The Fourier transform infrared spectra are analyzed in the regions of Vs(N-H), amide I, amide II and Vs(C alpha = C beta) bands for a series of Ac-delta Xaa-NHMe, where delta Xaa = delta Ala, (Z)-delta Abu, (Z)-delta Leu, (Z)-delta Phe and delta Val, to determine the predominant solution conformation of these alpha,beta-dehydropeptide-related molecules and the electron distribution perturbation in their amide bonds. The measurements were performed in dichloromethane (DCM). To confirm and rationalize the assignments, the spectra of the respective series of saturated Ac-Xaa-NHMe, recorded in DCM, and the spectra of these two series of unsaturated and saturated compounds, recorded in acetonitrile, were examined. To help interpret the spectroscopic results, the equilibrium geometrical parameters for some selected amides were used. These were optimized with ab initio methods in the 6-31G** basis set. Each of the dehydroamides studied adopted a C5 structure, which in Ac-delta Ala-NHMe is fully extended and accompanied by the strong C5 hydrogen bond. Interaction with the C alpha = C beta bond lessened the amidic resonance within each of the flanking amide groups. The N-terminal C = O bond was noticeably shorter, both amide bonds were longer than the corresponding bonds in the saturated entities and the N-terminal amide system was distorted. Ac-delta Ala-NHMe constituted an exception. Its C-terminal amide bond was shorter than the standard one and both amide systems were prototypically planar.

The Fourier transform infrared spectra of Ac-(E)-deltaAbu-NHMe were analyzed to determine the predominant solution conformation(s) of this (E)-alpha,beta-dehydropeptide-related compound and the electron density perturbation in its amide groups. The measurements were performed in dichloromethane and acetonitrile in the region of mode vs (N-H), amide I, amide II and vs (C(alpha)=Cbeta). The equilibrium geometrical parameters, calculated by a method based on the density functional theory with the B3LYP functional and the 6-31G* basis set, were used to support spectroscopic interpretation and gain some deeper insight into the molecule. The experimental and theoretical data were compared with those of three previously described molecules: isomeric Ac-(Z)-deltaAbu-NHMe, Ac-deltaAla-NHMe, which is deprived of any beta-substituent, and saturated species Ac-Abu-NHMe. The titled compound assumes two conformational states in equilibrium in the DCM solution. One conformer is extended almost fully and like Ac-deltaAla-NHMe is C5 hydrogen-bonded. The other adopts a warped C5 structure similar to that of Ac-(Z)-deltaAbu-NHMe. The C5 hydrogen bond, unlike the H-bond in Ac-deltaAla-NHMe, is disrupted by acetonitrile. The resonance within the N-terminal amide groups in either of the (E)-deltaAbu conformers is not as well developed as the resonance in Ac-Abu-NHMe. However, these N-terminal groups, compared with the other unsaturated compounds, constitute better resonance systems in each conformationally related couple: the C5 hydrogen-bonded Ac-(E)-deltaAbu-NHMe/Ac-deltaAla-NHMe and the warped C5 Ac-(E)-deltaAbu-NHMe/Ac-(Z)-deltaAbu-NHMe. The resonance within the C-terminal groups of the latter couple apparently is similar, but less developed than the resonance in Ac-Abu-NHMe. The electron distribution within the C-terminal group of the hydrogen-bonded C5 (E)-deltaAbu conformer apparently is determined mainly by the electron influx from the C(alpha)=Cbeta double bond.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The Fourier transform infrared spectra are analyzed in the regions of v(s)(N-H), amide I, amide II and v(s)(C-alpha=C-beta) bands for a series of Ac-Delta Xaa-NHMe, where Delta Xaa = Delta Ala, (Z)-Delta Abu, (Z)-Delta Leu, (Z)-Delta Phe and Delta Val, to determine the predominant solution conformation of these alpha,beta-dehydropeptide-related molecules and the electron distribution perturbation in their amide bonds, The measurements were performed in dichloromethane (DCM). To confirm and rationalize the assignments, the spectra of the respective series of saturated Ac-Xaa-NHMe, recorded in DCM, and the spectra of these two series of unsaturated and saturated compounds, recorded in acetonitrile, were examined. To help interpret the spectroscopic results, the equilibrium geometrical parameters for some selected amides were used. These were optimized with ab initio methods in the 6-31G** basis set, Each of the dehydroamides studied adopted a C-5 structure, which in Ac-Delta Ala-NHMe is fully extended and accompanied by the strong C-5 hydrogen bond. Interaction with the C-alpha=C-beta bond lessened the amidic resonance within each of the flanking amide groups. The N-terminal C=O bond was noticeably shorter, both amide bonds were longer than the corresponding bonds in the saturated entities and the N-terminal amide system was distorted, Ac-Delta Ala-NHMe constituted an exception. Its C-terminal amide bond was shorter than the standard one and both amide systems were prototypically planar.

