Ni-to-Ni+ 3-ethylene-bridged partially modified retro-inverso tetrapeptide beta-turn mimetic: design, synthesis, and structural characterization.
A 10-membered heterocyclic ring system 1,3,8-trisubstituted 2,5,7-trioxo-1,4,8-triazadecane that represents a Ni-to-Ni+ 3-ethylene-bridged partially modified retro-inverso tetrapeptide beta-turn mimetic (EBRIT-BTM) has been designed, synthesized, and structurally analyzed. These compounds utilize an ethylene bridge to replace the COi...HNi + 3 10-membered hydrogen bond of standard beta-turns. The N,N'-ethylene-bridged dimer was obtained in 90% yield by reductive alkylation of phenylalanylamide with a tert-butyl N-(9-fluorenylmethyloxycarbonyl),N-(2-formylmethyl)-glycinate. An orthogonal protection strategy and HATU-mediated couplings allowed efficient stepwise additions of monomeric building blocks leading to a N(i)-to-N(i+3)-ethylene-bridged linear precursor: Further elaboration of the linear precursor generated the ethylene-bridged model compounds (16) and (18) (g, gem-diaminoalkyl; m, malonyl; and r, direction-reversed amino acid residue) in 44 and 39% yields, respectively. The structural features of the two EBRIT-BTM compounds were determined using 1H NMR and extensive computer simulations. The results indicate that the 10-membered rings are conformationally constrained with well-defined structural features and that the three amide bonds in the ring are in the trans orientation. The topological arrangement of the residues in the ring system closely resembles a type II' beta-turn. Transformation of CONH(2) in the N-terminal amino acid residue of 16 into NHCOCH3 in 18 resulted in the formation of a hydrogen bond between the NH of gPhe-COCH3 and the C-terminal carboxyl of Gly, initiating an antiparallel beta-sheet. The formulation of the concept applying a minimalistic structural elaboration approach and the synthetic exploration, together with the conformational analysis, offer a new molecular scaffolding system and a true tetrapeptide secondary structure mimetic that can be used to generate peptidomimetics of biological interest.
Han
Yinglin
Y
Department of Medicine, Bone and Mineral Metabolism Unit, Charles A. Dana and Thorndike Laboratories, Beth Israel Deaconess Medical Center-Harvard Medical School, Boston, Massachusetts 02215, USA.
Giragossian
Craig
C
Mierke
Dale F
DF
Chorev
Michael
M
D000478:Alkylation; D002384:Catalysis; D002853:Chromatography, Liquid; D005030:Ethylenes / Q000737:chemistry*; D006572:Heterocyclic Compounds, Bridged-Ring / Q000138:chemical synthesis* / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D018716:Molecular Mimicry; D015394:Molecular Structure; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry*; D011487:Protein Conformation
D005030:Ethylenes; D006572:Heterocyclic Compounds, Bridged-Ring; D009842:Oligopeptides; D010456:Peptides, Cyclic