- Tuning the catalytic performance for the semi-hydrogenation of alkynols by selectively poisoning the active sites of Pd catalysts
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Semi-hydrogenation of alkynols to alkenols with Pd-based catalysts is of great significance in fine chemical industries. Industrial Lindlar catalysts, employing Pb to modify the Pd nanoparticles for higher selectivity toward alkenols, however, generally suffer from both a severe activity decrease and environment pollution caused by using heavy metal Pb and additives. Therefore, how to overcome the selectivity-activity paradox remains a great challenge in industry. Here, we report a controllable strategy for the synthesis of semi-hydrogenation catalysts, which successfully improves the catalytic performance through selectively poisoning the edge and corner sites of Pd nanoparticles. When the integrity of the crystal face is reserved, both higher activity (～1340 h-1) and selectivity (～95% at 99% conversion) are achieved in the semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY) in ethanol, an industrially important intermediate product for the synthesis of vitamin E, without adding any toxic additives. What's more, the yield could exceed 98% at 99% conversion under no solvent and organic adsorbate conditions, which had never been achieved before. This work provides a different perspective to design and develop high performance catalysts for semi-hydrogenation of alkenols or even substituted alkynes.
- Mao, Shanjun,Zhao, Bowen,Wang, Zhe,Gong, Yutong,Lü, Guofeng,Ma, Xiao,Yu, Lili,Wang, Yong
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p. 4143 - 4151
(2019/08/07)
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- Stereochemical investigations on the biosynthesis of achiral (Z)-γ-bisabolene in Cryptosporangium arvum
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A newly identified bacterial (Z)-γ-bisabolene synthase was used for investigating the cyclisation mechanism of the sesquiterpene. Since the stereoinformation of both chiral putative intermediates, nerolidyl diphosphate (NPP) and the bisabolyl cation, is lost during formation of the achiral product, the intriguing question of their absolute configurations was addressed by incubating both enantiomers of NPP with the recombinant enzyme, which resolved in an exclusive cyclisation of (R)-NPP, while (S)-NPP that is non-natural to the (Z)-γ-bisabolene synthase was specifically converted into (E)-β-farnesene. A hypothetical enzyme mechanistic model that explains these observations is presented.
- Rinkel, Jan,Dickschat, Jeroen S.
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supporting information
p. 789 - 794
(2019/04/17)
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- Sesquiterpene Cyclizations inside the Hexameric Resorcinarene Capsule: Total Synthesis of δ-Selinene and Mechanistic Studies
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The synthesis of terpene natural products remains a challenging task due to the enormous structural diversity in this class of compounds. Synthetic catalysts are unable to reproduce the tail-to-head terpene cyclization of cyclase enzymes, which create this diversity from just a few simple linear terpene substrates. Recently, supramolecular structures have emerged as promising enzyme mimetics. In the present study, the hexameric resorcinarene capsule was utilized as an artificial cyclase to catalyze the cyclization of sesquiterpenes. With the cyclization reaction as the key step, the first total synthesis of the sesquiterpene natural product δ-selinene was achieved. This represents the first total synthesis of a sesquiterpene natural product that is based on the cyclization of a linear terpene precursor inside a supramolecular catalyst. To elucidate the reaction mechanism, detailed kinetic studies and kinetic isotope measurements were performed. Surprisingly, the obtained kinetic data indicated that a rate-limiting encapsulation step is operational in the cyclization of sesquiterpenes.
- Zhang, Qi,Tiefenbacher, Konrad
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supporting information
p. 12688 - 12695
(2019/08/12)
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- Prenyl Praxis: A Method for Direct Photocatalytic Defluoroprenylation
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The prenyl fragment is the quintessential constituent of terpenoid natural products, a diverse family which contains numerous members with diverse biological properties. In contrast, fluorinated and multifluorinated arenes make up an important class of anthropogenic molecules which are highly relevant to material, agricultural, and pharmaceutical industries. While allylation chemistry is well developed, effective prenylation strategies have been less forthcoming. Herein, we describe the photocatalytic defluoroprenylation, a powerful method that provides access to "hybrid molecules" that possess both the functionality of a prenyl group and fluorinated arenes. This approach involves direct prenyl group transfer under very mild conditions, displays excellent functional group tolerance, and includes relatively short reaction times (4 h), which is the fastest photocatalytic C-F functionalization developed to date. Additionally, the strategy can be extended to include allyl and geranyl (10 carbon fragment) transfers. Another prominent finding is a reagent-dependent switch in regioselectivity of the major product from para to ortho C-F functionalization.
- Priya, Sonal,Weaver, Jimmie D.
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supporting information
p. 16020 - 16025
(2018/11/27)
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- Isotope sensitive branching and kinetic isotope effects to analyse multiproduct terpenoid synthases from Zea mays
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Multiproduct terpene synthases TPS4-B73 and TPS5-Delprim from Zea mays exhibit isotopically sensitive branching in the formation of mono- and sesquiterpene volatiles. The impact of the kinetic isotope effects and the stabilization of the reactive intermediates by hyperconjugation along with the shift of products from alkenes to alcohols are discussed.
- Gatto, Nathalie,Vattekkatte, Abith,K?llner, Tobias,Degenhardt, J?rg,Gershenzon, Jonathan,Boland, Wilhelm
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supporting information
p. 3797 - 3800
(2015/03/30)
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- Biomimetic total synthesis of (-)-neroplofurol and (+)-ekeberin D4triggered by hydrolysis of terminal epoxides
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To accumulate the chemi cal basis of epoxide-opening cascade biogenesis, chemical syntheses of sesqui- and triterpenoids were performed. The biomi metic total syntheses of (-)-neroplofurol (1) and (+)-ekeberin D4(2) were accomplished by protic acid-catalyzed hydrolysis of the terminal epoxide from nerolidol diepoxide 3 and squalene tetraepoxide 4 through single and double 5-exo cyclizations in intermediates 5 and 6, respectively. This chemical reaction mimics the direct hydrolysis mechanism of epoxide hydrol ases, enzymes that catalyze an epoxide-opening reaction to finally produce vicinal diols.
