1. Facile SPS of peptides having C-terminal Asn and Gln
G Breipohl, J Knolle, W Stüber Int J Pept Protein Res. 1990 Mar;35(3):281-3. doi: 10.1111/j.1399-3011.1990.tb00949.x.
Attachment of Fmoc-asparagine or glutamine to p-alkoxybenzyl alcohol type resins has always been difficult and not very effective. A very simple and effective method for the preparation of peptides terminating in asparagine or glutamine is described. The method involves quantitative attachment of Fmoc-Asp-OtBu or Fmoc-Glu-OtBu via their side-chain carboxyl group to a resin functionalized with our TMBPA linker for peptide amides. Peptide synthesis is performed using our standard Fmoc chemistry, and treatment with acid, e.g. TFA/DCM/scavenger mixtures, releases the Asn or Gln peptides.
2. On the use of N-dicyclopropylmethyl aspartyl-glycine synthone for backbone amide protection
René Röder, Petra Henklein, Hardy Weisshoff, Clemens Mügge, Michael Pätzel, Ulrich Schubert, Louis A Carpino, Peter Henklein J Pept Sci. 2010 Jan;16(1):65-70. doi: 10.1002/psc.1196.
To prevent aspartimide formation and related side products in Asp-Xaa, particularly Asp-Gly-containing peptides, usually the 2-hydroxy-4-methoxybenzyl (Hmb) backbone amide protection is applied for peptide synthesis according to the Fmoc-protocols. In the present study, the usefulness of the recently proposed acid-labile dicyclopropylmethyl (Dcpm) protectant was analyzed. Despite the significant steric hindrance of this bulky group, N-terminal H-(Dcpm)Gly-peptides are quantitatively acylated by potent acylating agents, and alternatively the dipeptide Fmoc-Asp(OtBu)-(Dcpm)Gly-OH derivative can be used as a building block. In contrast to the Hmb group, Dcpm is inert toward acylations, but is readily removed in the acid deprotection and resin-cleavage step.
3. New t-butyl based aspartate protecting groups preventing aspartimide formation in Fmoc SPPS
Raymond Behrendt, Simon Huber, Roger Martí, Peter White J Pept Sci. 2015 Aug;21(8):680-7. doi: 10.1002/psc.2790. Epub 2015 Jun 15.
Obtaining homogenous aspartyl-containing peptides via Fmoc/tBu chemistry is often an insurmountable obstacle. A generic solution for this issue utilising an optimised side-chain protection strategy that minimises aspartimide formation would therefore be most desirable. To this end, we developed the following new derivatives: Fmoc-Asp(OEpe)-OH (Epe = 3-ethyl-3-pentyl), Fmoc-Asp(OPhp)-OH (Php = 4-n-propyl-4-heptyl) and Fmoc-Asp(OBno)-OH (Bno = 5-n-butyl-5-nonyl). We have compared their effectiveness against that of Fmoc-Asp(OtBu)-OH and Fmoc-Asp(OMpe)-OH in the well-established scorpion toxin II model peptide variants H-Val-Lys-Asp-Asn/Arg-Tyr-Ile-OH by treatments of the peptidyl resins with the Fmoc removal reagents containing piperidine and DBU at both room and elevated temperatures. The new derivatives proved to be extremely effective in minimising aspartimide by-products in each application.
