Solid-phase synthesis of a β3-icosapeptide containing the homologs of the twenty common proteinaceous amino acids -: Preliminary communication

An icosapeptide, 1, containing the beta(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 beta(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 NIS 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 theta = -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 CD3OH is in progress.