Solution and Solid-State Models of Peptide CH···O Hydrogen Bonds

Abstract

Fumaramide derivatives were analyzed in solution by (1)H NMR spectroscopy and in the solid state by X-ray crystallography in order to characterize the formation of CH...O interactions under each condition and to thereby serve as models for these interactions in peptide and protein structure. Solutions of fumaramides at 10 mM in CDCl(3) were titrated with DMSO-d(6), resulting in chemical shifts that moved downfield for the CH groups thought to participate in CH...O=S(CD(3))(2) hydrogen bonds concurrent with NH...O=S(CD(3))(2) hydrogen bonding. In this model, nonparticipating CH groups under the same conditions showed no significant change in chemical shifts between 0.0 and 1.0 M DMSO-d(6) and then moved upfield at higher DMSO-d(6) concentrations. At concentrations above 1.0 M DMSO-d(6), the directed CH...O=S(CD(3))(2) hydrogen bonds provide protection from random DMSO-d(6) contact and prevent the chemical shifts for participating CH groups from moving upfield beyond the original value observed in CDCl(3). X-ray crystal structures identified CH...O=C hydrogen bonds alongside intermolecular NH...O=C hydrogen bonding, a result that supports the solution (1)H NMR spectroscopy results. The solution and solid-state data therefore both provide evidence for the presence of CH...O hydrogen bonds formed concurrent with NH...O hydrogen bonding in these structures. The CH...O=C hydrogen bonds in the X-ray crystal structures are similar to those described for antiparallel beta-sheet structure observed in protein X-ray crystal structures.

A Nonpeptidic Reverse Turn that Promotes Parallel Sheet Structure Stabilized by CH⋅⋅⋅O Hydrogen Bonds in a Cyclopropane γ‐Peptide

“…For 16, the cyclopropane C a H signal at C-2 C is deshielded relative to that at C-2 D , as expected in its role as a hydrogen-bond donor. [27] Similar shift patterns are seen for 13-15.…”

Role of aromatic residues in stabilizing the secondary and tertiary structure of avian pancreatic polypeptide

“…Additionally, a hydrogen bond and three noncanonical CH···O hydrogen bonds [20] between Pro8Gly9 and Ala12 (see Fig. 3) contribute to the fold stability (Table II).…”

Regioselective Hetero-Michael Addition of Oxygen, Sulfur, and Nitrogen­ Nucleophiles to Maleimides Catalyzed by BF3·OEt2

“…Rapid conversion was observed when the reaction was carried out in dichloromethane (92% yield, entry 15) or 1,2-dichloroethane (89% yield, entry 16). The reaction did not work by using DMF, THF, and 1,4-dioxane as solvent (entries [17][18][19]. The above results demonstrated that BF 3 ·OEt 2 is a more effective catalyst in comparison to ZnCl 2 .…”

“…In addition, two single broad peak around 5.8 ppm and 8.4 ppm were assigned to the amide group in the 1 H NMR spectra due to hydrogen bonding (NH-O) interaction of compounds 3g and 3h. 17 On the other hand, thiols have long been known to act as metal catalyst poisons because of their strong coordinating and adsorptive properties, and often rendered the metal catalytic reactions totally ineffective. 18 Therefore, developing a more efficient catalyst system for S-Michael addition remains open to study.…”