- Isotopically Sensitive Branching as a Tool for Evaluating Multiple Product Formation by Monoterpene Cyclases
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The deuterated substrates geranyl pyrophosphate and geranyl pyrophosphate were employed to examine isotopically sensitive branching in the biosynthesis of monoterpene olefin isomers.By this method, (-)-α-pinene and (-)-β-pinene were shown to be synthesized via a common intermediate by a single cyclization enzyme from grand fir (Abies grandis), as were (-)-α-phellandrene and (-)-β-phellandrene by a single cyclase from lodgepole pine (Pinus contorta).Kinetic isotope effects were determined for the various deprotonations leading to the pinenes and phellandrenes.Key Words: Isotopically sensitive branching, monoterpene biosynthesis, monoterpene cyclase, resin biosynthesis, kinetic isotope effect.
- Wagschal, Kurt,Savage, Thomas J.,Croteau, Rodney
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- Temperature Controls Guest Uptake and Release from Zn4L4 Tetrahedra
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We report the preparation of triazatruxene-faced tetrahedral cage 1, which exhibits two diastereomeric configurations (T1 and T2) that differ in the handedness of the ligand faces relative to that of the octahedrally coordinated metal centers. At lower temperatures, T1 is favored, whereas T2 predominates at higher temperatures. Host-guest studies show that T1 binds small aliphatic guests, whereas T2 binds larger aromatic molecules, with these changes in binding preference resulting from differences in cavity size and degree of enclosure. Thus, by a change in temperature the cage system can be triggered to eject one bound guest and take up another.
- Zhang, Dawei,Ronson, Tanya K.,Güryel, Songül,Thoburn, John D.,Wales, David J.,Nitschke, Jonathan R.
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- Acorenone B: AChE and BChE inhibitor as a major compound of the essential oil distilled from the ecuadorian species niphogeton dissecta (Benth.) J.F. macbr
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This study investigated the chemical composition, physical proprieties, biological activity, and enantiomeric analysis of the essential oil from the aerial parts of Niphogeton dissecta (culantrillo del cerro) from Ecuador, obtained by steam distillation. The qualitative and quantitative analysis of the essential oil was realized by gas chromatographic and spectroscopic techniques (GC-MS and GC-FID). Acorenone B was identified by GC-MS and NMR experiments. The enantiomeric distribution of some constituents has been assessed by enantio-GC through the use of a chiral cyclodextrin-based capillary column. We identified 41 components that accounted for 96.46% of the total analyzed, the major components were acorenone B (41.01%) and (E)-β-ocimene (29.64%). The enantiomeric ratio of (+)/(-)-β-pinene was 86.9:13.1, while the one of (+)/(-)-sabinene was 80.9:19.1. The essential oil showed a weak inhibitory activity, expressed as Minimal Inhibitory Concentration (MIC), against Enterococcus faecalis (MIC 10 mg/mL) and Staphylococcus aureus (MIC 5 mg/mL). Furthermore, it inhibited butyrylcholinesterase with an IC50 value of 11.5 μg/mL. Pure acorenone B showed inhibitory activity against both acetylcholinesterase and butyrylcholinesterase, with IC50 values of 40.8 μg/mL and 10.9 μg/mL, respectively.
- Calva, James,Bec, Nicole,Gilardoni, Gianluca,Larroque, Christian,Cartuche, Luis,Bicchi, Carlo,Montesinos, José Vinicio
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- Oxidation of cyclohexene and α-pinene with O2-H 2 mixture in the presence of supported platinum or palladium catalysts
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Oxidation of cyclohexene and α-pinene with an O2-H 2 mixture in the catalytic systems containing Pt or Pd and heteropoly compounds (HPC) was studied. The main oxidation products are epoxides, allyl alcohols, and ketones. The highest yield of the oxidation products was obtained in the presence of the platinum catalyst in combination with HPC PW11 or PW11Fe. The reaction mechanism was proposed. A relationship between the HPC composition and the nature of intermediates involved in oxidation was examined.
