- Energy Read-out as a Probe of Kinetically Hidden Transition States
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The initial energy in a reactive intermediate is derived from the transition state before the intermediate but can affect selectivity after the intermediate. In this way an observable selectivity can report on a prior, kinetically hidden mechanistic step. This new type of mechanistic probe is demonstrated here for the oxidation of 1-methylcyclobutanol by phthaloyl peroxide/Bu4N+Br-, and it supports a hypobromite chain mechanism in place of the previously proposed hydrogen atom transfer mechanism.
- Alvi, Scheherzad,Singleton, Daniel A
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Read Online
- Synthesis of two new enrichable and MS-cleavable cross-linkers to define protein-protein interactions by mass spectrometry
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The cross-linking Mass Spectrometry (XL-MS) technique extracts structural information from protein complexes without requiring highly purified samples, crystallinity, or large amounts of material. However, there are challenges to applying the technique to protein complexes in vitro, and those challenges become more daunting with in vivo experiments. Issues include effective detection and identification of cross-linked peptides from complex mixtures. While MS-cleavable cross-linkers facilitate the sequencing and identification of cross-linked peptides, enrichable cross-linkers increase their detectability by allowing their separation from non-cross-linked peptides prior to MS analysis. Although a number of cross-linkers with single functionality have been developed in recent years, an ideal reagent would incorporate both capabilities for XL-MS studies. Therefore, two new cross-linkers have been designed and prepared that incorporate an azide (azide-A-DSBSO) or alkyne (alkyne-A-DSBSO) to enable affinity purification strategies based on click chemistry. The integration of an acid cleavage site next to the enrichment handle allows easy recovery of cross-linked products during affinity purification. In addition, these sulfoxide containing cross-linking reagents possess robust MS-cleavable bonds to facilitate fast and easy identification of cross-linked peptides using MS analysis. Optimized, gram-scale syntheses of these cross-linkers have been developed and the azide-A-DSBSO cross-linker has been evaluated with peptides and proteins to demonstrate its utility in XL-MS analysis.
- Burke, Anthony M.,Kandur, Wynne,Novitsky, Eric J.,Kaake, Robyn M.,Yu, Clinton,Kao, Athit,Vellucci, Danielle,Huang, Lan,Rychnovsky, Scott D.
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- METALLATION DES CHLOROSILANES PAR LES TRIALKYLSTANNYLANIONS
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The stereochemistry of chlorosilane metallation by stannyl anions of the silacyclopentane series has been studied.Poor stereoselectivity is often observed for this reaction and the expected stannylsilanes are usually contaminated with products of side reactions.Concerning the mechanisms implied in the stannylation reaction, we consider that a reasonable interpretation of the experimental facts is the possibility of two competing processes: nucleophilic SN2 substitution (inversion at Si) and halogen-metal exchange (which implies retention or epimerization at the Si atom).
- Quintard, Jean-Paul,Dumartin, Gilles,Guerin, Christian,Dubac, Jacques,Laporterie, Andre
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Read Online
- Direct conversion of bromohydrins to ketones
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The direct conversion of halohydrins to ketones can be achieved by irradiation in benzene or toluene in the presence of small amounts of p-toluenesulfonic acid. A two step conversion of terminal alkenes to methylketones is thus achieved with good yields and inexpensive reagents.
- Piva
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Read Online
- Palladium/Copper-catalyzed Oxidation of Aliphatic Terminal Alkenes to Aldehydes Assisted by p-Benzoquinone
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The development of an anti-Markovnikov Wacker-type oxidation for simple aliphatic alkenes is a significant challenge. Herein, a variety of aldehydes can be selectively obtained from various unbiased aliphatic terminal alkenes using PdCl2(MeCN)2/CuCl in the presence of p-benzoquinone (BQ) under mild reaction conditions. Isomerization of the terminal alkene to the internal alkene was suppressed via slow addition of the starting material to the reaction mixture. In addition to the Pd catalyst, CuCl and BQ were essential in order to obtain the anti-Markovnikov product with high selectivity. Terminal alkenes bearing a halogen substituent afforded their corresponding aldehydes with high anti-Markovnikov selectivity. The halogen acts as a directing group in the reaction. DFT calculations indicate that a μ-chloro Pd(II)?Cu(I) bimetallic species with BQ coordinated to Cu is the catalytically active species in the case of a terminal alkene without a directing group.
