimicrobial activity.Adaptomycin analogue Dapt-Lys 6 /Glu 12 18,c ontaining Lysa tp ositions ix, Glu at position twelve but conserving the Kyn amino acid was thus also prepared (3.5 mg, overall yield, 8.6 %). Due to the fact that mutationo f Kyn 13 to Trp 13 in daptomycin (1)c aused decreased antibacterial activity, [11] the double Kyn substituted analogues Dapt-Kyn 1 / Glu 12 19 containing substitution of Kyn 1 for Trp 1 (3.8 mg, overall yield, 9.4 %) and Dapt-Kyn 1 /Lys 6 /Glu 12 20 (4.8 mg, overall yield, 11.8 %) were also prepared.…”

The calcium-dependent lipopeptide antibiotics: structure, mechanism, & medicinal chemistry

“…More recently, Taylor and coworkers described an concise approach to synthesizing daptomycin entirely on solid support enabling the rapid synthesis of other daptomycin analogues (Scheme 3). 38,39 To enable the total SPPS approach Taylor's group employed an elegant protecting group strategy, including a number of azide masked amino acid building blocks, as well as optimized Fmoc deprotection conditions to protect the sensitive ester linkage.…”

Total synthesis of pseudacyclins A–E by an on-resin head-to-side chain concomitant cyclization-cleavage reaction

“…For example, cycle-tail peptides daptomycin [3][4][5] and polymyxin 6,7 are well-known and widely used antibiotics. 8 Various synthetic methodologies for cycle-tail peptides have been devised; 7,[9][10][11] generally, the final step is a solution macrocyclization between an amine and the C-terminal carboxylic acid. However, this strategy often requires high dilution to counterbalance entropic loss by cyclization.…”