Reaction of Phosphorus Pentasulfide with Organolithiums. An<i>In Situ</i>Reagent for the Preparation of Thiolactams

Goel, O. P.; Krolls, U.

doi:10.1055/s-1987-27871

Cited by 21 publications

(7 citation statements)

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“…15 A large number of other methods to modify P 4 S 10 are known, such as addition of NaHCO 3 or Na 2 CO 3 , R-Li, and (TMS) 2 O and, as recently demonstrated, even silicon oil. [16][17][18][19][20][21][22][23] Some of these procedures are difficult to reproduce. 24 We became intrigued by the overwhelming bias in favor of 2a over 3 when we found that indigo 5 (Figure 2) reacted efficiently with 3 to give 6 in refluxing pyridine, whereas 2a was totally inefficient in this solvent.…”

Section: ' Introductionmentioning

confidence: 99%

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Thionations Using a P₄S₁₀−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone

et al. 2011

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Tetraphosphorus decasulfide (P(4)S(10)) in pyridine has been used as a thionating agent for a long period of time. The moisture-sensitive reagent has now been isolated in crystalline form, and the detailed structure has been determined by X-ray crystallography. The thionating power of this storable reagent has been studied and transferred to solvents such as acetonitrile in which it has proven to be synthetically useful and exceptionally selective. Its properties have been compared with the so-called Lawesson reagent (LR). Particularly interesting are the results from thionations at relatively high temperatures (∼165 °C) in dimethyl sulfone as solvent. Under these conditions, for instance, acridone and 3-acetylindole could quickly be transformed to the corresponding thionated derivatives. Glycylglycine similarly gave piperazinedithione. At these temperatures, LR is inefficient due to rapid decomposition. The thionated products are generally cleaner and more easy to obtain because in the crystalline reagent, impurities which invariably are present in the conventional reagents, P(4)S(10) in pyridine or LR, have been removed.

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Section: ' Introductionmentioning

confidence: 99%

“…This composition, P 4 S 10 ·4C 5 H 5 N, has been retained even in relatively recent work . A large number of other methods to modify P 4 S 10 are known, such as addition of NaHCO 3 or Na 2 CO 3 , R-Li, and (TMS) 2 O and, as recently demonstrated, even silicon oil. − Some of these procedures are difficult to reproduce …”

Section: Introductionmentioning

confidence: 99%

Thionations Using a P₄S₁₀−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone

et al. 2011

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“…Among the strategies employed to reduce the hydrolytic lability of peptides is the replacement of the amide bond with various surrogate functionalities . One of the most synthetically accessible of these functionalities is the thioamide, in which the carbonyl oxygen has been replaced by sulfur, due in part to Lawesson's reagent , and related species − making possible the direct conversion of amides to thioamides. In addition, the controlled insertion of thioamides at specific positions in a peptide sequence has been greatly facilitated through the use of thioacylation techniques. − The resulting “thiopeptides” have been shown to exhibit modified proteolytic stability − and to evidence changes in secondary structure relative to the parent peptides. − This substitution has been shown by Kessler to increase the bioactivity of cyclic hexapeptides, and more recently it has been shown to result in inhibitors of peptidyl-prolyl isomerase …”

