- Novel Position-Specific 18O/16O Measurement of Carbohydrates. I. O-3 of Glucose and Confirmation of 18O/16O Heterogeneity at Natural Abundance Levels in Glucose from Starch in a C4 Plant
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The 18O/16O ratio at both molecular and positional levels in the carbohydrates of higher plants is a reliable proxy for the plant growth environment, and a potential indicator of the plant photosynthetic carbon assimilation mode, and its physiological, biochemical and metabolic status. The lack of exploitable nuclear resonance in 18O and 16O and the extremely low 17O abundance make the NMR-based PSIA (position-specific isotopic analysis) a significant challenge. In this Article, an alternative three-step wet chemistry based method for accessing the 18O/16O of glucose O-3 is presented. The O atoms (OH groups) at positions 1, 2, 5, and 6 were first protected by acetonation (converting glucose to 1,2;5,6-di-O-isopropylidene-glucofuranose). The protected glucose was then esterified at O-3 by thionoformylation. Subsequent Barton-McCombie deoxygenation quantitatively removed the O-3 from the protected sugar. Mass balance was then applied to calculate the 18O/16O of O-3 using the isotopic values of the protected sugar before and after the deoxygenation step. The method is innovative in that (i) isolation and purification of individual compounds for 18O by EA/Pyrolysis/IRMS analysis is unnecessary as the reaction mixture can be analyzed on a GC/Pyrolysis/IRMS; (ii) sample quantity is dramatically reduced; and (iii) the approach to access the O-3 isotopic signal can be easily expanded to other positions within glucose and other sugars. It was shown that O-3 is enriched by 12 mUr relative to the molecular average (O-2-O-6) for a glucose of C4 photosynthetic origin. We highlighted the potential applications of the intramolecular O isotopic heterogeneity of glucose this method revealed.
- Ma, Ran,Zhu, Zhenyu,Wang, Bo,Zhao, Yu,Yin, Xijie,Lu, Fengyan,Wang, Ying,Su, Jing,Hocart, Charles H.,Zhou, Youping
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p. 10293 - 10301
(2018/09/06)
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- Tributylgermanium hydride as a replacement for tributyltin hydride in radical reactions
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Tributylgermanium hydride (Bu3GeH) can be used as an alternative to tributyltin hydride (Bu3SnH) as a radical generating reagent with a wide range of radical substrates. Tributylgermanium hydride has several practical advantages over tributyltin hydride, e.g. low toxicity, good stability and much easier work-up of reactions. The reagent can be easily prepared in good yield and stored indefinitely. Suitable substrates include iodides, bromides, activated chlorides, phenyl selenides, tert-nitroalkanes, thiocarbonylimidazolides and Barton esters. Alkyl, vinyl and aryl radicals can be generated in radical reactions including reduction and cyclisation processes. Common radical initiators such as ACCN and triethylborane can be used. The slower rate of hydrogen abstraction by carbon-centred radicals from Bu 3GeH as compared to Bu3SnH facilitates improved cyclisation yields. Polarity reversal catalysis (PRC) with phenylthiol can be used in reactions which generate stable radical intermediates which will not abstract hydrogen from Bu3GeH.
- Bowman, W. Russell,Krintel, Sussie L.,Schilling, Mark B.
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p. 585 - 592
(2007/10/03)
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- The Invention of Radical Reactions. 32. Radical Deoxygenations, Dehalogenations, and Deaminations with Dialkyl Phosphites and Hypophosphorous Acid as Hydrogen Sources
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Reagents, containing a P-H bond, such as dimethyl phosphite, diethyl phosphite, hypophosphorous acid and various salts of hypophosphorous acid are effective radical reducing agents for organic halides, thionoesters, and isocyanides affording high yields of the corresponding hydrocarbons.Reduction of tertiary phenyl selenides and tertiary nitro compounds are not efficient under these conditions.Olefination of 1,2-diols is also accomplished via the corresponding thiocarbonyl derivatives using hypophosphorous acid and triethylamine in the presence of a suitable "sacrifical olefin" im moderate to good yields.
- Barton, Derek H. R.,Jang, Doo Ok,Jaszberenyi, Joseph Cs.
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p. 6838 - 6842
(2007/10/02)
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- The invention of radical reactions. Part XXIX. Radical mono- and dideoxygenations with silanes
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Thionocarbonates and xanthates of primary and secondary alcohols, as well as bis-xanthates of vic-diols are readily deoxygenated to the corresponding hydrocarbons or olefins with phenylsilane, triphenylsilane, and triethylsilane in good yield.
- Barton,Jang,Jaszberenyi Cs.
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p. 2793 - 2804
(2007/10/02)
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- Hypophosphorous acid and its salts: New reagents for radical chain deoxygenation, dehalogenation and deamination
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Thionocarbonates and xanthates of alcohols, bromides, iodides and isonitriles can be transformed to the corresponding hydrocarbons with hypophosphorous acid or its salts in radical chain reactions.
- Barton,Jang,Jaszberenyi
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p. 5709 - 5712
(2007/10/02)
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- The Deoxygenation of NN-Dialkylaminothiocarbonyloxyalkanes
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The title compounds were converted into alkanes in high yield on reduction with potassium and 18-crown-6 in t-butylamine.Thereby both primary and secondary alcohols were conveniently deoxygenated.
- Barrett, Anthony G. M.,Prokopiou, Panayiotis A.,Barton, Derek H. R.
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p. 1510 - 1516
(2007/10/02)
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