Amino acids and peptides. Part 19. Synthesis of β-1- and β-2-adamantyl aspartates and their evaluation for peptide synthesis

Abstract

β-1- and β-2-Adamantyl aspartates [H-Asp(O-1-Ada)-OH and H-Asp(O-2-Ada)-OH] have been synthesized and their properties examined. Although the 1-Ada group is labile to TFA, the 2-Ada group is unaffected during TFA treatment, but easily removable by methanesulphonic acid (MSA) at room temperature within 5 min. Both groups are unaffected by treatment with 55% piperidine under conditions which easily cleave the fluoren-9-ylmethoxycarbonyl (Fmoc) group from an α-amino group. Both groups can suppress aspartimide formation as a side reaction under acidic and basic conditions during the synthesis of aspartyl peptides. β-1-or β-2-Adamantyl aspartates may be applicable to solidphase peptide synthesis in combination with Fmoc or Boc as an N^α-protecting group, respectively. Some properties of the aspartimide moiety are described.