Tandem P-fragmentation

Schemes 51,52, and 53 outline an extension of the method by the tandem P-fragmentation-cyclization sequence to modify the carbohydrates by the iodosylbenzene-iodine reagent instead of DIB-iodine. Thus, the transformations of D-ribofuranose to 3-O-formyl-a-D-erythrofuranose (Scheme 51), furanose to cyclic ketoses, such as alduronic acid lactones (Scheme 52), and carbohydrates to five- and-six-membered azasugars (Scheme 53) can be achieved. P-Fragmentation of carbohydrate suitably substituted by azide group resulted in the formation of chiral nitriles (Scheme 54). ...

Insertion of Oxygen Atom of Alkoxyl Radical Generated from Fused Cyclic Alcohols by Tandem P-Fragmentation-Cyclization... 

Suginome and collaborators have found that heterocyclic compounds can be formed by insertion of the oxygen atom of alkoxyl radicals into alicyclic compounds the insertion takes place through a tandem P-fragmentation-cyclization sequence. 

The Formation of Fused Furan Rings via Tandem P-Fragmentation-Cyclization of Cyclobutanoxyl Radicals Generated from [2- -2]-Photoadducts Derived from 4-Flydroxycoumarin, 3-(or 4-)-Hydroxy-quinolinone or 2-Hydroxynaphthoquinone withA alkenes... 

Oxasteroids arising from tandem P-fragmentation and cyclization are products in the photolysis of the hypoiodites generated from 3-hydroxy-A -steroids and lead tetraacetate-iodine, as outlined in Scheme 84. The path of the formation of the oxasteroids is outlined in Scheme 85 one-electron oxidation of the intermediate radicals arising from the cyclization of allylic radicals generates the oxonium ions, which trap acetic acid to give the products. 

Boto, A., Betancor, C., Prange, T., and Suarez, E., Fragmentation of alkoxy radicals tandem P-fragmentation-cycloperoxyiodination reaction. Tetrahedron Lett., 33,6687,1992. 

Kaufmann A, Butcher P, Maden K, Widmer M, Giles K, Uria D (2009) Are liquid chromatog-raphy/electrospray tandem quadrupole fragmentation ratios unequivocal confirmation criteria Rapid Commun Mass Spectrom 23 985-998... 

The location of the double bonds in unsaturated glycerophosphocholine (GPC) lipids is made difficult mainly due to the limited amounts of these compounds isolated from cells. When a thin layer of a GPC lipid is exposed to the action of ozone, partial or total ozonization of the unsaturated fatty acid residues may take place, depending on the particular compound being analyzed. The ozonized lipid is dissolved and analyzed by tandem MS. A typical injection into the instrument may be 5 p,L containing 10-20 ng of the lipid. An illustrative example is the ozonized l-stearoyl-2-arachidonoyl-GPC, showing the systematic fragmentation pattern in Scheme 21, typical of the ozonized GPC lipids. Thus, the molecular peak appears increased by one nominal unit (M + H, m/e 1002),... 

For example, the ion of [M-69]+, which is observed in the tandem mass spectra of lycopene, neurosporene, and y-carotene but not a-carotene, p-carotene, lutein, or zeaxanthin, indicates the presence of a terminal acyclic isoprene unit. Elimination of a hydroxyl group or a molecule of water, [M-17]+ or [MH-18]+, from carotenoids such as astaxanthin or zeaxanthin is characteristic of the presence of a hydroxyl group. Also, tandem mass spectrometry can be used to distinguish between isomeric carotenoids such as a-carotene and p-carotene, or lutein and zeaxanthin. For example, the ring of a-carotene containing the double bond that i s not conj ugated to the rest of the polyene chain shows unique retro-Diels-Alder fragmentation to form the ion of [M-56]+. In a similar manner, isomeric lutein and zeaxanthin differ by the... 

Leenheer, J. A., Rostad, C. E., Gates, P. M., Furlong, E. T., and Ferrer, I. (2001). Molecular resolution and fragmentation of fulvic acid by electrospray ionization/multistage tandem mass spectrometry. Anal. Chem. 73,1461-1471. 

Figure 4.7 The ESI-MS/MS fragmentation pathways proposed for OTA by Lau et al. (2000). (Reprinted from Journal of Mass Spectrometry 35, Lau et al., Quantitative determination of ochratoxin A by liquid chromatography/electrospray tandem mass spectrometry, p. 28, Copyright 2000, with permission from John Wiley Sons Ltd)...

P lannitti, MM Sheil, G Wickham. High sensitivity and fragmentation specificity in the analysis of drug-DNA adducts by electrospray tandem mass spectrometry. J Am Chem Soc 119 1490—1491, 1997. 

The conjugate Michael addition of phosphonate-stabilized anions with dimethyl acetylenedicarboxylate has been described. For example, when the sodium salt of dimethyl l-(methoxycarbo-nyljmethylphosphonate is treated with dimethyl acetylenedicarboxylate, an (fij/CZ) mixture of two isomeric P.y-unsaturated phosphonates is isolated in modest yield (37%). ° Addition of enolates derived from diethyl 2-oxocycloalkylphosphonates to dimethyl acetylenedicarboxylate in aprotic conditions results in [n + 2] ring-expanded products in reasonable yields (Scheme 8.50). The reaction proceeds via a tandem Michael-aldol-fragmentation mechanism to give the ring enlarged products. 

Figure 6.15. Positive fragmentation pathways of the monomer catechin retro-Diels-Alder fission (RDA), heterocychc ring fission (HRF), benzofuran-forming fission (BFF), and loss of water molecule. (Reprinted from Li and Deinzer, 2007, Tandem Mass Spectrometry for Sequencing Proanthocyanidins, Analytical Chemistry, 79, p. 1740, with permission from American Chemical Society.)...

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