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The EIMS fragmentation mechanisms of the sesquiterpenes corvol ethers A and B, epi -cubebol and isodauc-8-en-11-ol

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ABSTRACT

Farnesyl diphosphate (FPP) and all fifteen positional isomers of (13C1)FPP were enzymatically converted by the bacterial terpene cyclases corvol ether synthase from Kitasatospora setae, the epi-cubebol synthase from Streptosporangium roseum, and the isodauc-8-en-11-ol synthase from Streptomyces venezuelae. The enzyme products were analysed by GC–MS and GC–QTOF MS2 and the obtained data were used to delineate the EIMS fragmentation mechanisms of the two sesquiterpene ethers corvol ethers A and B, and the sesquiterpene alcohols epi-cubebol and isodauc-8-en-11-ol.

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PMAs and EIMS fragmentation mechanisms for the fragment ions A) m/z = 207, B) m/z = 189, C) m/z = 163, D) m/z = 149, E) m/z = 95 and F) m/z = 59 of 4. Black carbons contribute fully and red carbons contribute partially to the formation of a fragment ion. α: α-cleavage, rH: hydrogen rearrangement, i: inductive cleavage.
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C5: PMAs and EIMS fragmentation mechanisms for the fragment ions A) m/z = 207, B) m/z = 189, C) m/z = 163, D) m/z = 149, E) m/z = 95 and F) m/z = 59 of 4. Black carbons contribute fully and red carbons contribute partially to the formation of a fragment ion. α: α-cleavage, rH: hydrogen rearrangement, i: inductive cleavage.

Mentions: The mass spectra of unlabelled 4 and its (13C1)-isotopomers are presented in Fig. 4. For the unlabelled compound a small, but visible molecular ion is detected at m/z = 222. The base peak is observed at m/z = 59 and other important fragment ions are detected at m/z = 207, 189, 163, 149 and 95. The PMA207 shows that in contrast to the situation for 3 the fragment ion m/z = 207 arises by cleavage of one of several methyl groups, i.e., either C12, C13 or C14 is lost (Scheme 5). Electron impact ionisation at the oxygen lone pairs of 4 results in the radical cation 4a+· that can undergo one of two possible α-cleavages with loss of C12 or C13 to yield A4+. The alternative ionisation of 4 with loss of an electron from the olefinic double bond leads to 4b+· that may react by hydrogen rearrangement to B4+· and α-cleavage of C14 to C4+. Interestingly, PMA189 demonstrates that the fragment ion m/z = 189 is formed by loss of water and C14, while cleavage of C12 or C13 is prevented by the elimination of water (Scheme 5). After ionisation to 4a+·, a hydrogen rearrangement results in D4+· which enables the loss of C14 by α-cleavage to E4+. A subsequent inductive cleavage with neutral loss of water yields F4+. The last two steps of this mechanism may also proceed in reversed order. Both orders of steps are indeed active for this fragmentation mechanism, as indicated by MS2 analysis of m/z = 207 and m/z = 204 (Figures S9 and S10, Supporting Information File 1).


The EIMS fragmentation mechanisms of the sesquiterpenes corvol ethers A and B, epi -cubebol and isodauc-8-en-11-ol
PMAs and EIMS fragmentation mechanisms for the fragment ions A) m/z = 207, B) m/z = 189, C) m/z = 163, D) m/z = 149, E) m/z = 95 and F) m/z = 59 of 4. Black carbons contribute fully and red carbons contribute partially to the formation of a fragment ion. α: α-cleavage, rH: hydrogen rearrangement, i: inductive cleavage.
© Copyright Policy - Beilstein
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4979868&req=5

C5: PMAs and EIMS fragmentation mechanisms for the fragment ions A) m/z = 207, B) m/z = 189, C) m/z = 163, D) m/z = 149, E) m/z = 95 and F) m/z = 59 of 4. Black carbons contribute fully and red carbons contribute partially to the formation of a fragment ion. α: α-cleavage, rH: hydrogen rearrangement, i: inductive cleavage.
Mentions: The mass spectra of unlabelled 4 and its (13C1)-isotopomers are presented in Fig. 4. For the unlabelled compound a small, but visible molecular ion is detected at m/z = 222. The base peak is observed at m/z = 59 and other important fragment ions are detected at m/z = 207, 189, 163, 149 and 95. The PMA207 shows that in contrast to the situation for 3 the fragment ion m/z = 207 arises by cleavage of one of several methyl groups, i.e., either C12, C13 or C14 is lost (Scheme 5). Electron impact ionisation at the oxygen lone pairs of 4 results in the radical cation 4a+· that can undergo one of two possible α-cleavages with loss of C12 or C13 to yield A4+. The alternative ionisation of 4 with loss of an electron from the olefinic double bond leads to 4b+· that may react by hydrogen rearrangement to B4+· and α-cleavage of C14 to C4+. Interestingly, PMA189 demonstrates that the fragment ion m/z = 189 is formed by loss of water and C14, while cleavage of C12 or C13 is prevented by the elimination of water (Scheme 5). After ionisation to 4a+·, a hydrogen rearrangement results in D4+· which enables the loss of C14 by α-cleavage to E4+. A subsequent inductive cleavage with neutral loss of water yields F4+. The last two steps of this mechanism may also proceed in reversed order. Both orders of steps are indeed active for this fragmentation mechanism, as indicated by MS2 analysis of m/z = 207 and m/z = 204 (Figures S9 and S10, Supporting Information File 1).

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Farnesyl diphosphate (FPP) and all fifteen positional isomers of (13C1)FPP were enzymatically converted by the bacterial terpene cyclases corvol ether synthase from Kitasatospora setae, the epi-cubebol synthase from Streptosporangium roseum, and the isodauc-8-en-11-ol synthase from Streptomyces venezuelae. The enzyme products were analysed by GC–MS and GC–QTOF MS2 and the obtained data were used to delineate the EIMS fragmentation mechanisms of the two sesquiterpene ethers corvol ethers A and B, and the sesquiterpene alcohols epi-cubebol and isodauc-8-en-11-ol.

No MeSH data available.


Related in: MedlinePlus