Section: Introductionmentioning

confidence: 99%

Conformations of Thioamide-Containing Dipeptides: A Computational Study

Artis

Lipton

1998

J. Am. Chem. Soc.

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Four model dipeptides, Ac-ψ[CSNH]-Gly-NHMe, Ac-Gly-ψ[CSNH]-NHMe, Ac-ψ[CSNH]-Ala-NHMe, and Ac-Ala-ψ[CSNH]-NHMe, each containing a thioamide bond, were studied by high-level ab initio calculations. For each model compound, a conformational potential energy surface was generated by constrained optimization at the HF/6-31G*//HF/6-31G* level of 144 starting geometries, resulting from the systematic variation of the two flexible backbone torsions φ and ψ. Selected regions of each potential energy surface were used as starting points for full geometry optimization at the HF/6-31G*//HF/6-31G* and MP2/6-31G*//MP2/6-31G* levels. The structures and energies of the resulting minima were used to examine the conformational behavior of the model compounds. Whereas the conformations of the C-terminal thioamides were generally close to those of the corresponding peptides, the N-terminal thioamides displayed markedly different conformational behavior. The changes in the conformational profile of thioamide-containing peptides appear to result from a combination of the decreased hydrogen bonding-accepting ability and increased size of sulfur versus oxygen and lengthening of the CS bond in the thioamide as compared to the CO bond in an amide. Insertion of a thioamide linkage into a peptide structure is thus not conformationally neutral and can produce substantial changes in peptide structure, primarily in the residues on the C-terminal side of the thioamide. In addition to the effects on the proteolysis of peptides, the results indicate that this substitution may demonstrate utility as a probe of local peptide secondary structure.

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“…Thioxopeptides represent peptide derivatives in which one or more carbonyl oxygens have been replaced by sulfur. A direct conversion of amides to thioamides can be accomplished by the reaction with Lawesson’s reagent − and related species. − The presence of a thioamide group in the peptide backbone results in several structural changes. The energy barrier for a rotation about the CS–NH bond is 8–12 kJ mol –1 higher than that for the CO–NH bond, due to the more pronounced double-bond character of the thioxopeptide C–N bond .…”

Section: Introductionmentioning

confidence: 99%

A Stable Aminothioketyl Radical in the Gas Phase

2011

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We report the first preparation of a stable aminothioketyl radical, CH(3)C(•)(SH)NHCH(3) (1), by fast electron transfer to protonated thioacetamide in the gas phase. The radical was characterized by neutralization-reionization mass spectrometry and ab initio calculations at high levels of theory. The unimolecular dissociations of 1 were elucidated with deuterium-labeled radicals CH(3)C(•)(SD)NHCH(3) (1a), CH(3)C(•)(SH)NDCH(3) (1b), CH(3)C(•)(SH)NHCD(3) (1c), and CD(3)C(•)(SH)NHCH(3) (1d). The main dissociations of 1 were a highly specific loss of the thiol H atom and a specific loss of the N-methyl group, which were competitive on the potential energy surface of the ground electronic state of the radical. RRKM calculations on the CCSD(T)/aug-cc-pVTZ potential energy surface indicated that the cleavage of the S-H bond in 1 dominated at low internal energies, E(int)< 232 kJ mol(-1). The cleavage of the N-CH(3) bond was calculated to prevail at higher internal energies. Loss of the thiol hydrogen atom can be further enhanced by dissociations originating from the B excited state of 1 when accessed by vertical electron transfer. Hydrogen atom addition to the thioamide sulfur atom is calculated to have an extremely low activation energy that may enable the thioamide group to function as a hydrogen atom trap in peptide radicals. The electronic properties and reactivity of the simple aminothioketyl radical reported here may be extrapolated and applied to elucidate the chemistry of thioxopeptide radicals and cation radicals of interest to protein structure studies.

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Reaction of Phosphorus Pentasulfide with Organolithiums. AnIn SituReagent for the Preparation of Thiolactams

Cited by 21 publications

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Thionations Using a P₄S₁₀−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone

Thionations Using a P₄S₁₀−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone

Conformations of Thioamide-Containing Dipeptides: A Computational Study

A Stable Aminothioketyl Radical in the Gas Phase

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Reaction of Phosphorus Pentasulfide with Organolithiums. AnIn SituReagent for the Preparation of Thiolactams

Cited by 21 publications

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Thionations Using a P4S10−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone

Thionations Using a P4S10−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone

Conformations of Thioamide-Containing Dipeptides: A Computational Study

A Stable Aminothioketyl Radical in the Gas Phase

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Product

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Thionations Using a P₄S₁₀−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone

Thionations Using a P₄S₁₀−Pyridine Complex in Solvents Such as Acetonitrile and Dimethyl Sulfone