- Komori, Saki,Yamaguchi, Yoshiko,Murakami, Yuka,Kataoka, Yasutaka,Ura, Yasuyuki
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p. 3946 - 3955
(2020/07/06)
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- Radical dehydroxylative alkylation of tertiary alcohols by Ti catalysis
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Deoxygenative radical C?C bond-forming reactions of alcohols are a long-standing challenge in synthetic chemistry, and the current methods rely on multistep procedures. Herein, we report a direct dehydroxylative radical alkylation reaction of tertiary alcohols. This new protocol shows the feasibility of generating tertiary carbon radicals from alcohols and offers an approach for the facile and precise construction of all-carbon quaternary centers. The reaction proceeds with a broad substrate scope of alcohols and activated alkenes. It can tolerate a wide range of electrophilic coupling partners, including allylic carboxylates, aryl and vinyl electrophiles, and primary alkyl chlorides/bromides, making the method complementary to the cross-coupling procedures. The method is highly selective for the alkylation of tertiary alcohols, leaving secondary/primary alcohols (benzyl alcohols included) and phenols intact. The synthetic utility of the method is highlighted by its 10-g-scale reaction and the late-stage modification of complex molecules. A combination of experiments and density functional theory calculations establishes a plausible mechanism implicating a tertiary carbon radical generated via Ti-catalyzed homolysis of the C?OH bond.
- Xie, Hao,Guo, Jiandong,Wang, Yu-Quan,Wang, Ke,Guo, Peng,Su, Pei-Feng,Wang, Xiaotai,Shu, Xing-Zhong
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supporting information
p. 16787 - 16794
(2020/11/09)
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- A Modular and Diastereoselective 5 + 1 Cyclization Approach to N-(Hetero)Aryl Piperidines
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A new general de novo synthesis of pharmaceutically important N-(hetero)aryl piperidines is reported. This protocol uses a robustly diastereoselective reductive amination/aza-Michael reaction sequence to achieve rapid construction of complex polysubstituted ring systems starting from widely available heterocyclic amine nucleophiles and carbonyl electrophiles. Notably, the diastereoselectivity of this process is enhanced by the presence of water, and DFT calculations support a stereochemical model involving a facially selective protonation of a water-coordinated enol intermediate.
- Larsen, Matthew A.,Hennessy, Elisabeth T.,Deem, Madeleine C.,Lam, Yu-Hong,Saurí, Josep,Sather, Aaron C.
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supporting information
p. 726 - 732
(2020/01/31)
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- Palladium-Catalyzed Aerobic Anti-Markovnikov Oxidation of Aliphatic Alkenes to Terminal Acetals
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Terminal acetals were selectively synthesized from various unbiased aliphatic terminal alkenes and 1,2-, 1,3-, or 1,4-diols using a PdCl2(MeCN)2/CuCl catalyst system in the presence of p-toluquinone under 1 atm of O2 and mild reaction conditions. The slow addition of terminal alkenes suppressed the isomerization to internal alkenes successfully. Electron-deficient cyclic alkenes, such as p-toluquinone, were key additives to enhance the catalytic activity and the anti-Markovnikov selectivity. The halogen groups in the alkenes were found to operate as directing groups, suppressing isomerization and increasing the selectivity efficiently.
