Investigation of the Cis and Trans Isomers of Sarcosylsarcosine by Nuclear Magnetic Resonance Spectroscopy and Conformational Energy Calculations

Abstract

Nmr of Cis Isomers of Sarcosylsarcosine 535 set of four hydrogen atoms which are involved in bifurcated hydrogen bonds in which the oxygen atoms are in common.Conformations of type B (HGg, HGn, HG12, HG14, HGig, and HG23) also have a pair of intramolecular hydrogen bonds. It does not seem possible to decide from the present experimental data24 which one of these MEC's or a mixture of them is realized in solution.The calculations carried out in this paper should be regarded as the first step of a process to determine the most stable conformation of an isolated molecule in solu-(24) (a) K. D.

Handedness preference and switching of peptide helices. Part II: Helices based on noncodedα‐amino acids

“…Comparable outcomes were seen in a study of intramolecularly catalyzed hydrolysis of a C‐terminal ester by an N‐terminal pyridyl moiety . Several groups studied the conformational preferences of (Sar) n peptides in different solvents using NMR . In the 1 H NMR spectra, the splittings of both the N ‐methyl and methylene signals were analyzed in detail and found to be informative on the local tertiary amide cis / trans situations.…”

“…, has the simplest and one of the least hydrophobic side‐chain chemical structure (a methyl group) among the members of the extremely large family of peptoid building blocks investigated to date (Table ). Beginning in 1971, the results of a large body of computational studies on the preferred conformations of poly‐(Sar) n and Sar derivatives and short homo‐peptides have been reported . Considerable conformational restrictions due to steric overlaps involving the N ‐methyl group, particularly severe for a Sar residue with a preceding cis amide bond, were found.…”

“…The unprotected, charged + H 2 ‐(Sar) 2 ‐O − shows an ‘almost’ extended conformation with the central tertiary amide bond in the cis disposition (cited in Ref. ). Conversely, in the N ‐protected (Sar) 2  peptide, the central tertiary amide bond is trans .…”

Heterocyclic-based peptidomimetics

“…As such, a good deal of effort has gone into preparing peptidomimetics that mimic a cis peptide bond, the simplest examples being N-alkylated peptides [9]. A number of common aromatic heterocycles have also been employed in this context, examples used include pyrrole, tetrazole, triazole and pyrazoles [7].…”

Syntheses, conformation, and reactions of cyclic peptides

“…This fact implies that the complex NMR spectrum arises from a random distribution of cis and trans peptide bonds along the main chain of the cyclic hexapeptide. The four peptide bonds, namely two Sar-Sar and two Gly-Sar peptide bonds, can assume either cis or trans configuration, because N-substituted peptide bond has a lower potential energy of internal rotation (9,10,118). Alternatively, in N-substituted peptide bonds, the minimum potential energy of the trans form has been raised relative to cis, thus reducing the energy difference between them sufficiently to populate the cis form significantly.…”