Development of a new protective group for tryptophan

Sammanfattning: A new protective group for the indole nitrogen of the amino acid tryptophan, the Boc-sarcosinoyl-sarcosinolyl (Boc-Sar-Sar) is described. This protective group shows good stability to the reaction conditions used in solid phase peptide synthesis and is incorporated into the peptide as FmocTrp(BocSarSar)OH. When the peptide is cleaved from the resin with trifluoroacetic acid, the Boc group is simultaneously cleaved and N-terminal nitrogen in the Sar-Sar group is exposed. At low pH this amino group is protonated and thereby the peptide will have higher solubility in aqueous solution. High solubility of the peptide is an important factor for the purification of peptides with reversed phase HPLC. During HPLC purification, the protonated Sar-Sar group will remain on the peptide. When the purified peptide is exposed to pH 7,4 the Sar-Sar group will be cleaved and the peptide will be obtained in its fully deprotected form. This new protective group was used for the synthesis of the antimicrobial peptide gramicidin A, an extremely hydrophobic peptide with no ionizable groups and only a few exposed polar functional groups.