- Komori, Saki,Yamaguchi, Yoshiko,Kataoka, Yasutaka,Ura, Yasuyuki
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p. 3093 - 3099
(2019/03/29)
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- Asymmetric Reductive Carbocyclization Using Engineered Ene Reductases
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Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in α,β-unsaturated compounds bearing an electron-withdrawing group, for example, a carbonyl group. This asymmetric reduction has been exploited for biocatalysis. Going beyond its canonical function, we show that members of this enzyme family can also catalyze the formation of C?C bonds. α,β-Unsaturated aldehydes and ketones containing an additional electrophilic group undergo reductive cyclization. Mechanistically, the two-electron-reduced enzyme cofactor FMN delivers a hydride to generate an enolate intermediate, which reacts with the internal electrophile. Single-site replacement of a crucial Tyr residue with a non-protic Phe or Trp favored the cyclization over the natural reduction reaction. The new transformation enabled the enantioselective synthesis of chiral cyclopropanes in up to >99 % ee.
- Heckenbichler, Kathrin,Schweiger, Anna,Brandner, Lea Alexandra,Binter, Alexandra,Toplak, Marina,Macheroux, Peter,Gruber, Karl,Breinbauer, Rolf
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supporting information
p. 7240 - 7244
(2018/06/15)
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- Hydrogen Borrowing Catalysis with Secondary Alcohols: A New Route for the Generation of β-Branched Carbonyl Compounds
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A hydrogen borrowing reaction employing secondary alcohols and Ph? (Me5C6) ketones to give β-branched carbonyl products is described (21 examples). This new C-C bond forming process requires low loadings of [Cp?IrCl2]2, relatively low temperatures, and up to 2.0 equiv of the secondary alcohol. Substrate-induced diastereoselectivity was observed, and this represents the first example of a diastereoselective enolate hydrogen borrowing alkylation. By utilizing the Ph? group, the β-branched products could be straightforwardly cleaved to the corresponding esters or amides using a retro-Friedel-Crafts reaction. Finally, this protocol was applied to the synthesis of fragrance compound (±)-3-methyl-5-phenylpentanol.
- Akhtar, Wasim M.,Cheong, Choon Boon,Frost, James R.,Christensen, Kirsten E.,Stevenson, Neil G.,Donohoe, Timothy J.
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supporting information
p. 2577 - 2580
(2017/03/01)
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- Regioselective Ylide Formation on Acetal-Functionalized Trialkyl Phosphonium Salts: Extending the Scope of Carbonyl Homologation
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The discovery of a complex-induced proximity effect and scope of regioselective ylide formation on acetal- and ketal-functionalized trialkylphosphine-derived phosphonium salts is explored as a route to homologated unsaturated carbonyl derivatives.
- Narayanappa, Arkesh,Hurem, David,McNulty, James
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supporting information
p. 2961 - 2965
(2017/10/06)
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- A simple microwave-assisted preparation of 2-bromo-1-alkenes from 1-alkynes using the LiBr-TMSCl-TEAB reagent system
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2-Bromo-1-alkenes are cleanly and conveniently generated in good yields and selectivities via microwave-assisted hydrobromination of 1-alkynes using a combination of lithium bromide (LiBr), chlorotrimethylsilane (TMSCl), and tetraethylammonium bromide (TEAB) in acetonitrile (MeCN).
- Bunrit, Anon,Ruchirawat, Somsak,Thongsornkleeb, Charnsak
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supporting information; experimental part
p. 3124 - 3127
(2011/06/26)
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- Probing the active site of rat porphobilinogen synthase using newly developed inhibitors
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The structurally related tetrapyrrolic pigments are a group of natural products that participate in many of the fundamental biosynthetic and catabolic processes of living organisms. Porphobilinogen synthase catalyzes a rate-limiting step for the biosyntheses of tetrapyrrolic natural products. In the present study, a variety of new substrate analogs and reaction intermediate analogs were synthesized, which were used as probes for studying the active site of rat porphobilinogen synthase. The compounds 1, 3, 6, 9, 14, 16, and 28 were found to be competitive inhibitors of rat porphobilinogen synthase with inhibition constants ranging from 0.96 to 73.04 mM. Compounds 7, 10, 12, 13, 15, 17, 18, and 26 were found to be irreversible enzyme inhibitors. For irreversible inhibitors, loose-binding inhibitors were found to give stronger inactivation. The amino group and carboxyl group of the analogs were found to be important for their binding to the enzyme. This study increased our understanding of the active site of porphobilinogen synthase.
