- Total Synthesis of (+)-Erogorgiaene and the Pseudopterosin A?F Aglycone via Enantioselective Cobalt-Catalyzed Hydrovinylation
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Due to their pronounced bioactivity and limited availability from natural resources, metabolites of the soft coral Pseudopterogorgia elisabethae, such as erogorgiaene and the pseudopterosines, represent important target molecules for chemical synthesis. We have now developed a particularly short and efficient route towards these marine diterpenes exploiting an operationally convenient enantioselective cobalt-catalyzed hydrovinylation as the chirogenic step. Other noteworthy C?C bond forming transformations include diastereoselective Lewis acid-mediated cyclizations, a Suzuki coupling and a carbonyl ene reaction. Starting from 4-methyl-styrene the anti-tubercular agent (+)-erogorgiaene (>98 % ee) was prepared in only 7 steps with 46 % overall yield. In addition, the synthesis of the pseudopterosin A aglycone was achieved in 12 steps with 30 % overall yield and, surprisingly, was found to exhibit a similar anti-inflammatory activity (inhibition of LPS-induced NF-κB activation) as a natural mixture of pseudopterosins A?D or iso-pseudopterosin A, prepared by β-D-xylosylation of the synthetic aglycone.
- Movahhed, Sohajl,Westphal, Julia,Kempa, Alexander,Schumacher, Christian Eric,Sperlich, Julia,Neud?rfl, J?rg-Martin,Teusch, Nicole,Hochgürtel, Matthias,Schmalz, Hans-Günther
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supporting information
p. 11574 - 11579
(2021/07/02)
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- Hollow, mesoporous, eutectic Zn1?xMgxO nano-spheres as solid acid-base catalysts for the highly regio-selectiveO-methylation of 1,2-diphenols
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The highly regio-selectiveO-methylation of catechol with dimethyl carbonate (DMC), catalyzed by a solid acid-base catalyst, is an environmentally friendly chemical process for industrial production of guaiacol. However, a guaiacol yield below 84% and high reaction temperature above 280 °C limit its industrial application. Here, hollow, mesoporous Zn1?xMgxO nano-spheres with a eutectic structure, denoted as Zn1?xMgxO HMNSs (x= 0.012-0.089), are facilely fabricatedviathe calcination of Mg2+/Zn2+ion-adsorbing carbon spheres at 500 °C in air. In theO-methylation of catechol with DMC at 180 °C, Zn1?xMgxO HMNSs (x= 0.052) afford guaiacol in 95.5% yield with a complete catechol conversion. Furthermore, 89.0-95.3% mono-ether yields with high 1,2-diphenol conversions (94.5-100%) are also obtained for the other 1,2-diphenols bearing -CH3and -Br groups. Moreover, a plausible mechanism for highly selectiveO-methylation of catechol with DMC is proposed, in which the single-site activation and double-site activation of phenolic hydroxyls by the basic oxygen of Mg-O afford guaiacol and veratrole, respectively.
- Liu, Jie,Ma, Xuebing,Wang, Xuri,Xie, Guangxin,Yin, Zuyong,Zhang, Jianing
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p. 7454 - 7466
(2021/11/23)
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- Efficient heterogeneous palladium-catalyzed transfer hydrogenolysis of benzylic alcohols by formic acid
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An efficient heterogeneous palladium-catalyzed transfer hydrogenolysis- of primary, secondary, and tertiary benzylic alcohols using formic acid as hydrogen source has been developed. The resulting hydrocarbon products were obtained in excellent yields. Moreover, the system exhibits high chemoselectivity, reacting only with the hydroxy groups in the presence of other functional groups, and excellent re-cyclability.
