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Maurizio Speranza - One of the best experts on this subject based on the ideXlab platform.
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regioselectivity in the gas phase nucleophilic attack on o protonated 3 methyl 2 cyclohexen 1 ol and 1 methyl 2 cyclohexen 1 ol
Chemistry: A European Journal, 1996Co-Authors: Emanuela Dezi, Antonietta Lombardozzi, Garbriele Renzi, Adriano Pizzabiocca, Maurizio SperanzaAbstract:Our radiolytic study of the occurrence in the gas phase of concerted SN2′ reactions on several open-chain allylic oxonium ions generated in the gas phase from the attack of gaseous GA+ acids (GA+CnH+5 (n = 1, 2), iC3H+7, and (CH3)2F+) on suitable substrates is now continued with cyclic allylic alcohols, such as 3-methyl-2-cyclohexen-1-ol (1) and 1-methyl-2-cyclohexen-1-ol (2), with both MeOH and NMe3 as neutral nucleophiles. With MeOH as the nucleophile, the substitution reaction exclusively takes place on 1 as the starting compounds, whereas when the substrate is 2 it is accompanied by extensive elimination. With NMe3, only the elimination reaction is observed in the same systems. The analysis of the isomeric distribution of the substitution and elimination products allows definition of the corresponding reaction patterns. As for open-chain oxonium ions, the nucleophilic attack on O-protonated 1 and 2 is preceded by significant intramolecular interconversion. Partial unimolecular dissociation of the same ionic intermediates also takes place. After careful evaluation of the extent of these side processes, it is demonstrated that the O-protonated 1 undergoes the concerted SN2 process with MeOH almost exclusively (≥ 99%). With O-protonated 2, how ever, the concerted SN2′ pathway (84–95%) prevails over the classical SN2 one (6–17%). Concomitant [1,2] (E2) and [1,4] elimination (E2′) pathways involve attack of the selected nucleophiles on the oxonium ions from 1 and 2. Their relative extent (E2′/E2:1.78–1.96 (1); 1.43-1 70 (2)) appears only slightly dependent on the nature of the ionic substrate, the nucleophile (whether MeOH or NMe3), and the leaving group (whether H2O or MeOH). The effects of both intrinsic structural factors and experimental conditions in determining the SN2′/SN2 and E2′/E2 branchings in the selected oxonium ions is discussed and compared with related gas-phase data.
Dean Guo - One of the best experts on this subject based on the ideXlab platform.
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characterization of tanshinones in the roots of salvia miltiorrhiza dan shen by high performance liquid chromatography with electrospray ionization tandem mass spectrometry
Rapid Communications in Mass Spectrometry, 2006Co-Authors: Min Yang, Jianghao Sun, Dean Guo, Aihua Liu, Shuhong GuanAbstract:The qualitative analysis of tanshinones in the roots of Salvia miltiorrhiza (Dan-shen in Chinese) was performed using high-performance liquid chromatography with electrospray ionization tandem mass spectrometry (ESI-MS(n)). Tanshinones are the major bioactive constituents of Dan-shen, which is used in China for the treatment of haematological abnormalities and cardiovascular diseases. The ESI-MS(n) fragmentation behavior of tanshinones was investigated. For tanshinones with the tanshinone I nucleus, the fragmentation was triggered by loss of a molecule of CO except bearing a substituent at C17 or C18, followed by sequential eliminations of CO. If C(15-16) was a saturated bond, the fragmentation was triggered by elimination of a molecule of H2O. For tanshinones with the tanshinone IIA nucleus, the fragmentation was triggered by loss of a molecule of H2O, followed by successive eliminations of CO. Ions corresponding to loss of a molecule of propylene (Delta m = 42) were also observed. Moreover, when C(15-16) was a saturated bond, ions corresponding to losses of CH3, H2O and propylene were more abundant. If no D-ring existed, the presence of isopropyl resulted in an elimination of a molecule of H2O with an adjacent CO or OH. In addition, the extension of the pi-conjugation in the A-ring (especially at C(1-2)) induced the fragmentation by loss of a molecule of CO. These fragmentation rules were applied to the identification of tanshinones in a chloroform/methanol (3:7) extract of Dan-shen, which was separated on a C18 column with gradient elution. A total of 27 tanshinones were identified, including five new constituents. The established method could be used for the sensitive and rapid identification of tanshinones in the Dan-shen drug and its pharmaceutical preparations.
Emanuela Dezi - One of the best experts on this subject based on the ideXlab platform.