- Li, Nan,Chu, Xiusheng,Liu, Xiaojun,Li, Ding
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scheme or table
p. 33 - 40
(2009/05/30)
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- 6- and 14-Fluoro farnesyl diphosphate: Mechanistic probes for the reaction catalysed by aristolochene synthase
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The catalytic mechanism of the enzyme aristolochene synthase from Penicillium roqueforti (PR-AS) has been probed with the farnesyl diphosphate analogues 6- and 14-fluoro farnesyl diphosphate (1b and 1c). Incubation of these analogues with PR-AS followed by analysis of the reaction products by GC-MS and NMR spectroscopy indicated that these synthetic FPP analogues were converted to the fluorinated germacrene A analogues 3b and 3c, respectively. In both cases the position of the fluorine atom prevented the formation of the eudesmane cation analogues 4b and 4c. These results highlight that germacrene A is an on-path reaction intermediate during PR-AS catalysis and shed light on the mechanism by which germacrene A is converted to eudesmane cation. They support the proposal that the role of PR-AS in the cyclisation is essentially passive in that it harnesses the inherent chemical reactivity present in the substrate by promoting the initial ionisation of farnesyl diphosphate and by acting as a productive template to steer the reaction through an effective series of cyclisations and rearrangements to (+)-aristolochene (7a).
- Miller, David J.,Yu, Fanglei,Knight, David W.,Allemann, Rudolf K.
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experimental part
p. 962 - 975
(2009/05/30)
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- Ionic liquid, surrogate hydrogen bromide reagent for ring opening of cyclopropyl ketones
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(Chemical Equation Presented) Ionic liquid reagents created by addition of 1 equiv of either CF3CO2H or CF3SO3H to N-pentylpyridinium bromide exhibit excellent chemical reactivities as surrogate HBr reagents in ring-opening reactions of cyclopropyl ketones as well as of 2,2-difluorocyclopropyl ketones to form the respective 3-bromopropyl or 3-bromo-2,2-difluoropropyl ketones in good to excellent yields.
- Xu, Wei,Dolbier Jr., William R.,Salazar, Jose
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p. 3535 - 3538
(2008/09/20)
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- Probing the reaction mechanism of aristolochene synthase with 12,13-difluorofarnesyl diphosphate
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12,13-Difluorofarnesyl diphosphate, prepared using Suzuki-Miyaura chemistry, is a potent inhibitor of aristolochene synthase (AS), indicating that the initial cyclisation during AS catalysis generates germacryl cation in a concerted reaction. The Royal Society of Chemistry.
- Yu, Fanglei,Miller, David J.,Allemann, Rudolf K.
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p. 4155 - 4157
(2008/09/16)
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- Convenient synthesis of ε-halo-β-ketoesters and γ,γ′-dibromoalkanones by regio- and chemoselective reaction of 2-alkylidenetetrahydrofurans with boron trihalides: A "ring-closure/ring- cleavage" strategy
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The reaction of boron tribromide and boron trichloride with 2-alkylidenetetrahydrofurans, readily available on the basis of cyclizations of free and masked dianions with 1,2-dielectrophiles, allowed an efficient synthesis of a variety of carbonyl compounds with remote halide functionality. This includes the chemo- and regioselective synthesis of 6-bromo- and 6-chloro-3-oxoalkanoates and 1,7-dibromoheptan-4-ones. The approach outlined herein can be regarded as a "ring-closure/ring-cleavage" strategy.
- Bellur, Esen,Langer, Peter
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p. 3819 - 3825
(2007/10/03)
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- An unexpected product in the photooxygenation of a cyclic enol ether
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The photooxygenation product of a cyclic enol ether conjugated with an o-phenylene ring is a novel epoxy compound instead of a 1,2,4-trioxane analogue. The structure of the compound was elucidated by X-ray analysis.