- Afewerki, Samson,Córdova, Armando,Palo-Nieto, Carlos
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supporting information
p. 2330 - 2336
(2020/08/19)
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- Dihydrochelerythrine and its derivatives: Synthesis and their application as potential G-quadruplex DNA stabilizing agents
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A convenient route was envisaged toward the synthesis of dihydrochelerythrine (DHCHL), 4 by intramolecular Suzuki coupling of 2-bromo-N-(2-bromobenzyl)-naphthalen-1-amine derivative 5 via in situ generated arylborane. This compound was converted to (±)-6-acetonyldihydrochelerythrine (ADC), 3 which was then resolved by chiral prep-HPLC. Efficiency of DHCHL for the stabilization of promoter quadruplex DNA structures and a comparison study with the parent natural alkaloid chelerythrine (CHL), 1 was performed. A thorough investigation was carried out to assess the quadruplex binding affinity by using various biophysical and biochemical studies and the binding mode was explained by using molecular modeling and dynamics studies. Results clearly indicate that DHCHL is a strong G-quadruplex stabilizer with affinity similar to that of the parent alkaloid CHL. Compounds ADC and DHCHL were also screened against different human cancer cell lines. Among the cancer cells, (±)-ADC and its enantiomers showed varied (15-48%) inhibition against human colorectal cell line HCT116 and breast cancer cell line MDA-MB-231 albeit low enantio-specificity in the inhibitory effect; whereas DHCHL showed 30% inhibition against A431 cell line only, suggesting the compounds are indeed cancer tissue specific.
- Malhotra, Rajesh,Rarhi, Chhanda,Diveshkumar,Barik, Rajib,D'Cunha, Ruhee,Dhar, Pranab,Kundu, Mrinalkanti,Chattopadhyay, Subrata,Roy, Subho,Basu, Sourav,Pradeepkumar,Hajra, Saumen
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p. 2887 - 2896
(2016/06/13)
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- Useful catalytic enantioselective cationic double annulation reactions initiated at an internal π-bond: Method and applications
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The 1:1 complex of o,o'-dichloro-R-BINOL and SbCl5 initiates the enantioselective cationic polycyclization of polyunsaturated substrates at a predictable π-bond which may be either terminal or, as shown herein, internal. The extension of this powerful construction to internal π-bonds expands the scope of this method and opens up very short pathways to numerous chiral polycyclic molecules, including natural products and their analogues. Especially simple synthetic routes are disclosed that provide access to dysideapalaunic acid, dehydroabietic acid, and epipodocarpic acid and illustrate the value of this enantioselective approach.
- Surendra, Karavadhi,Rajendar, Goreti,Corey
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supporting information
p. 642 - 645
(2014/02/14)
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- Correlating lignin structural features to phase partitioning behavior in a novel aqueous fractionation of softwood Kraft black liquor
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In this work, a set of softwood lignins were recovered from a Kraft black liquor using a novel pH-based fractionation process involving sequential CO 2 acidification and separation of the solvated aqueous lignin fraction. These recovered lignin fractions were characterized with respect to properties that may be responsible for their phase partitioning behavior as well as properties that may render the lignins more suitable for materials applications. Lignin fractions were recovered between a pH range of 12.8 and 9.5 with the bulk of the lignin (90%) recovered between a pH of 11.1 and 10.0. While all the fractions were found to consist primarily of lignin as validated by sample methoxyl content, the first fractions to phase separated were found to be especially enriched in aliphatic extractives and polysaccharides. From the bulk of the lignin that was recovered between a pH of 11.1 and 10.0 a number of noteworthy trends were discernible from the data. Specifically, the phenolic hydroxyl content was found to exhibit a strong negative correlation to the fractionation pH and exhibited a nearly 50% increase with recovery at decreasing pH, while the GPC-estimated molecular weights and 13C NMR-estimated β-O-4 content showed strong positive correlations to the pH at recovery. The aliphatic hydroxyl content exhibited minimal differences between recovery conditions. Overall, these results suggest that this fractionation approach can generate lignin fractions enriched in select physical or structural properties that may be important for their application as feedstocks for renewable chemicals or materials.
- Stoklosa, Ryan J.,Velez, Julian,Kelkar, Shantanu,Saffron, Christopher M.,Thies, Mark C.,Hodge, David B.
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supporting information
p. 2904 - 2912
(2013/10/08)
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- Organotin reagents supported on ionic liquid: highly efficient catalytic free radical reduction of alkyl halides
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Ionic liquid-supported organotin reagents were prepared in good yield and demonstrated a convenient catalytic free radical reduction of alkyl halides. A variety of alkyl and aryl halides could be reduced in high to excellent yields and selectively to afford the desired products with simple work-up procedure.