Potentiometric and spectroscopic measurements and theoretical calculations have revealed that alpha,beta-dehydroamino acid residues have a considerable effect on the co-ordination ability of an adjacent amide nitrogen towards Cu2+ ions. Also the side chain of such residues affects the stability constants and, in some cases, the binding mode of short peptides containing alpha,beta-dehydroamino acid residues. The theoretical calculations showed that all dehydroamino acids except alpha,beta-dehydroalanine tend to bend a peptide chain towards a turn conformation. This has a very strong impact on the co-ordination ability of a dehydropeptide ligand.

NiII, ZnII and CoII complexes of α,β-dehydro-dipeptides (containing Gly, Leu, Ala, Val or Phe residues) were studied by potentiometric and spectroscopic methods. Deprotonation and coordination of amide nitrogens occurred in all cases around the physiological pH range. The dipeptides with composition of Xaa-Δ-Ala formed octahedral species, while Gly-Δ-Xaa (Xaa = Leu or Phe) formed square planar bis complexes with NiII.

The synthesis has been described of the series of four alpha,beta-dehydrodipeptides Pro-DELTAAla, Pro-DELTAAbu, DL-Pro-DELTAPhe, and DL-Pro-DELTAVal** to be investigated as ligands for coordinating proton or metal ions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Potentiometric and spectroscopic data have shown that the double bond within dehydro-peptides considerably affects their behaviour as ligands relative to their saturated parents, with proton and copper(II) ions.

(1989). LOWER ALIPHATIC 2-OXOACIDS AND THEIR ETEYL ESTERS FROM ETHYL ESTERS OF 2-HYDROXY ACIDS. Organic Preparations and Procedures International: Vol. 21, No. 1, pp. 75-82.

AbstractThe α‐hydroxy esters (I) are oxidized with chromic acid to produce the α‐keto esters (II).

ChemInformVolume 19, Issue 32 Natural Products ChemInform Abstract: Synthesis of Peptides with α,β-Dehydroamino Acids. Part 6. Synthesis of N-Benzyloxycarbonyl and N-Trifluoroacetyl Dipeptides of α,β-Dehydro-butyrine, -valine, -leucine, and -isoleucine. L. SMELKA, L. SMELKA Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this authorB. RZESZOTARSKA, B. RZESZOTARSKA Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this authorG. PIETRZYNSKI, G. PIETRZYNSKI Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this authorZ. KUBICA, Z. KUBICA Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this author L. SMELKA, L. SMELKA Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this authorB. RZESZOTARSKA, B. RZESZOTARSKA Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this authorG. PIETRZYNSKI, G. PIETRZYNSKI Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this authorZ. KUBICA, Z. KUBICA Inst. Chem., Pedagog. Univ. Opole, PL-45-052 Opole, Pol.Search for more papers by this author First published: August 9, 1988 https://doi.org/10.1002/chin.198832297Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume19, Issue32August 9, 1988 RelatedInformation

AbstractThe removal of amino protecting groups from a series of twelve model Z‐3) or TFA‐dipeptides of dehydroalanine and (Z)‐dehydrophenylalanine was investigated. During this deprotection, peptides with Δ Ala are prone to side reactions to a higher extent than those with Δ Phe. Therefore it is interesting to note that from the Δ Ala peptides, the Z group can be split off in preparative manner with HCO2NH4 in the presence of Pd C (Table 4).