Fmoc-Asp(OtBu)-OH [71989-14-5]

N-Fmoc-L-aspartic acid beta-t-butyl ester   >99%

Molecular Weight: 411.4

Fmoc-Asp(OtBu)-OH is the standard Fmoc-protected derivative of aspartic acid used in peptide synthesis. The t-butyl ester of the side chain is readily hydrolyzed in the same conditions used to cleave peptides from Wang resin or Rink amide resin. The t-butyl cations formed in the hydrolysis of the esters can produce byproducts by reattaching to nucleophilic residues in the peptide, so nucleophilic scavengers such as thiophenol and anisole should be added to the cleavage mixture when Fmoc-Asp(OtBu)-OH is utilized.

Fmoc-Asp(OtBu)-OH Side Reactions

The Asp(OtBu) residue can form aspartimide under strong basic conditions.  The aspartimide can open to form either the desired peptide or the beta-peptide.  Backbone protection on the amino acid before Asp will prevent aspartimide formation.  It has been reported that adding a small amount of formic acid to the piperidine solution used for Fmoc removal will suppress aspartimide formation (T. Michaels, et al., Org. Lett., 2012, 14, 5218)