Synthesis and comparative properties of two amide‐generating resin linkers for use in solid phase peptide synthesis
Well‐characterized resins of high purity are critical for effective solid phase peptide synthesis (SPPS). The quality of commercial (4‐methyl)benzhydrylamine‐resin (MBHA‐resin), used for the synthesis of peptide amides, is not consistent and residual ketone functionalities are frequently present. Such ketone or aldehyde impurities lead to the formation of acylation‐resistant deletion peptides in SPPS. To avoid these undesirable side reactions, we have optimized the preparation of two amide‐generating linkers, which, in combination with aminomethyl‐resin prepared directly from polystyrene resin, serve as alternatives to MBHA‐resin for peptide amide synthesis. Then we have explored their comparative properties in SPPS. Use of sonication in reductive amination facilitated the synthesis of both benzhydrylamine (BHA) and MBHA linkers. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.
A Single Pseudoproline and Microwave Solid Phase Peptide Synthesis Facilitates an Efficient Synthesis of Human Amylin 1–37
A chemical synthesis of the 37 residue polypeptide human amylin using microwave enhanced solid phase peptide chemistry is described. An optimised protocol used only a single pseudoproline derivative, a chemically pure resin and single couplings of all amino acids to deliver non-oxidised amylin in high yield. Oxidation of the crude peptide to form the disulfide bond was accomplished in 20 min using 2,2′-dipyridyl disulfide in dimethyl sulphoxide giving human amylin that was fully functional in a cAMP assay.
Asparagine coupling in Fmoc solid phase peptide synthesis.
To investigate side reactions during the activation of side chain unprotected asparagine in Fmoc-solid phase peptide synthesis the peptide Met-Lys-Asn-Val-Pro-Glu-Pro-Ser was synthesized using different coupling conditions for introduction of the asparagine residue. Asparagine was activated by DCC/HOBt, BOP (Castro's reagent) or introduced as the pentafluorophenyl ester. The resulting peptide products were analyzed by HPLC, mass spectrometry and Edman degradation. In the crude products varying amounts of beta-cyano alanine were found, which had been formed by dehydration of the side chain amide during carboxyl activation of Fmoc-asparagine. A homogeneous peptide was obtained by using either side chain protected asparagine derivatives with BOP mediated activation or by coupling of Fmoc-Asn-OPfp. Fmoc-Asn(Mbh)-OH and Fmoc-Asn(Tmob)-OH were coupled rapidly and without side reactions with BOP. For the side chain protected derivatives the coupling was as fast as that of other Fmoc-amino acid derivatives, whereas couplings of Fmoc-Asn-OH proceed more slowly. However, during acidolytic cleavage both protection groups, Mbh and Tmob, generate carbonium ions which readily alkylate tryptophan residues in a peptide. Tryptophan modification was examined using the model peptide Asn-Trp-Asn-Val-Pro-Glu-Pro-Ser. Alkylation could be reduced by addition of scavengers to the TFA during cleavage and side chain deprotection. A homogeneous peptide containing both, asparagine and tryptophan, was obtained only by coupling of Fmoc-Asn-OPfp.