- Pham, Phuoc Dien,Legoupy, Stéphanie
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experimental part
p. 3780 - 3782
(2009/10/11)
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- Enantioselective synthesis of a trans-7,8-dimethoxycalamenene
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trans-7,8-Dimethoxy-11,12-dehydrocalamenene, a projected intermediate for the total synthesis of marine serrulatane and amphilectane diterpenes, was efficiently synthesized. Starting from a styrene, asymmetric Rh-catalyzed hydroboration using a novel chiral P.P-bidentate ligand afforded an organoboron intermediate (93% ee) which was directly used for C-C bond formation (double homologation, Suzuki coupling). The 1,4-trans-disubstituted tetralin skeleton was selectively formed by a Friedel-Crafts-type catlonic cyclization under strictly aprotic conditions (Me2AlCl) to suppress a remarkable proton-catalyzed disproportionation via diastereoselective hydride transfer.
- Werle, Susen,Fey, Thorsten,Neudoerfl, Joerg M.,Schmalz, Hans-Guenther
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p. 3555 - 3558
(2008/02/12)
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- A solvent-controlled highly efficient Pd-C catalyzed hydrogenolysis of benzaldehydes to methylbenzenes via a novel 'acetal pathway'
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Pd-C catalyzed hydrogenolysis of benzaldehydes to methylbenzenes has been described to proceed via a 'benzenemethanol pathway'. In this article, a novel 'acetal pathway' was first revealed by a systematic study when lower alcohols were used as solvents and a solvent-controlled highly efficient procedure was established.
- Xing, Lixin,Wang, Xinyan,Cheng, Chuanjie,Zhu, Rui,Liu, Bo,Hu, Yuefei
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p. 9382 - 9386
(2008/02/10)
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- Rearrangement of (Polymethoxybenzyl)ammonium N-Methylides
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Reaction of N,N-dimethyl-N-(polymethoxy-substituted benzyl)ammonium iodides 1a-e with cesium fluoride gave polymethoxy-substituted 5--6-methylene-1,3-cyclohexadienes 3 and 5 ( sigmatropic rearrangement products).However, these were quickly hydrolyzed to polymethoxytoluenes 8 during the aqueous workup.The pathway of the hydrolysis of 3 and 5 is discussed.
- Maeda, Yasuhiro,Shirai, Naohiro,Sato, Yoshiro,Tatewaki, Hiroshi
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p. 7897 - 7901
(2007/10/02)
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- Structure-Reactivity Studies and Catalytic Effects in the Photosolvolysis of Methoxy-substituted Benzyl Alcohols
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The photosolvolysis of several methoxy-, dimethoxy-, and hydroxy-substituted benzyl alcohols has been studied in aqueous solution.The primary photochemical event is photodehydroxylation, to give a benzyl cation intermediate, which can be trapped by added external nucleophiles.The reaction is via the singlet excited state, based on observation of fluorescence quenching by hydronium ion in a complementary manner with acid catalysis of reaction observed for several derivatives.Solvent isotope effects on fluorescence efficiency and reaction for (7) and (8) provide additional support of singlet-state reactivity for these compounds.Dimethoxy-substituted alcohols are more reactive than monosubstituted compounds, with quantum yields of methanolysis of up to 0.31 for the most reactive compound, 2,6-dimethoxybenzyl alcohol (8).Using a kinetic argument, the quantum yields of the primary photodehydroxylation process has been estimated to be 1.0 +/- 0.1 for this compound.The results observed for the dimethoxy-substituted derivatives suggest the existence of additivity of substituent effects in these photodehydroxylation reactions.
- Wan, Peter,Chak, Becky
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p. 1751 - 1756
(2007/10/02)
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- LANTHANIDE-INDUCED SHIFTS OF STERICALLY HINDERED AROMATIC o-DIMETHOXY COMPOUNDS: MODEL COMPOUNDS AND o-DIMETHOXYCOUMARINS
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The lanthanide-induced shifts (LIS) of a series of sterically hindered o-dimethoxy compounds, characterized by a 3-substituted 1,2-dimethoxy unit as a structural element, were simulated in model calculations.Development of a generally suitable computational model for aromatic o-dimethoxycompounds allows prediction of relative LIS values for o-dimethoxy complexation.The model was used for several naturally occurring dimethoxycoumarins taking into account the population ratios of the two possible co-ordinating sites in these molecules (o-dimethoxy and lactone carbonyl).
