4
Tetrahedron Letters
10. Flint, D. G.; Kumita, J. R.; Smart, O. S.; Woolley, G. A. Chem. Biol.
fraction of 10 transitions into the competing α-helix, even at
2002, 9, 391.
high temperatures (S7.12.).
11. Blackwell, H. E.; Grubbs, R. H. Angew. Chem. Int. Ed. 1998, 37, 3281.
12. Ösapay, G.; Taylor, J. W. J. Am. Chem. Soc. 1992, 114, 6966.
13. Shepherd, N. E.; Hoang, H. N.; Abbenante, G.; Fairlie, D. P. J. Am.
Chem. Soc. 2005, 127, 2974.
14. Albert, J. S.; Hamilton, A. D. Biochemistry 1995, 34, 984.
15. Huyghues-Despointes, B.; Scholtz, J. M.; Baldwin, R. L. Protein Sci.
1993, 2, 80.
16. Tsou, L. K.; Tatko, C. D.; Waters, M. L. J. Am. Chem. Soc. 2002, 124,
14917.
17. Ma, M. T.; Hoang, H. N.; Scully, C. C. G.; Appleton, T. G.; Fairlie, D. P.
J. Am. Chem. Soc. 2009, 131, 4505.
Interestingly, the R value is lower in aqueous buffers than in
the helix-promoting solvent TFE (2,2,2-trifluoroethanol)48 (0.49)
(Figure 4b). This means that 10 already has maximum 310-helicty
under aqueous conditions (S7.15). Such behaviour has earlier
been observed in short constrained α-helical peptidomimetics.13
This is also consistent with the mean molar residue ellipticities
(θMRE) of both π→π* and n→π* minima in 10 (-4.23 0.22, -
6.71 0.13 deg·cm²·dmol¯ ¹) being comparable in magnitudes (at
pH 4,7,10 and 288 to 358 K) (S7.6.) to those observed in long
18. Ernst, J. T.; Becerril, J.; Park, H. S.; Yin, H.; Hamilton, A. D. Angew.
Chem. Int. Ed. 2003, 115, 553.
(≥8 residues) peptide with high 310-helicities22,
studied
25, 45, 47
19. Jacobsen, Ø.; Maekawa, H.; Ge, N.-H.; Görbitz, C. H.; Rongved, P.;
Ottersen, O. P.; Amiry-Moghaddam, M.; Klaveness, J. J. Org. Chem. 2011,
76, 1228.
20. Jacobsen, Ø.; Klaveness, J.; Ottersen, O. P.; Amiry-Moghaddam, M. R.;
Rongved, P. Org. Biomol. Chem. 2009, 7, 1599.
under ambient conditions (S7.6). Thus CD data corroborate that
the novel HBS constrains and stabilizes the short peptide 10 in a
robust 310-helical fold, under
temperatures.
a wide range of pH and
21. Blackwell, H. E.; Sadowsky, J. D.; Howard, R. J.; Sampson, J. N.; Chao,
J. A.; Steinmetz, W. E.; O'Leary, D. J.; Grubbs, R. H. J. Org. Chem. 2001,
66, 5291.
22. Boal, A. K.; Guryanov, I.; Moretto, A.; Crisma, M.; Lanni, E. L.; Toniolo,
C.; Grubbs, R. H.; O'Leary, D. J. J. Am. Chem. Soc. 2007, 129, 6986.
23. Madden, M. M.; Vera, C. I. R.; Song, W.; Lin, Q. Chem. Commun. 2009,
5588.
24. Ousaka, N.; Sato, T.; Kuroda, R. J. Am. Chem. Soc. 2008, 130, 463.
25. Biron, Z.; Khare, S.; Samson, A. O.; Hayek, Y.; Naider, F.; Anglister, J.
Biochemistry 2002, 41, 12687.
Finally in order to examine the influence of planarization
rendered by the unique exo-cyclic Moc group in current HBS
model, towards stabilization of 310-helical conformation in the
single unconstrained turn in 10, 11 (cyclo[Ala1-Phe2]-Gly3-Val4-
Glu5-Ipr6) was synthesized by acidic cleavage of the Moc group
from 10 (Scheme 1). In the CD spectrum of 11 (pH 7), both θ
π→π*
and θn→π* are halved (compared to 10) (Figure 4d), indicating a
50% lose in fraction of 310-helical structure in 11. There is
26. Fiori, W. R.; Miick, S. M.; Millhauser, G. L. Biochemistry 1993, 32,
11957.
27. Karle, I. L.; Flippen-Anderson, J. L.; Uma, K.; Balaram, H.; Balaram, P.
Proc. Natl. Acad. Sci. U.S.A. 1989, 86, 765.
28. Shamala, N.; Nagaraj, R.; Balaram, P. Biochem. Biophys. Res. Commun.
1977, 79, 292.
