Cysteine racemization during the Fmoc solid phase peptide synthesis of the Nav1.7-selective peptide--protoxin II

J Pept Sci. 2012 Jul;18(7):442-8. doi: 10.1002/psc.2407. Epub 2012 May 17.


Protoxin II is biologically active peptide containing the inhibitory cystine knot motif. A synthetic version of the toxin was generated with standard Fmoc solid phase peptide synthesis. If N-methylmorpholine was used as a base during synthesis of the linear protoxin II, it was found that a significant amount of racemization (approximately 50%) was observed during the process of cysteine residue coupling. This racemization could be suppressed by substituting N-methylmorpholine with 2,4,6-collidine. The crude linear toxin was then air oxidized and purified. Electrophysiological assessment of the synthesized protoxin II confirmed its previously described interactions with voltage-gated sodium channels. Eight other naturally occurring inhibitory knot peptides were also synthesized using this same methodology. The inhibitory potencies of these synthesized toxins on Nav1.7 and Nav1.2 channels are summarized.

MeSH terms

  • Cell Line
  • Cysteine / chemistry*
  • Humans
  • Morpholines / chemistry
  • NAV1.7 Voltage-Gated Sodium Channel / metabolism*
  • Oxidation-Reduction
  • Peptides / chemical synthesis*
  • Peptides / chemistry
  • Peptides / metabolism*
  • Sodium Channel Blockers / chemical synthesis*
  • Sodium Channel Blockers / chemistry
  • Sodium Channel Blockers / metabolism*
  • Solid-Phase Synthesis Techniques*
  • Spider Venoms / chemical synthesis*
  • Spider Venoms / chemistry
  • Spider Venoms / metabolism*
  • Stereoisomerism
  • Substrate Specificity


  • Morpholines
  • NAV1.7 Voltage-Gated Sodium Channel
  • Peptides
  • SCN9A protein, human
  • Sodium Channel Blockers
  • Spider Venoms
  • protoxin II, Thrixopelma pruriens
  • 4-methylmorpholine
  • Cysteine