- Wu, Jin-Ming,Li, Ying
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p. 6737 - 6739
(2007/10/03)
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- alpha 1a adrenergic receptor antagonists
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This invention relates to novel compounds, their synthesis and use as selective alpha 1a adrenergic receptor antagonists. One application of the compounds is in the treatment of benign prostatic hyperplasia. The compounds are selective in their ability to relax smooth muscle tissue enriched in the alpha 1a receptor subtype without at the same time inducing hypotension. One such tissue is found surrounding the urethral lining. Therefore, one utility of the instant compounds is to provide acute relief to males suffering from benign prostatic hyperplasia, by permitting less hindered urine flow. Another utility of the instant compounds is provided by combination with a human 5-alpha reductase inhibitory compound, such that both acute and chronic relief from the effects of benign prostatic hyperplasia are achieved.
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- Alpha 1a adrenergic receptor antagonists
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This invention relates to novel compounds, their synthesis and use as selective α 1a adrenergic receptor antagonists. One application of the compounds is in the treatment of benign prostatic hyperplasia. The compounds are selective in their ability to relax smooth muscle tissue enriched in the α 1a receptor subtype without at the same time inducing hypotension. One such tissue is found surrounding the urethral lining. Therefore, one utility of the instant compounds is to provide acute relief to males suffering from benign prostatic hyperplasia, by permitting less hindered urine flow. Another utility of the instant compounds is provided by combination with a human 5-alpha reductase inhibitory compound, such that both acute and chronic relief from the effects of benign prostatic hyperplasia are achieved.
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- Oxidation of 1-alkylcycloalkanols with PbIV and MnIII compounds under mechanical activation
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A mechanoactivated solid-state oxidative decyclization of 1-alkylcycloalkanols under the action of the Pb(OAc)4-MX or Mn(OAc)3-MX systems (MX is a metal halide) was carried out for the first time. The reaction affords exclusively ω-haloalkanones.
- Kapustina,Sokova,Makhaev,Petrova,Nikishin
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p. 2080 - 2082
(2007/10/03)
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- Formal synthesis of (Z,Z)-dodeca-3,6-dien-11-olide, pheromone of oryzaephilus surinamensis and oryzaephilus mercator (Coleoptera: Cucujidae)
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Racemic 11-Hydroxy-3(Z),6(Z)-dodecadienoic acid, the nearest precursor of the title lactone, was synthesized from 5-hydroxy-2-pentanone in eight steps with an overall yield of 1.48%. The key stage of the synthesis, regio- and stereoselective construction of the system of two conjugated Z,Z-double bonds, was accomplished by addition of two hydrogen molecules to methyl 11-oxo-2,4-dodecadien-6-ynoate in the presence of η6-(methyl benzoate)tricarbonylchromium. 1998 MAHK Hayka/Interperiodica Publishing.
- Vasil'ev,Serebryakov
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p. 981 - 984
(2007/10/03)
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- Radical addition to carbenoids. Chain reactions of α-diazo carbonyl compounds with triorganotin hydrides, tris(trimethylsilyl)silane and allyltributylstannane
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α-Diazo ketones RC(O)CH=N2 react with tributyltin hydride at 60°C in benzene to give the corresponding α-stannyl ketones RC(O)CH2SnBu3, which exist in equilibrium with the stannyl enol ether tautomers R(Bu3SnO)C=CH2. The reactions are initiated by di-tert-butyl hyponitrite and follow a free-radical chain mechanism. Triphenyltin hydride and tris(trimethylsilyl)silane [(TMS)3SiH] react similarly, the latter to yield the α-silyl ketone RC(O)CH2Si(TMS)3 which does not isomerise to the more stable silyl enol ether R[(TMS)3SiO]C=CH2 under the reaction conditions. This result indicates that TMS3Si. reacts at the α-carbon atom of the α-diazo ketone to give R(CO)CHSiTMS3, probably via an initial diazenyl radical adduct; triorganotin radicals are assumed to react in the same way. When the group R in the α-diazo ketone is but-3-enyl, the intermediate α-metalloalkyl radical undergoes 5-exo-cyclisation. Allyltributylstannane reacts with α-diazo ketones and with ethyl α-diazoacetate in refluxing benzene, in the presence of 2,2′-azo(2-methylpropionitrile) as initiator, to give butenyl ketones RC(O)CH2CH2CH=CH2 and ethyl pent-4-enoate, respectively, after a hydrolytic work-up.
