Studies of N-terminal templates for .alpha.-helix formation. Synthesis and conformational analysis of peptide conjugates of (2S,5S,8S,11S)-1-acetyl-1,4-diaza-3-keto-5-carboxy-10-thiatricyclo[2.8.1.04,8]tridecane (Ac-Hel1-OH)
作者:D. S. Kemp、Timothy P. Curran、James G. Boyd、Thomas J. Allen
DOI:10.1021/jo00023a038
日期:1991.11
The following peptide conjugates of the above-named template molecule were prepared: Ac-Hel1-(L-Ala)n-OtBu (n = 1-6) and Ac-Hel1-Sar-(L-Ala)n-OtBu (n = 1-4), where Sar = N-methylglycine. The slowly equilibrating acetamido function causes the H-1 NMR spectrum in CDCl3, CD3CN, DMF-d7, and DMSO-d6 to be split into pairs of resonances corresponding to the s-cis (c) and s-trans (t) amide conformations. The (t)/(c) ratio is formed to be length and solvent dependent for the homoAla oligomers, and the pattern of resonances in the delta-2-3 region of these conjugates is shown to be consistent with a change in conformation at the C-8-C-9 bond concurrent with length-dependent (t) state formation. Study of NOE properties, temperature and solvent dependences of NH chemical shifts, and J-alpha-CH-NH values are shown to be consistent with an assignment of random coil conformations for the (c) states and template-nucleated helical conformations for the (t) states. Solvent-dependent helicity propagation parameters are assigned.