- Kuznetsova,Kuznetsova,Kirillova,Pokrovskii,Detusheva,Ancel,Likholobov
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p. 1544 - 1551
(2007/10/03)
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- The first regio- and diastereoselective synthesis of homochiral perhydroimidazoisoxazoles via the 1,3-dipolar cycloaddition of imidazoline 3-oxides with (1S)-(-)-β-pinene
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The 1,3-dipolar cycloaddition of imidazoline 3-oxides 1 with (1S)-(-)-β-pinene proceeds regio- and diastereoselectively to give homochiral perhydroimidazoisoxazole derivatives 3 in high yields in the cases of imidazoline 3-oxides 1a-e but in low yields in
- Coskun, Necdet,Tat, Fatma Tirli,Gueven, Oezden Oezel
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p. 1463 - 1467
(2007/10/03)
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- Reactions of myrtenylzinc bromide with carbonyl compounds. Regio- and diastereo-selectivity
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The organozinc reagent obtained from (-)-myrtenyl bromide and zinc powder in THF, under ultrasonic conditions, reacts rapidly with ketones and aldehydes furnishing homoallylic alcohols in high yields. The reactions were carried out both with preformed all
- Aukrust, Inger Reidun,Nilsen, Nils Olav,Romming, Christian,Skattebol, Lars
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p. 385 - 390
(2007/10/03)
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- The First Stereoselective Palladium-Catalyzed Cyclocarbonylation of β,γ-Substituted Allylic Alcohols
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β,γ-Substituted allylic alcohols react with CO in the presence of catalytic quantities of palladium acetate and 1,4-bis(diphenylphosphino)butane affording α,β-substituted-γ-butyrolactones in 42-85% isolated yields. The complete stereoselectivity observed
- Brunner, Melanie,Alper, Howard
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p. 7565 - 7568
(2007/10/03)
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- Enantioselective synthesis of chiral liquid crystalline compounds from monoterpenes
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Chiral liquid crystalline compounds 1-9 have been synthesized enantioselectively from monoterpenes. The optical purities of (S)-(-)- and (R)-(+)-perillalcohol (16, 27), (S)-(-)- and (R)-(+)-1-pentyl-4-hydroxymethyl-1-cyclohexene (33, 34) and (2S,5S)-2-pentyl-5-hydroxymethyl-1-cyclohexanone (53) have been determined by 1H NMR analysis using chiral shift reagents. The mesomorphic phases and transition temperatures of compounds 2,3,5,6,7,8 and 9 have been characterized.
- Wang, Qian,Fan, Shi Yan,Wong, Henry N. C.,Li, Zhong,Fung, Bing M.,Twieg, Robert J.,Nguyen, Huu Tinh
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p. 619 - 638
(2007/10/02)
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- SYNTHESIS WITH ORGANOBORANES. I. SYNTHESIS OF ALLYLIC DIETHYLBORANES AND B-ALLYLIC BORINANES VIA METALATION OF OLEFINS. CONTRATHERMODYNAMIC ISOMERIZATION OF OLEFINS
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Allylic organopotassium compounds prepared by metalation of olefins with trimethylsilylmethylpotassium reacted with chlorodiethylborane and b-chloroborinane to give allylic diethylboranes and B-allylic borinanes, respectively.Hydrolysis of these organoboranes proceeding with allylic rearrangement leads to isomerized olefins.In this way, (E,Z)-2-pentene, (Z)-2-heptene, 1-methylcyclohexene and (+)-α-pinene were cleanly transformed into 1-pentene, 1-heptene, methylenecyclohexane and (+)-β-pinene, respectively.Stereochemistry of the addition of myrtenyldiethylborane toformaldehyde and 2-cyclohexenyldiethylborane to 4-t-butylcyclohexanone is described.
- Zaidlewicz, Marek
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p. 139 - 146
(2007/10/02)
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- Thermal Reactions of B-Alkyl-9-borabicyclononane (9-BBN). Evidence for Unusually Facile Dehydroboration with B-Pinanyl-9-BBN
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B-Alkyl-9-BBN compounds undergo a slow olefin-alkyl group exchange when refluxed with an olefin in tetrahydrofuran.The half-life of the process for B-trans-2-methylcyclopentyl- and B-3-methyl-2-butyl-9-BBN is approximately 4 days.However, B-3-pinanyl-9-BBN undergoes an exceptionally rapid olefin-alkyl group exchange with a half-life of less than 10 h.Kinetic and competition experiments support a dehydroboration-hydroboration process.The isomerization of the B-3-pinanyl-9-BBN to B-myrtanyl-9-BBN, which one would expect to accompany such a facile dehydroboration, is not seen until 145 deg C.After 24 h at 165 deg C, the reaction reaches equilibrium with B-trans-myrtanyl-9-BBN as the major product.Treatment of this organoborane with benzaldehyde liberates the rare (+)-β-pinene.The facility with which B-3-pinanyl-9-BBN undergoes dehydroboration has important consequences for asymmetric reductions with this reagent.
- Midland, M. Mark,Petre, Janet E.,Zderic, Stephen A.,Kazubski, Aleksander
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p. 528 - 531
(2007/10/02)
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- Palladium(II)-catalyzed asymmetric oxidative cyclization of 2-allylphenols in the presence of copper(II) acetate and molecular oxygen. Study of the catalysis of the Wacker-type oxidation
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The intramolecular oxidative cyclization of trans-2-(2-butenyl)phenol (2) using (+)-(3,2,10-η-pinene)palladium(II) acetate (1) in the pressure of Cu(OAc)2 and O2 has been studied in order to gain insight into the catalysis of the Wacker-type oxidation. The main results obtained are as follows: (1) the catalytically active Pd(II) species which is different from complex 1 is formed during the reaction, (2) the chiral pinanyl ligand is retained by the catalyst throughout the reaction, and (3) the catalyst consists of copper and palladium linked with an acetate bridge. These results cannot be accounted for by the conventional Wacker-type catalysis involving the reoxidation of palladium(0). A hydroperoxopalladium(II) species coupled with copper(II) acetate is most likely the active catalyst in the present reaction. A mechanism for the enantioselection is also described in comparison with the results obtained by the oxidative cyclization of cis-2-(2-butenyl)phenol.
- Hosokawa, Takahiro,Uno, Tetsuyuki,Inui, Shiro,Murahashi, Shun-Ichi
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p. 2318 - 2323
(2007/10/02)
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