- Dang, Hai-Shan,Roberts, Brian P.
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p. 769 - 775
(2007/10/03)
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- Synthesis of labelled [13C6]testosterone and [13C5]19-nortestosterone
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The condensation of ethyl acetoacetate-13C4 and ethyl bromoacetate-13C2 afforded, in seven steps, (1,2,3,4,5-13C5) 5-(diethylphosphono)-2-pentanone ethylene ketal 9. The reaction of this labelled compound with 7-[[(1,1-dimethylethyl)-dimethylsilyl]oxy]-1,6,6a,7,8, 9, 9a, 9b-octahydro-6a-methyl-[6aS-(6aa,7a,9aβ,9ba)] cyclopenta[f][1]benzopyran-3 (2H)-one 13 gave the benzindenone 14 which was converted to (1,2,3,4,10,19-13C6)testosterone 17 then, into (1,2,3,4,10-13C5)19-nortestosterone 18 by a reductive alkylation method.
- Joubert,Beney,Marsura,Luu-Duc
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p. 745 - 754
(2007/10/02)
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- Control of dispersity and stereochemistry in free radical telomerizations: A radical addition, cyclization, chain transfer (ACT) strategy
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A general strategy for the stereoselective preparation of n = 2 telomers displaying narrow dispersity is reported. Covalent assemblies composed of a rigid base compound, flexible tethers, and oxazolidine acrylamide monomers were reacted under free radical conditions to afford macrocyclic precursors to the targeted telomers through an addition, cyclization, chain transfer (ACT) sequence. Subsequent hydrolysis and esterification afforded the desired products with excellent stereoselectivity and teloselectivity. Systematic variation of system components (the rigid base compound, the functionality linking base compound to the tethers, the length of the tethers, the configuration at the site of oxazolidine attachment, and the auxiliary blocking group) allowed for identification of the structural elements necessary for successful implementation. It was found that each of these variables had a marked influence on the performance of the covalent assembly.
- Porter, Ned A.,Miracle, Gregory S.,Cannizzaro, Scott M.,Carter, Randall L.,McPhail, Andrew T.,Liu, Lin
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p. 10255 - 10266
(2007/10/02)
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- INSECT PHEROMONES AND THEIR ANALOGS. XLVII. SYNTHESIS OF 11-OXODODECA-3,6-DIYNOIC ACID - THE ACYCLIC PRECURSOR OF A MACROLIDE COMPONENT OF PHEROMONES OF Oryzaephilus mercator AND O. surinamensis
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A new approach is proposed to the synthesis of 11-oxododeca-3,6-diynoic acid - the acyclic precursor of a macrolide component of pheromones of Oryzaephilus mercator and O. surinamensis - from the readily available tetrahydropyran or allylacetone via the intermediate 5-bromo-2,2-ethylenedioxypentane.
- Odinokov, V. N.,Ishmuratov, G. Yu.,Kharisova, R. Ya.,Vakhidov, R. R.,Botsman, L. P.,Tolstikov, G. A.
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p. 240 - 244
(2007/10/02)
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- Alkenyl bromides by brominative deoxygenation of ketones in one or two steps
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The conversion of ketones into alkenyl bromides is accomplished in one or two steps by 2,2,2-tribromo-2,2-dihydro-1,3,2-benzodioxaphosphole or by the dibromomethyl methyl ether prepared therefrom. Investigations of the scope and limitations provide some hints for the preparative planning and improvement.