29. Karle, I. L.; Flippen-Anderson, J. L.; Uma, K.; Balaram, H.; Balaram, P.
Proc. Natl. Acad. Sci. U.S.A. 1989, 86, 765.
concomitant large red-shift of λ
(9 nm) which, although is
π→π*
expected since the chiroptic properties of such short helices need
not resemble those of long helices,13 indicates the distortion away
from the canonical 310-helix, that is observed in 10. Thus the
structural constraint from Moc in the current HBS model induces
greater 310-helicity. We are currently investigating the propensity
of this HBS model to propagate the 310-helical structure in longer
natural peptide sequences (>1 unconstrained turn).
30. Toniolo, C.; Polese, A.; Formaggio, F.; Crisma, M.; Kamphuis, J. J. Am.
Chem. Soc. 1996, 118, 2744.
31. Toniolo, C.; Crisma, M.; Moretto, A.; Peggion, C.; Formaggio, F.;
Aleman, C.; Cativiela, C.; Ramakrishnan, C.; Balaram, P. Chem. Eur. J.
2015, 21, 13866.
32. Gessmann, R.; Brückner, H.; Aivaliotis, M.; Petratos, K. J. Pept. Sci.
2015, 21, 476.
33. Formaggio, F.; Crisma, M.; Rossi, P.; Scrimin, P.; Kaptein, B.;
Broxterman, Q. B.; Kamphuis, J.; Toniolo, C. Chem. Eur. J. 2000, 6, 4498.
34. Patgiri, A.; Jochim, A. L.; Arora, P. S. Acc. Chem. Res. 2008, 41, 1289.
35. Wang, D.; Liao, W.; Arora, P. S. Angew. Chem. Int. Ed. 2005, 44, 6525.
36. Chapman, R.; Kulp, I., John L; Patgiri, A.; Kallenbach, N. R.; Bracken,
C.; Arora, P. S. Biochemistry 2008, 47, 4189.
37. Muñoz, V.; Serrano, L. Nat. Struct. Mol. Biol. 1994, 1, 399.
38. Kan, T.; Fukuyama, T. Chem. Commun. 2004, 353.
39. Barlow, D.; Thornton, J. J. Mol. Biol. 1988, 201, 601.
40. Sudha, T.; Vijayakumar, E.; Balaram, P. Chem. Biol. Drug. Des. 1983,
22, 464.
In summary, substitution of an i+3→i peptide hydrogen bond
at the N-terminus of a disordered pentapeptide exclusively based
on coded α-amino acids with a propyl linker and carbamylation
of its N-terminal nitrogen yields the shortest constrained 310-helix
which imposes 310-helicity in a short peptide sequence appended
to its C-terminus. The structural stability of the 310-helix is robust
over a large pH range, as confirmed by NMR and CD spectral
data. Current strategy allows first access to the shortest 310-helix
without need for Cα-tetrasubstituted α-amino acids and with
complete conservation of the constrained sequence, which is
crucial for recognition. Current HBS model will hence find
broader applications as a tool in chemical biology.
References and notes
41. Wishart, D. S.; Sykes, B. D. In [12] Chemical shifts as a tool for structure
determination; Academic Press, 1994; Vol. 239. pp 363.
42. Karplus, M. J. Am. Chem. Soc 1963, 85, 2870.
1. Karle, I.; Flippen‐Anderson, J.; Uma, K.; Balaram, P. Biopolymers 1993,
33, 401.
43. Perutz, M. Nature 1951, 167, 1053.
44. Pal, L.; Basu, G. Protein Eng. 1999, 12, 811.
2. Aravinda, S.; Shamala, N.; Roy, R. S.; Balaram, P. J. Chem. Sci. 2003,
115, 373.
45. Yoder, G.; Polese, A.; Silva, R.; Formaggio, F.; Crisma, M.; Broxterman,
Q. B.; Kamphuis, J.; Toniolo, C.; Keiderling, T. A. J. Am. Chem. Soc. 1997,
119, 10278.
46. Manning, M. C.; Woody, R. W. Biopolymers 1991, 31, 569.
47. Moretto, A.; Formaggio, F.; Kaptein, B.; Broxterman, Q. B.; Wu, L.;
Keiderling, T. A.; Toniolo, C. Peptide Science 2008, 90, 567.
48. Luidens, M. K.; Figge, J.; Breese, K.; Vajda, S. Biopolymers 1996, 39,
367.
3. Enkhbayar, P.; Hikichi, K.; Osaki, M.; Kretsinger, R. H.; Matsushima, N.
Proteins: Struct., Funct., Bioinf. 2006, 64, 691.
4. Toniolo, C.; Benedetti, E. Trends Biochem. Sci. 1991, 16, 350.
5. Vieira-Pires, R. S.; Morais-Cabral, J. H. J. Gen. Physiol. 2010, 136, 585.
6. Schievano, E.; Bisello, A.; Chorev, M.; Bisol, A.; Mammi, S.; Peggion, E.
J. Am. Chem. Soc. 2001, 123, 2743.
7. Cabezas, E.; Satterthwait, A. C. J. Am. Chem. Soc 1999, 121, 3862.
8. Chapman, R. N.; Dimartino, G.; Arora, P. S. J. Am. Chem. Soc. 2004, 126,
12252.
9. Jackson, D. Y.; King, D. S.; Chmielewski, J.; Singh, S.; Schultz, P. G. J.
Am. Chem. Soc. 1991, 113, 9391.