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regioselectivity in the gas phase nucleophilic attack on o protonated 3 methyl 2 cyclohexen 1 ol and 1 methyl 2 cyclohexen 1 ol
Chemistry: A European Journal, 1996Co-Authors: Emanuela Dezi, Antonietta Lombardozzi, Garbriele Renzi, Adriano Pizzabiocca, Maurizio SperanzaAbstract:Our radiolytic study of the occurrence in the gas phase of concerted SN2′ reactions on several open-chain allylic oxonium ions generated in the gas phase from the attack of gaseous GA+ acids (GA+CnH+5 (n = 1, 2), iC3H+7, and (CH3)2F+) on suitable substrates is now continued with cyclic allylic alcohols, such as 3-methyl-2-cyclohexen-1-ol (1) and 1-methyl-2-cyclohexen-1-ol (2), with both MeOH and NMe3 as neutral nucleophiles. With MeOH as the nucleophile, the substitution reaction exclusively takes place on 1 as the starting compounds, whereas when the substrate is 2 it is accompanied by extensive elimination. With NMe3, only the elimination reaction is observed in the same systems. The analysis of the isomeric distribution of the substitution and elimination products allows definition of the corresponding reaction patterns. As for open-chain oxonium ions, the nucleophilic attack on O-protonated 1 and 2 is preceded by significant intramolecular interconversion. Partial unimolecular dissociation of the same ionic intermediates also takes place. After careful evaluation of the extent of these side processes, it is demonstrated that the O-protonated 1 undergoes the concerted SN2 process with MeOH almost exclusively (≥ 99%). With O-protonated 2, how ever, the concerted SN2′ pathway (84–95%) prevails over the classical SN2 one (6–17%). Concomitant [1,2] (E2) and [1,4] elimination (E2′) pathways involve attack of the selected nucleophiles on the oxonium ions from 1 and 2. Their relative extent (E2′/E2:1.78–1.96 (1); 1.43-1 70 (2)) appears only slightly dependent on the nature of the ionic substrate, the nucleophile (whether MeOH or NMe3), and the leaving group (whether H2O or MeOH). The effects of both intrinsic structural factors and experimental conditions in determining the SN2′/SN2 and E2′/E2 branchings in the selected oxonium ions is discussed and compared with related gas-phase data.
Kenichi Hosoya - One of the best experts on this subject based on the ideXlab platform.
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attenuation of prostaglandin e2 elimination across the mouse blood brain barrier in lipopolysaccharide induced inflammation and additive inhibitory effect of cefmetazole
Fluids and Barriers of the CNS, 2011Co-Authors: Shin Ichi Akanuma, Yasuo Uchida, Sumio Ohtsuki, Masanori Tachikawa, Tetsuya Terasaki, Kenichi HosoyaAbstract:Background Peripheral administration of lipopolysaccharide (LPS) induces inflammation and increases cerebral prostaglandin E2 (PGE2) concentration. PGE2 is eliminated from brain across the blood-brain barrier (BBB) in mice, and this process is inhibited by intracerebral or intravenous pre-administration of anti-inflammatory drugs and antibiotics such as cefmetazole and cefazolin that inhibit multidrug resistance-associated protein 4 (Mrp4/Abcc4)-mediated PGE2 transport. The purpose of this study was to examine the effect of LPS-induced inflammation on PGE2 elimination from brain, and whether antibiotics further inhibit PGE2 elimination in LPS-treated mice.
Garbriele Renzi - One of the best experts on this subject based on the ideXlab platform.
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regioselectivity in the gas phase nucleophilic attack on o protonated 3 methyl 2 cyclohexen 1 ol and 1 methyl 2 cyclohexen 1 ol
Chemistry: A European Journal, 1996Co-Authors: Emanuela Dezi, Antonietta Lombardozzi, Garbriele Renzi, Adriano Pizzabiocca, Maurizio SperanzaAbstract:Our radiolytic study of the occurrence in the gas phase of concerted SN2′ reactions on several open-chain allylic oxonium ions generated in the gas phase from the attack of gaseous GA+ acids (GA+CnH+5 (n = 1, 2), iC3H+7, and (CH3)2F+) on suitable substrates is now continued with cyclic allylic alcohols, such as 3-methyl-2-cyclohexen-1-ol (1) and 1-methyl-2-cyclohexen-1-ol (2), with both MeOH and NMe3 as neutral nucleophiles. With MeOH as the nucleophile, the substitution reaction exclusively takes place on 1 as the starting compounds, whereas when the substrate is 2 it is accompanied by extensive elimination. With NMe3, only the elimination reaction is observed in the same systems. The analysis of the isomeric distribution of the substitution and elimination products allows definition of the corresponding reaction patterns. As for open-chain oxonium ions, the nucleophilic attack on O-protonated 1 and 2 is preceded by significant intramolecular interconversion. Partial unimolecular dissociation of the same ionic intermediates also takes place. After careful evaluation of the extent of these side processes, it is demonstrated that the O-protonated 1 undergoes the concerted SN2 process with MeOH almost exclusively (≥ 99%). With O-protonated 2, how ever, the concerted SN2′ pathway (84–95%) prevails over the classical SN2 one (6–17%). Concomitant [1,2] (E2) and [1,4] elimination (E2′) pathways involve attack of the selected nucleophiles on the oxonium ions from 1 and 2. Their relative extent (E2′/E2:1.78–1.96 (1); 1.43-1 70 (2)) appears only slightly dependent on the nature of the ionic substrate, the nucleophile (whether MeOH or NMe3), and the leaving group (whether H2O or MeOH). The effects of both intrinsic structural factors and experimental conditions in determining the SN2′/SN2 and E2′/E2 branchings in the selected oxonium ions is discussed and compared with related gas-phase data.