- Von Roman,Ruhdorfer,Knorr
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p. 985 - 992
(2007/10/02)
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- OXIDATION OF 1-METHYLCYCLOBUTANOL BY Pb(IV) AND Mn(III) COMPOUNDS
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The main product of the reaction of 1-methylcyclobutanol with Pb(OAc)4 in benzene is 1-phenyl-4-pentanone; the use of Mn(OAc)3 in acetic acid gives a mixture of 2,9-decanedione and methyl propyl ketone; 1-(chloro-, bromo-, thiocyano-, or ccyano)-4-pentanone is formed in the presence of the systems Pb(OAc)4-metal halide or Mn(OAc)3-metal halide. Keywords: oxidation, 1-methylcyclobutanol, lead tetraacetate, manganese triacetate, β-cleavage.
- Kapustina, N.I.,Nikishin, G.I.
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p. 2189 - 2192
(2007/10/02)
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- Catalyse par le palladium at la lumiere ultra-violette de l'oxydation d'alcenes par l'oxygene moleculaire
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The light-promoted oxidation of terminal alkenes by oxygen in the presence of catalytic amounts of palladium(II) complexes led to corresponding α,β-ethylenic carbonyl compounds and methyl ketones; rapid and extensive isomerisation of the starting alkene is observed.The effect of acetone as solvent on the efficiency of these oxidations is discussed.
- Muzart, Jacques,Pale, Patrick,Pete, Jean-Pierre
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p. 267 - 274
(2007/10/02)
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- Synthesis of Averufin and its Role in Aflatoxin B1 Biosynthesis
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Described are two total syntheses of (+/-)-averufin (4) proceeding through a common intermediate and predicated on the efficient introduction of isotopic label(s) at side-chain and nuclear sites for the purpose of biosynthetic investigations of aflatoxin B1 (8).Using these methods, (+/-)--and --averufin, (65) and (68) respectively, and a 1:1 mixture of (+/-)-- and --averufin (71) were prepared and incorporated into aflatoxin B1 using mycelial suspensions of Aspergillus parasiticus (SU-1).In each instance efficient and specific utilization of label was observed in the product by (13)C-n.m.r.spectroscopy, demonstrating the intact incorporation of averufin.When compared with earlier observations of acetate incorporation, a complete correlation of the carbon skeleton from the intermediate anthraquinone stage of the four carbons lost in this overall process were unambiguously identified.In the formation of the dihydrobisfuran, the anthraquinone nucleus migrates to C-2' to branch the linear side-chain of averufin.Deuterium bound at C-1' in averufin is carried to C-13 of aflatoxin.Preparation from (+/-)-averufin (68) of (+/-)--averufin (73) and incorporation of the latter into versiconal acetate (5) demonstrated loss of the terminal two carbons of the averufin side-chain, presumably as acetate, by way of a Baeyer-Villiger-like oxidation.
- Townsend, Craig A.,Christensen, Siegfried B.,Davis, Steven G.
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p. 839 - 862
(2007/10/02)
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- Synthese et heterocyclisation de β-ceto-esters ω-alleniques
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β-keto-esters 1 and 2, diversely substituted on the allenic system, have been synthesized by a sequence, the key step of which being a Blaise reaction of an allenic nitrile.Submitted to the catalytic action of both a Lewis acid and a Broensted acid, they are converted exclusively to oxygenated heterocyclic compounds.The same behaviour is observed with the keto-esters 3 and with the ketones 4.An explanation is given for the absence of carbocyclization previously observed with certain ethylenic and acetylenic homologs of 1, 2 or 3.
- Delair, Thierry,Doutheau, Alain,Gore, Jacques
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p. 125 - 131
(2007/10/02)
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- SYNTHESIS OF (+/-)-ZEARALENONE
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The aliphatic portion of (+/-)-zearalenone has been synthesised by a new simple route starting from 2,3-dihydropyran and 2-acetyl-γ-butyrolactone by employing dithiane for C-C bond formation.The final condensation of this segment with the aromatic part and subsequent transformations led to (+/-)-zearalenone.
- Rama Rao, A. V.,Deshmukh, M. N.,Sharma, G. V. M.
