Compatibility of thioamides with reverse turn features: synthesis and conformational analysis of two model cyclic pseudopeptides containing thioamides as backbone modifications

Sherman, Douglas B.; Spatola, Arno F.

doi:10.1021/ja00157a064

Cited by 69 publications

(30 citation statements)

References 2 publications

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“…2 So, the incorporation of thioamides to linear peptide chains may exert significant effects in their activity, specificity and/or selectivity. [3][4][5][6] Many publications have reported structural aspects of organic molecules from their mass spectra and some work has been done in regard to tautomerism studies by mass spectrometry. 7 Nevertheless, it is more common for tautomeric equilibrium commonly to be studied by nuclear magnetic resonace (NMR), infrared (IR) and other spectrometric methods.…”

Section: Introductionmentioning

confidence: 99%

Mass Spectrometry as a Tool for the Determination of Heats of Tautomerization of Thioamides in the Gas Phase

Allegretti

Milazzo

Furlong

2005

Eur J Mass Spectrom (Chichester)

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Tautomerism of several thioamides was studied by mass spectrometry. The analysis of the corresponding mass spectra allowed some fragmentations to be assigned to specific tautomers and heats of tautomerization to be determined through temperature effects and electron energy studies. Experimental determinations were strongly supported by theoretical calculations. AM1 semi-empirical results indicate that the thioamide-thioimidol equilibrium can be studied by mass spectrometry. Also, additional evidence was obtained regarding tautomerism occurrence between neutral species.

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Section: Introductionmentioning

confidence: 99%

Mass Spectrometry as a Tool for the Determination of Heats of Tautomerization of Thioamides in the Gas Phase

Allegretti

Milazzo

Furlong

2005

Eur J Mass Spectrom (Chichester)

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“…It is known from syntheses of a-thiopeptides that the necessary N-Boc and Me-ester deprotections are not trivial: the thioamide group can undergo both acidand base-catalyzed hydrolysis 21 ). Still, successful Boc cleavages with CF 3 CO 2 H (TFA) [29], HCl [54], or, preferably SnCl 4 [64] have been reported. Also, reaction conditions appropriate for ester saponification, avoiding S/O exchange on a thioamide group in the same molecule, have been described [23] [42] [54].…”

mentioning

confidence: 99%

“…Still, successful Boc cleavages with CF 3 CO 2 H (TFA) [29], HCl [54], or, preferably SnCl 4 [64] have been reported. Also, reaction conditions appropriate for ester saponification, avoiding S/O exchange on a thioamide group in the same molecule, have been described [23] [42] [54]. Furthermore, activation of the CO 2 H group in an a-thiodipeptide is known to cause cyclization to a thioazlactone 22 ) (cf.…”

mentioning

confidence: 99%

β-Thiopeptides: Synthesis, NMR Solution Structure, CD Spectra, and Photochemistry

Sifferlen¹,

Rueping²,

Gademann³

et al. 1999

HCA

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“…15 In fact, the barrier to rotation in substituted thioformamides is large enough that the cis-and trans-isomers are separable by chromatography. 54,55 Peptides containing thioamide bonds have been used as probes of local peptide secondary structures, but introduction of a thioamide group into a peptide linkage can have significant effects; for example, peptide conformations are maintained 56,57 or destabilized 58,59 due to high rotational barriers. It has been shown that peptide bond replaced by the isosteric thioxo peptide bond in Ala-Pro derivative (Ala-w[CS-N]-Pro) exists as a mixture of cis and trans conformation in aqueous solution and was characterized by a low cis/trans isomerization rate.…”

Section: Introductionmentioning

confidence: 99%

Probing the structural and electronic effects to stabilize nonplanar forms of thioamide derivatives: A computational study

Kesharwani

Ganguly

2011

J Comput Chem

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Density functional calculations have been performed to examine the stability of nonplanar conformations of thioamide derivatives. Electrostatic, orbital, and ring strain effects were invoked to stabilize the nonplanar conformations of thioamide systems 2-7. Electrostatic interactions helped to achieve the twisted forms of thioamide derivatives; however, pyramidal forms predicted to be the global minimum. Negative hyperconjugative type interactions enhanced the stability of the twisted form 4b when compared with the planar form 4a. The influence of ring strain effect to achieve the twisted form of thioamide was observed with azirine ring. The predictions made with B3LYP/cc-pVDZ+ level of theory was found to be in good agreement with more accurate CBS-QB3 method. The solvent calculations performed with polarized continuum solvation model suggest that the relative stabilities of the nonplanar forms of thioamide derivatives are in general similar to the gas phase results. The importance of hydrogen bonding interactions between the solvent molecules and thioamide derivatives was observed toward the enhanced stability of twisted forms using a combination of explicit solvent molecules and continuum model. The natural bond orbital analysis confirmed the participation of n(N) → π*(C=S) delocalizations in the planar forms and corroborated the earlier reports on larger delocalizations in thioamide systems. Furthermore, the influence of electrostatic and ring strain effects on the amide, natural amides, and selenoamide has also been studied.

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Compatibility of thioamides with reverse turn features: synthesis and conformational analysis of two model cyclic pseudopeptides containing thioamides as backbone modifications

Cited by 69 publications

References 2 publications

Mass Spectrometry as a Tool for the Determination of Heats of Tautomerization of Thioamides in the Gas Phase

Mass Spectrometry as a Tool for the Determination of Heats of Tautomerization of Thioamides in the Gas Phase

β-Thiopeptides: Synthesis, NMR Solution Structure, CD Spectra, and Photochemistry

Probing the structural and electronic effects to stabilize nonplanar forms of thioamide derivatives: A computational study

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