Solid‐Phase Synthesis of a β 3 ‐Icosapeptide Containing the Homologs of the Twenty Common Proteinaceous Amino Acids. Preliminary Communication

An icosapeptide, 1 , containing the β 3 ‐amino acid residues with the 20 proteinogenic side chains has been assembled by manual solid‐phase synthesis, according to the Fmoc strategy. The sequence was chosen in such a way that a possible 3 14 ‐helical conformation (secondary structure) would be stabilized by salt bridges and have an amphipathic character ( Fig. 1 , a ), and the N‐terminal β 3 hCys would lend itself to thioligations and disulfide formation ( 2 and 3 , in Figs. 1 and 2 ). The products 1 – 3 were pure according to RP‐HPLC, NMR, and MS analysis ( Fig. 1 , b and c, Fig. 2 , c and d , and Fig. 3 ). With due caution, the CD spectra in aqueous solution (pH 7) and in MeOH ( Fig. 4 ), with normalized Cotton effects θ  =−14000 to −16000 [deg⋅cm 2 ⋅dmol −1 ] between 209 and 210 nm, might be taken as an evidence for the presence of 3 14 ‐helical conformations. An evaluation of the data from a 700‐MHz 2D‐NMR measurement of the disulfide 2 in CD 3 OH is in progress.