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91.
J.H. van Boom P.M.J. Burgers R. Crea W.C.M.M. Luyten A.B.J. Vink C.B. Reese 《Tetrahedron》1975,31(23):2953-2959
The preparation of three aryl phosphorocyclohexylamidochloridates (7a, 7b and 7c) and an aryl phosphoromorpholidochloridate (8) is described. These aryl phosphoramidochloridates react with 2′,3′-O-methoxymethylene-uridine, -4-N-anisoylcytidine and -6-N-anisoyladenosine (9a, 9b and 9c, respectively), in the presence of the 1-ethylimidazole derivative (11a) to give high yields of the corresponding fully-protected 5′-phosphoramidates (10). Treatment of the latter compounds with aqueous alkali gives the nucleoside 5′-phosphoramidate derivatives (14) which, on mild acidic hydrolysis, give the corresponding unprotected 5′-nucleotides (15) in virtually quantitative yields. Phosphorylation of 2′-O-methoxytetrahydropyranyluridine (12) with 7a and 8, under the same conditions, occurs regiospecifically to give the corresponding 5′-phosphoramidate derivatives (13). The partially-protected dinucleoside phosphate (16b) has been prepared and phosphorylated with 7a to give, after removal of the protecting groups, the dinucleotide (18, pUpU) in high yield. 相似文献
92.
Johan K. Terlouw Peter C. Burgers Helmut Schwarz 《Journal of mass spectrometry : JMS》1980,15(12):599-605
Characterization of some [C4H5O2]+ ions in the gas phase using their collisional activation mass spectra shows that the isomeric ions \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O,} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HC} \equiv {\rm C} - \mathop {{\rm C}({\rm OH}){\rm OCH}_3 }\limits^ + $\end{document} are stable for t?10?5 s. Of these, ions of structure were generated by the site specific gas phase protonation of γ-crotonolactone with isobutane or methanol as chemical ionization reagent gases. These results and those derived from measurements on some 2H, 13C and 18O labelled [C4H5O2]+ product ions, were used to study the mechanisms of unimolecular radical elimination reactions, viz. (1) loss of CH3˙ from [trans-methyl crotonate], (2) loss of H˙ from [methyl acrylate]+˙, (3) loss of H˙ from [cyclopropane carboxylic acid]+˙ and (4) loss of CH3˙ from [1,3-dimethoxypropyne]+˙. It is concluded that none of these losses occur by simple bond cleavage. Mechanisms are presented which account for the observation that the first three reactions yield product ions of structure whereas the ions generated by reaction (4) have structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}. It is further proposed that a minor fraction of the [M-CH3]+ ions from ionized trans-methyl crotonate is generated via a rearrangement process which yields ions of structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_3 {\rm OCH = CH} - \mathop {\rm C}\limits^ + {\rm = O}{\rm .} $\end{document}. 相似文献
93.
Johan K. Terlouw Peter C. Burgers Henk Hommes 《Journal of mass spectrometry : JMS》1979,14(10):574-576
Characterization of [C4H5O]+ ions in the gas phase using their metastable ion and collisional activation spectra shows that the three isomeric ions HC?C? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}H? OCH3, CH3O? \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm + } $\end{document}?C?CH2 and ? OCH3 related to the two stable [C3H3]+ cations [HC?C? CH2]+ and are stable for ≥ 10?5s. In contrast to the formation of cyclopropenium ions, it is found that the methoxy cyclopropenium ion is not generated from acyclic precursor molecules. The small but significant intensity differences found in the collisional activation spectra of [C3H3]+ ions generated from HC?C? CH2I and HC?C? CH2Cl possibly indicate the presence of [C3H3]+ ions of different structures. 相似文献
94.
95.
Gouw JW Burgers PC Trikoupis MA Terlouw JK 《Rapid communications in mass spectrometry : RCM》2002,16(10):905-912
In matrix-assisted laser desorption/ionization (MALDI) analyses of small oligosaccharides a very large increase in sensitivity (by a factor of 1000) may be obtained by introducing a quaternary ammonium center ('quaternization'). Such a quaternary ammonium center may be introduced into the saccharide by reaction with commercially available glycidyltrimethylammonium chloride (GTMA), or by using Girard's reagent T (Naven and Harvey, Rapid Commun. Mass Spectrom. 1996; 10: 829). GTMA reacts with alcohol functionalities, whereas Girard's reagent T is specific for aldehyde and keto groups. Thus reducing saccharides can be derivatized by both GTMA and Girard's reagent T. For example, glucose or cellobiose having a stock concentration of 3 x 10(-5) M (5 microg/mL) produces no sugar-derived signals in conventional MALDI, but their quaternized derivatives, also at 3 x 10(-5) M, yield intense signals, with the matrix-derived signals only being weak. Similar results were obtained for glucosamine. Non-reducing saccharides as well as sugar alcohols can be derivatized using GTMA; thus, although sucrose, raffinose and sorbitol do not react with Girard's reagent T, they all produce intense signals after derivatization with GTMA. An example of the application of these derivatization reactions is provided by the analysis of oligosaccharides in beer. 相似文献
96.
P. C. M. Van Woerkom J. de Bleijser M. de Zwart P. M. J. Burgers und J. C. Leyte 《Colloid and polymer science》1976,254(10):930
Ohne Zusammenfassung 相似文献
97.
98.
From the NIST website and the literature, we have collected the Ionisation Energies (IE) of 3,052 and the Proton Affinities (PA) of 1,670 compounds. For 614 of these, both the IE and PA are known; this enables a study of the relationships between these quantities for a wide variety of molecules. From the IE and PA values, the hydrogen atom affinities (HA) of molecular ions M?+ may also be assessed. The PA may be equated to the heterolytic bond energy of [MH]+ and HA to the homolytic bond energy. Plots of PA versus IE for these substances show (in agreement with earlier studies) that, for many families of molecules, the slope of the ensuing line is less negative than ?1, i.e. changes in the PA are significantly less than the concomitant opposite changes in IE. At one extreme (high PA, low IE) are the metals, their oxides and hydroxides, which show a slope of close to ?1, at the other extreme (low PA, high IE) are the hydrogen halides, methyl halides and noble gases, which show a slope of ca. ?0.3; other molecular categories show intermediate behaviour. One consequence of a slope less negative than ?1 is that the changes in ionic enthalpies of the protonated species more closely follow the changes in the enthalpies of the neutral molecules compared with changes in the ion enthalpies of the corresponding radical cations. This is consistent with findings from ab initio calculations from the literature that the incoming proton, once attached to the molecule, may retain a significant amount of its charge. These collected data allow a comparison of the thermodynamic stability of protonated molecules in terms of their homolytic or heterolytic bond cleavages. Protonated nitriles are particularly stable by virtue of the very large hydrogen atom affinities of their radical cations. 相似文献