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Rearrangement Mechanism (rearrangement + mechanism)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Metal-Promoted Cage Rearrangements in the Tricarbollide Series: Conversion of Ligand Derivatives 7-L- nido -7,8,9-C3B8H10 (L = H3N, tBuH2N, Me2HN) into Neutral 8-R- nido -7,8,9-C3B8H11 (R = H2N, tBuHN, Me2N) Compounds

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2003
Bohumír Grüner
Abstract Deprotonation of the eleven-vertex tricarbaborane zwitterions 7-L- nido -7,8,9-C3B8H10 [1: L = H3N (1a), tBuH2N (1b), Me2HN (1c)], followed by reactions with metal reagents [FeI2, NiCl2, and Ni(C5H5)2] at higher temperatures and in situ acidification, led to the 7 , 8 rearrangement of the N -substituted cage carbon atom to yield a series of 8-amino-substituted derivatives of nido -7,8,9-C3B8H12. These were characterized as 8-R- nido -7,8,9-C3B8H11 [2: R = H2N (2a), tBuHN (2b), Me2N (2c)]. A possible rearrangement mechanism for their formation has been proposed. Deprotonation of compound 2a with proton sponge [PS = 1,8-bis(dimethylaminonaphthalene)] generated the [8- tBuHN- nido -7,8,9-C3B8H10], (2b,) anion, which can be reprotonated to give the original compound 2b and not the tautomeric zwitterion 8- tBuH2N- nido -7,8,9-C3B8H10 (3b). All compounds were characterized by high-field (11B and 1H) NMR and IR spectroscopy, and mass spectrometry. The molecular structures of the neutral carbaborane 2b and its salt PSH+2b,were determined by single-crystal X-ray diffraction analyses. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Theoretical evidence on O,N type smiles rearrangement mechanism: a computational study on the intramolecular cyclization of N -methyl-2-(2-chloropyridin-3-yloxy)-acetamide anion

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2008
Hui Sun
Abstract Smiles rearrangement (SR) falls under a broad category of organic synthesis for many important compounds. A complete understanding toward SR process appeals to the assistance of theoretical research. Herein, by performing quantum chemistry calculations, we give a theoretical evidence for the mechanism of a representative O,N type SR, the intramolecular cyclization of N -methyl-2-(2-chloropyridin-3-yloxy)acetamide anion. It is found that the SR to the ipso -position involves a two-step mechanism and is energetically more favorable than the direct nucleophilic attack by N atom on the ortho -position. The present result rationalizes well the experimentally observed ipso -SR product and provides a consistent picture of the O,N SR process. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Alteration of the disulfide-coupled folding pathway of BPTI by circular permutation

PROTEIN SCIENCE, Issue 5 2004
Grzegorz Bulaj
BPTI, bovine pancreatic trypsin inhibitor; cBPTI, a circular form of BPTI generated by forming a peptide bond between the natural termini; cpBPTI, circularly permuted BPTI. Abstract The kinetics of disulfide-coupled folding and unfolding of four circularly permuted forms of bovine pancreatic trypsin inhibitor (BPTI) were studied and compared with previously published results for both wild-type BPTI and a cyclized form. Each of the permuted proteins was found to be less stable than either the wild-type or circular proteins, by 3,8 kcal/mole. These stability differences were used to estimate effective concentrations of the chain termini in the native proteins, which were 1 mM for the wild-type protein and 2.5 to 4000 M for the permuted forms. The circular permutations increased the rates of unfolding and caused a variety of effects on the kinetics of refolding. For two of the proteins, the rates of a direct disulfide-formation pathway were dramatically increased, making this process as fast or faster than the competing disulfide rearrangement mechanism that predominates in the folding of the wild-type protein. These two permutations break the covalent connectivity among the ,-strands of the native protein, and removal of these constraints appears to facilitate direct formation and reduction of nearby disulfides that are buried in the folded structure. The effects on folding kinetics and mechanism do not appear to be correlated with relative contact order, a measure of overall topological complexity. These observations are consistent with the results of other recent experimental and computational studies suggesting that circular permutation may generally influence folding mechanisms by favoring or disfavoring specific interactions that promote alternative pathways, rather than through effects on the overall topology of the native protein. [source]

Negative ion electrospray ionization mass spectrometry of nucleoside phosphoramidate monoesters: elucidation of novel rearrangement mechanisms by multistage mass spectrometry incorporating in-source deuterium labelling

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 19 2008
Peng-Xiang Xu
Several O-2,,3,-isopropylideneuridine-O-5,-phosphoramidate monoesters were synthesized and analyzed by negative ion electrospray ionization tandem mass spectrometry (ESI-MSn). Two kinds of novel rearrangement reactions were observed due to the difference in the amino acid in the nucleoside phosphoramidate monoesters, and possible mechanisms were proposed. One involves a five-membered cyclic transition state. The other is formation of a stable five-membered ring intermediate by Michael addition. Results were confirmed by tandem mass spectrometry and isotopically labeled hydrogen atoms. Furthermore, the internal hydrogen exchange between active hydrogen and methyl acrylate in the heated capillary of the mass spectrometer was found. The characteristic fragmentation behavior in ESI-MS may be used to monitor this kind of compounds in the biological metabolism. Copyright © 2008 John Wiley & Sons, Ltd. [source]