- Hofer, Otmar
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p. 715 - 720
(2007/10/02)
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- Molecular Orbital Calculations and 13C NMR Studies To Explain a Regiospecific Demethylation of 3-Alkyl-1,2-dimethoxybenzenes
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This study was performed to explain a regiospecific demethylation of 3-alkyl-1,2-dimethoxybenzenes.PRDDO-MO calculations show that the low-energy conformation of the carbon of a methoxy group having two ortho neighbors on a benzene ring is located out of the plane of the aromatic ring, whereas a methoxy group with only one ortho neighbor executes restricted rotation in the plane of the ring.The carbon portion of the methoxy group is turned away from the neighboring substituent.These calculations also show that the atomic charge on the oxygen atom in the former caseexceeds that in the latter.The carbon of a methoxy group with two ortho neighbors yields 13C NMR T1 relaxation times longer than those with only one ortho neighbor, also suggesting that the methoxy group with two ortho neighbors is crowded out of the plane of the aromatic ring. 13C NMR chemical shifts of these ortho-substituted methoxybenzenes did not correlate well with shifts predicted from published additive parameters; this again suggests an unusual methoxy group orientation and distribution of electrons.The forced rotation of a methoxy group out of the plane of the benzene ring diminishes the release of electrons from the methoxy group to the benzene ring.The resulting higher atomic charge on the oxygen and the orientation of the oxygen orbitals facilitate complexation with Lewis acids and methoxy group cleavage.
- Jardon, Phillip W.,Vickery, Euin H.,Pahler, Leon F.,Pourahmady, Naser,Mains, Gilbert J.,Eisenbraun, Edmund J.
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p. 2130 - 2135
(2007/10/02)
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- REACTION OF o-BENZOQUINONE BISACETALS WITH ORGANOLITHIUMS. A NOVEL ROUTE TO SUBSTITUTED VERATROLES
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Substituted veratroles were easily obtained by the reaction of o-benzquinone bisacetals with organolithiums.
- Kikuchi, Yoshiyuki,Hasegawa, Yoko,Matsumoto, Masakatsu
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p. 2199 - 2202
(2007/10/02)
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- Catechol O-methyltransferase. 12. Affinity Labeling the Active Site with the Oxidation Products of 5,6-Dihydroxyindole
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5,6-Dihydroxyindole (5,6-DHI) and a series of 4- and/or 7-methylated analogues of 5,6-DHI have been synthesized and evaluated for their ability to inactivate purified liver rat catechol O-methyltransferase (COMT).The inactivation of COMT by these agents could be prevented by excluding oxygen from the incubation mixtures, indicating the necessity for their oxidation to the corresponding aminochromes.Substrate protection studies and kinetic studies suggested that the loss of enzyme activity resulted from the modification of a crucial amino acid residue at the active site of COMT through reaction with the quinoid oxidation products.The COMT inhibitory activity of the 4- and/or 7-methylazed analogues of 5,6-DHI argue against a mechanism involving a 1,4 Michael addition reaction at positions 4 or 7 on the aminochrome.Cnsidering the number of potential eletrophilic centers on the basic aminochrome structure, the site of the reaction might change depending on the aromatic substitution pattern.The preferred pathway of reaction may be determined in part by the juxtaposition of the protein nucleophile to the possible sites of attack on the electrophilic ligand but also in part on the reactivity of the electrophilic site which might change with substitution on the aromatic ring.
- Borchardt, Ronald T.,Bhatia, Pramila
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p. 263 - 271
(2007/10/02)
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- Vesicant Principles of Poison Ivy and Related Plants: Synthesis of the Urushiols, 1,2-Dihydroxy-3-benzene and 1,2-Dihydroxy-3-pentadecylbenzene
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New syntheses of 1,2-dihydroxy-3-benzene (1) and 1,2-dihydroxy-3-pentadecylbenzene (4), vesicant principles of Poison Ivy (Rhus radicans) and other species of Anacardiaceae, are described starting from 1,2-dimethoxybenzene (7).The lithiation of 1,2-dimethoxybenzene (7) has been re-examined and the yield of the product, 2,3-dimethoxyphenyl-lithium (8), re-determined.The reaction of the aryl-lithium with 1,7-dibromoheptane has been studied by g.l.c., using tributyltin chloride as a quenching reagent.The extracts of two plants of the Anacardiaceae family, Semecarpus vitiensis Engl. and Melanorrhoea beccari Engl., have been examined for the presence of urushiols.The bark of the latter has been found to contain gallic acid.
- Halim, Haroen,Locksley, Harry D.,Memon, Janmohammed J.
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p. 2331 - 2337
(2007/10/02)
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