84809-71-2Relevant articles and documents
The biosynthesis of branched dialkylpyrazines in myxobacteria
Nawrath, Thorben,Dickschat, Jeroen S.,Kunze, Brigitte,Schulz, Stefan
scheme or table, p. 2129 - 2144 (2011/05/12)
The biosynthesis of the volatiles 2,5- and 2,6-diisopropylpyrazine (2 and 3, resp.) released by the myxobacteria Nannocystis exedens subsp. cinnabarina (Na c29) and Chondromyces crocatus (strains Cm c2 and Cm c5) was studied. Isotopically labeled precursors and proposed pathway intermediates were fed to agar plate cultures of the myxobacteria. Subsequently, the volatiles were collected by use of a closed loop stripping apparatus (CLSA), and incorporation into the pyrazines was followed by GC/MS analysis. [2H 8]Valine was smoothly incorporated into both pyrazines clearly establishing their origin from the amino acid pool. The cyclic dipeptide valine anhydride (16) - a potential intermediate on the biosynthetic pathway to branched dialkylpyrazines - was synthesized containing 2H1 labels in specific positions. Feeding of [2H16]-16 and [2H12]-16 in both valine subunits mainly resulted in the formation of pyrazines derived from only one labeled amino acid, whereas only traces of the expected pyrazines with two labeled subunits were found. To investigate the origin of nitrogen in the pyrazines, a feeding experiment with [15N]valine was performed, resulting in the incorporation of the 15N label. The results contradict a biosynthetic pathway via cyclic dipeptides, but rather point to a pathway on which valine is reduced to valine aldehyde. Its dimerization to 2,5-diisopropyldihydropyrazine 36 and subsequent oxidation results in 2. The proposed biosynthetic pathway neatly fits the results of earlier labeling studies and also explains the formation of the regioisomer 2,6-diisopropylpyrazine 3 by isomerization during the first condensation step of two molecules valine aldehyde. A general biosynthetic pathway to different classes of pyrazines is presented.
Inherent asymmetry of constitutionally equivalent methyl groups in the H/D equilibration of n- and i-C3H7Fe(OH)+ complexes
Trage, Claudia,Zummack, Waltraud,Schroeder, Detlef,Schwarz, Helmut
, p. 2708 - 2710 (2007/10/03)
Transiently formed, constitutionally identical methyl groups remain inequivalent in the course of an n-propyl?isopropyl isomerization (see scheme) operative in Fe÷-mediated dehydration of propanols. The reversibility of the β-hydrogen transfer steps is addressed by examination of the H/D equilibration in metastable complexes of Fe+ with a set of selectivity deuterated propanols by using tandem mass spectrometry.
A combined neutralization-reionization mass spectrometric and theoretical study of oxyallyl and other elusive [C3,H4,O] neutrals
Schalley, Christoph A.,Blanksby, Stephen,Harvey, Jeremy N.,Schroeder, Detlef,Zummack, Waltraud,Bowie, John H.,Schwarz, Helmut
, p. 987 - 1009 (2007/10/03)
Five different anionic [C3′H4′O]?- isomers, i.e. the radical anions of acrolein, acetyl carbene, formyl methyl carbene, methoxy vinylidene, and oxyallyl are generated in an ion beam mass spectrometer and subjected to neutralization-reionization (NR) mass spectrometric experiments including neutral and ion decomposition difference (NIDD) mass spectrometry; the latter allows for the examination of the neutrals' unimolecular reactivity. Further, the anionic, the singlet and triplet neutral, and the cationic [C3′H4′O] ?-/0/?+ potentialenergy surfaces are calculated at the B3LYP/6-311++G(d,p) level of theory. For some species, notably the singlet state of oxyallyl, the theoretical treatment is complemented by G2, CASSCF, and MR-CI calculations. Theory and experiment are in good agreement in that at the neutral stage (i) acrolein does not react within the μsec timescale, (ii) acetyl and formyl methyl carbenes isomerize to methyl ketene, (iii) methoxy vinylidene rearranges to methoxy acetylene, (iv) singlet 1A1 oxyallyl undergoes ring closure to cyclopropanone, and (v) triplet 3B2 oxyallyl may have a lifetime sufficient to survive a NR experiment.
Alkyl Substituent Effect in the Deprotonation of Unsymmetrical Ketones
Johnson, Cris E.,Sannes, Kristin A.,Brauman, John I.
, p. 8827 - 8835 (2007/10/03)
The effect of various degrees of alkyl substitution on the relative rates of deprotonation from the two distinct sites in several unsymmetrical ketones in the gas phase is examined.The infrared multiple photon activation of an appropriately deuterium-labeled alkoxide ion generates the ion-molecule complex for the half-reaction of the bimolecular proton transfer process between an alkyl anion and an unsymmetrical ketone with one deprotonation site selectively deuterated.The resulting products are enolate ions generated by the removal of either a deuteron or a proton and, thus, are distinguishable by mass.The measurement of the enolate ion product ratios, along with an independent measurement of the kinetic isotope effect, allowed the kinetic effect of the alkyl environment on the relative proton transfer rates to be determined.The primary and secondary isotope effects are also estimated from the enolate ion product ratios.By examining the magnitude of the kinetic alkyl effect, the primary isotope effect, and the secondary isotope effect, we learn about the transition state for proton transfer.
The Mechanism of Water Loss from the Oxonium Ions CH3CH2CH2+ O=CH2 and (CH3)2CH+ O=CH2
Bowen, Richard D.,Colburn, Alex W.,Derrick, Peter J.
, p. 147 - 151 (2007/10/02)
Extensive new 2H-labelling results are reported, which pertain to the mechanism of water expulsion from metastable CH3CH2CH2+ O=CH2 and (CH)2CH+ O=CH2 ions.Detailed mechanisms, involving ion-neutral complexes comprising incipient propyl cations coordinated to formaldehyde, propene attached to protonated formaldehyde, or propene and formaldehyde attached to a common proton, are discussed in the light of the labelling data.Loss of positional integrity of the hydrogen and deuterium atoms within the original propyl groups occurs; it is proposed that this takes place via interconversion of the ion-neutral complexes.The crucial step in water elimination appears to be irreversible reorganization of the proton-bound complex (or an ion-neutral complex of protonated formaldehyde and propene) to the open-chain carbonium ion CH3+CHCH2CH2OH.
Elimination of Molecular Hydrogen and Methane from Collision-Activated Alkoxide Negative Ions in the Gas Phase. An ab initio and Isotope Effect Study
Hayes, Roger N.,Sheldon, John C.,Bowie, John H.,Lewis, David E.
, p. 1197 - 1208 (2007/10/02)
Ab initio calculations indicate that the collisional induced losses of molecular hydrogen from the ethoxide negative ion and methane from the t-butoxide negative ion to be stepwise processes in which the key intermediates are -...MeCHO> and -...Me2CO> respectively.Deuterium kinetic isotope effects observed for these and other alkoxide negative ions are in accord with the operation of a stepwise reaction.