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p. 779 - 784
(2007/10/02)
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- SYNTHESIS OF SINGLE ISOMERS (E OR Z) OF PROTECTED γ,δ-UNSATURATED KETONES BY THE HORNER-WITTIG REACTION
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The lithium derivative of the γ-diphenylphosphinoyl ketal (10a) added to aldehydes and ketones to give stable Horner-Wittig intermediates (11) which were separated and converted into single isomers (E or Z) or γ,δ-unsaturated ketals (12). erythro-Adducts (11) and hence Z-(12), were selectively formed by addition of aldehydes and threo adducts (11), and hence E-(12), by reduction of the corresponding α-diphenylphosphinoyl ketones (13), prepared by acylation of the same γ-diphenylphosphinoyl ketal (10a).
- Cornish Christopher A.,Warren, Stuart
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p. 2585 - 2598
(2007/10/02)
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- A FACILE METHOD FOR THE CONVERSION OF PRIMARY ALKYL CHLORIDES TO THE CORRESPONDING BROMIDES
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Treatment of several representative primary alkyl chlorides with one equivalent of sodium bromide in 2:1 (v/v) N,N-dimethylformamide : dibromoethane at 100 deg C for several hours resulted in their quantitative conversion to the corresponding bromides.
- Babler, James H.,Spina, Kenneth P.
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p. 1313 - 1320
(2007/10/02)
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- Cyclisation des alcools δ-alleniques par le nitrate d'argent ou les sels mercuriques. Synthese d'α-alcenyl-2 tetrahydropyrannes
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Eight diversely substituted δ-allenic alcohols have been synthesized by using three different methods for the formation of the allenic linkage.When treated with silver nitrate or mercuric salts, these alcohols are transformed in fairly good yields into α-alkenyl-2 tetrahydropyrans.In addition to its regioselectivity in the formation of the heterocycle this reaction shows in certain cases a high stereoselectivity.Alcohols monosubstituted on the thermal allenic carbon lead to more than 90percent of the E product whereas the 2,4 or 2,6 disubstituted tetrahydropyrans are obtained in predominantly the Z configuration.
- Audin, Patrick,Doutheau, Alain,Gore, Jacques
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p. 297 - 306
(2007/10/02)
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- STEREO-CONTROLLED SYNTHESIS OF γ,δ-UNSATURATED KETONES BY THE HORNER-WITTIG REACTION
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E and Z isomers of γ,δ-unsaturated ketals may separately be prepared by the Horner-Wittig reaction between 5-diphenyl-phosphinoylpentan-2-one ethylene acetal (6) and aldehydes, esters, or ketones.
- Cornish, Christopher A.,Warren, Stuart
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p. 2603 - 2606
(2007/10/02)
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- SYNTHESIS OF SUBSTITUTED METHYLENECYCLOPROPANES BY METALLATION OF CYCLOPROPYL BROMIDES CONTAINING A METHYLENECYCLOPROPANE FRAGMENT
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In the reaction of 1-cyclopropyl-1-(1-bromocyclopropyl)methylenecyclopropane and 1-methyl-1-(1-bromocyclopropyl)methylenecyclopropane with butyllithium or magnesium in tetrahydrofuran the organometallic derivatives of cyclopropyl-substituted methylenecyclopropanes with the metal atom in the cyclopropane fragment are formed.The reaction of the obtained organometallic compounds with electrophilic agents can be used to introduce deuterium, the trimethylsilyl group, and other substituents into the cyclopropane fragment.The metallation of the above-mentioned bromides with methyllithium is not suitable for the synthesis of organometallic compo unds, since the alkylation products are formed quantitatively.When treated with magnesium in tetrahydrofuran with subsequent decomposition with water, 1,1-di(1-bromocyclopropyl)-methylenecyclopropane gives a mixture of 4-cyclopropylidenedispiroheptane and 1,1-dicyclopropylmethylenecyclopropane, the composition of which depends on the reaction conditions.
- Donskaya, N. A.,Akhachinskaya, T. V.,Leonova, T. V.,Shulishov, E. V.,Shabarov, Yu. S.
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p. 487 - 493
(2007/10/02)
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