Editing Peptoid (section)

== Structure ==
Peptoid oligomers are known to be conformationally unstable, due to the flexibility of the main-chain methylene groups and the absence of stabilizing [[hydrogen bond]] interactions along the backbone. Nevertheless, through the choice of appropriate side chains it is possible to form specific steric or electronic interactions that favour the formation of stable secondary structures like helices,<ref name="pmid9539732">{{cite journal | vauthors = Kirshenbaum K, Barron AE, Goldsmith RA, Armand P, Bradley EK, Truong KT, Dill KA, Cohen FE, Zuckermann RN | display-authors = 6 | title = Sequence-specific polypeptoids: a diverse family of heteropolymers with stable secondary structure | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 8 | pages = 4303–4308 | date = April 1998 | pmid = 9539732 | pmc = 22484 | doi = 10.1073/pnas.95.8.4303 | doi-access = free }}</ref> especially peptoids with C-α-branched side chains are known to adopt structure analogous to [[polyproline]] I helix.<ref name="pmid9539733">{{cite journal | vauthors = Armand P, Kirshenbaum K, Goldsmith RA, Farr-Jones S, Barron AE, Truong KT, Dill KA, Mierke DF, Cohen FE, Zuckermann RN, Bradley EK | display-authors = 6 | title = NMR determination of the major solution conformation of a peptoid pentamer with chiral side chains | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 8 | pages = 4309–4314 | date = April 1998 | pmid = 9539733 | pmc = 22485 | doi = 10.1073/pnas.95.8.4309 | doi-access = free }}</ref> Different strategies have been employed to predict and characterize peptoid secondary structure, with the ultimate goal of developing fully folded peptoid protein structures<ref name="pmid22180903">{{cite journal | vauthors = Wetzler M, Barron AE | title = Progress in the de novo design of structured peptoid protein mimics | journal = Biopolymers | volume = 96 | issue = 5 | pages = 556–560 | date = 2011 | pmid = 22180903 | doi = 10.1002/bip.21621 }}</ref>
The cis/trans [[amide bond]] isomerization still leads to a conformational heterogeneity which doesn’t allow for the formation of homogeneous peptoid [[foldamers]].<ref name="pmid18786652">{{cite journal | vauthors = Yoo B, Kirshenbaum K | title = Peptoid architectures: elaboration, actuation, and application | journal = Current Opinion in Chemical Biology | volume = 12 | issue = 6 | pages = 714–721 | date = December 2008 | pmid = 18786652 | doi = 10.1016/j.cbpa.2008.08.015 }}</ref>  Nonetheless, scientists were able to find trans-inducer ''N''-Aryl side chains promoting [[polyproline]] type II helix,<ref name="pmid19049458">{{cite journal | vauthors = Shah NH, Butterfoss GL, Nguyen K, Yoo B, Bonneau R, Rabenstein DL, Kirshenbaum K | title = Oligo(N-aryl glycines): a new twist on structured peptoids | journal = Journal of the American Chemical Society | volume = 130 | issue = 49 | pages = 16622–16632 | date = December 2008 | pmid = 19049458 | doi = 10.1021/ja804580n }}</ref> and strong cis-inducer such as bulky naphtylethyl<ref name="pmid21861531">{{cite journal | vauthors = Stringer JR, Crapster JA, Guzei IA, Blackwell HE | title = Extraordinarily robust polyproline type I peptoid helices generated via the incorporation of α-chiral aromatic N-1-naphthylethyl side chains | journal = Journal of the American Chemical Society | volume = 133 | issue = 39 | pages = 15559–15567 | date = October 2011 | pmid = 21861531 | pmc = 3186054 | doi = 10.1021/ja204755p }}</ref> and tert-butyl<ref name="pmid23590358">{{cite journal | vauthors = Roy O, Caumes C, Esvan Y, Didierjean C, Faure S, Taillefumier C | title = The tert-butyl side chain: a powerful means to lock peptoid amide bonds in the cis conformation | journal = Organic Letters | volume = 15 | issue = 9 | pages = 2246–2249 | date = May 2013 | pmid = 23590358 | doi = 10.1021/ol400820y }}</ref> side chains. It was also found that n→π* interactions can modulate the ratio of cis/trans amide bond conformers,<ref name="pmid19860427">{{cite journal | vauthors = Gorske BC, Stringer JR, Bastian BL, Fowler SA, Blackwell HE | title = New strategies for the design of folded peptoids revealed by a survey of noncovalent interactions in model systems | journal = Journal of the American Chemical Society | volume = 131 | issue = 45 | pages = 16555–16567 | date = November 2009 | pmid = 19860427 | pmc = 3175426 | doi = 10.1021/ja907184g }}</ref> until reaching a complete control of the cis conformer in the peptoid backbone using a functionalizable triazolium side chain.<ref name="pmid22612307">{{cite journal | vauthors = Caumes C, Roy O, Faure S, Taillefumier C | title = The click triazolium peptoid side chain: a strong cis-amide inducer enabling chemical diversity | journal = Journal of the American Chemical Society | volume = 134 | issue = 23 | pages = 9553–9556 | date = June 2012 | pmid = 22612307 | doi = 10.1021/ja302342h }}</ref>