Azidoproline Containing Helices:  Stabilization of the Polyproline II Structure by a Functionalizable Group

(4R)- and (4S)-Azidoprolines – Conformation Directing Amino Acids and Sites for Functionalization

“…Furthermore, the observed stabilities of the helical conformations of the oligomers 3R and 3S reflect the s-cis:s-trans conformer ratios of their respective monomers 2R and 2S. [9] …”

“…[9] The two helical conformations have characteristic and well distinguishable CD spectra. A maximum at 226 nm and an intense minimum at 206 nm are indicative of the PPII structure, whereas spectra of PPI helices exhibit maxima at 215 nm and minima around 232 nm.…”

“…We therefore explored whether Azp-containing oligoprolines can be functionalized, for example, by Huisgen's 1,3-dipolar cycloadditions ('click chemistry') [10] and prepared the 18-mer Ac-[Pro-(4R)Azp-Pro] 6 -OH (4) with Azp residues in every third position. [9] Within peptide 4 all azido groups were designed to be positioned on one edge of the PPII helix in aqueous solution as supported by CD and NMR spectroscopy. Under typical click chemistry conditions, the six azido groups within 4 reacted readily with, for example, methyl propiolate to the desired hexatriazole 5 (Scheme 1).…”

Structural Characterization of PPII helical Oligoproline

“…However, in contrast to crystal structures of collagen and several other proteins with PPII-helical domains, crystallization of an oligoproline in a PPII-helical conformation had remained elusive. Our interest in the use of azidoproline-containing oligoprolines as functionalizable scaffolds [3][4][5][6] led us to revisit the crystallization of oligoprolines.…”

Helix Formation of Poly(phenylacetylene)s Bearing Azide Groups through Click Polymer Reaction with Optically Active Acetylenes

“…However, the successful examples where the click reaction was employed for preparing optically active helical polymers are still scarce [5][6][7][8][9][10] despite the attractive applications to chiral materials. [11][12][13][14][15][16][17][18] Recently, we reported a novel approach to the synthesis of diverse optically active polymers using the click reaction.…”