- Kodama, Takeshi,Aoki, Shingo,Matsuo, Tomoki,Tachi, Yoshimitsu,Nishikawa, Keisuke,Morimoto, Yoshiki
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supporting information
p. 1662 - 1664
(2015/02/19)
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- A 1,6-ring closure mechanism for (+)-δ-cadinene synthase?
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Recombinant (+)-δ-cadinene synthase (DCS) from Gossypium arboreum catalyzes the metal-dependent cyclization of (E,E)-farnesyl diphosphate (FDP) to the cadinane sesquiterpene δ-cadinene, the parent hydrocarbon of cotton phytoalexins such as gossypol. In contrast to some other sesquiterpene cyclases, DCS carries out this transformation with >98% fidelity but, as a consequence, leaves no mechanistic traces of its mode of action. The formation of (+)-δ-cadinene has been shown to occur via the enzyme-bound intermediate (3R)-nerolidyl diphosphate (NDP), which in turn has been postulated to be converted to cis-germacradienyl cation after a 1,10-cyclization. A subsequent 1,3-hydride shift would then relocate the carbocation within the transient macrocycle to expedite a second cyclization that yields the cadinenyl cation with the correct cis stereochemistry found in (+)-δ-cadinene. An elegant 1,10-mechanistic pathway that avoids the formation of (3R)-NDP has also been suggested. In this alternative scenario, the final cadinenyl cation is proposed to be formed through the intermediacy of trans, trans-germacradienyl cation and germacrene D. In addition, an alternative 1,6-ring closure mechanism via the bisabolyl cation has previously been envisioned. We report here a detailed investigation of the catalytic mechanism of DCS using a variety of mechanistic probes including, among others, deuterated and fluorinated FDPs. Farnesyl diphosphate analogues with fluorine at C2 and C10 acted as inhibitors of DCS, but intriguingly, after prolonged overnight incubations, they yielded 2F-germacrene(s) and a 10F-humulene, respectively. The observed 1,10-, and to a lesser extent, 1,11-cyclization activity of DCS with these fluorinated substrates is consistent with the postulated macrocyclization mechanism(s) en route to (+)-δ-cadinene. On the other hand, mechanistic results from incubations of DCS with 6F-FPP, (2Z,6E)-FDP, neryl diphosphate, 6,7-dihydro-FDP, and NDP seem to be in better agreement with the potential involvement of the alternative biosynthetic 1,6-ring closure pathway. In particular, the strong inhibition of DCS by 6F-FDP, coupled to the exclusive bisabolyl- and terpinyl-derived product profiles observed for the DCS-catalyzed turnover of (2Z,6E)-farnesyl and neryl diphosphates, suggested the intermediacy of α-bisabolyl cation. DCS incubations with enantiomerically pure [1- 2H1](1R)-FDP revealed that the putative bisabolyl-derived 1,6-pathway proceeds through (3R)-nerolidyl diphosphate (NDP), is consistent with previous deuterium-labeling studies, and accounts for the cis stereochemistry characteristic of cadinenyl-derived sesquiterpenes. While the results reported here do not unambiguously rule in favor of 1,6- or 1,10-cyclization, they demonstrate the mechanistic versatility inherent to DCS and highlight the possible existence of multiple mechanistic pathways.
- Faraldos, Juan A.,Miller, David J.,Gonzalez, Veronica,Yoosuf-Aly, Zulfa,Cascon, Oscar,Li, Amang,Allemann, Rudolf K.
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supporting information; experimental part
p. 5900 - 5908
(2012/05/07)
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- Structural elucidation of cisoid and transoid cyclization pathways of a sesquiterpene synthase using 2-fluorofarnesyl diphosphates
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Sesquiterpene skeletal complexity in nature originates from the enzyme-catalyzed ionization of (trans,trans)-farnesyl diphosphate (FPP) (1a) and subsequent cyclization along either 2,3-transoid or 2,3-cisoid farnesyl cation pathways. Tobacco 5-epi-aristolochene synthase (TEAS), a transoid synthase, produces cisoid products as a component of its minor product spectrum. To investigate the cryptic cisoid cyclization pathway in TEAS, we employed (cis,trans)-FPP (1b) as an alternative substrate. Strikingly, TEAS was catalytically robust in the enzymatic conversion of (cis,trans)-FPP (1b) to exclusively (?99.5%) cisoid products. Further, crystallographic characterization of wild-type TEAS and a catalytically promiscuous mutant (M4 TEAS) with 2-fluoro analogues of both all-trans FPP (1a) and (cis,trans)-FPP (1b) revealed binding modes consistent with preorganization of the farnesyl chain. These results provide a structural glimpse into both cisoid and transoid cyclization pathways efficiently templated by a single enzyme active site, consistent with the recently elucidated stereochemistry of the cisoid products. Further, computational studies using density functional theory calculations reveal concerted, highly asynchronous cyclization pathways leading to the major cisoid cyclization products. The implications of these discoveries for expanded sesquiterpene diversity in nature are discussed.
- Noel, Joseph P.,Dellas, Nikki,Faraldos, Juan A.,Zhao, Marylin,Hess, B. Andes,Smentek, Lidia,Coates, Robert M.,O'Maille, Paul E.
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body text
p. 377 - 392
(2011/02/23)
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- Bisabolyl-derived sesquiterpenes from tobacco 5-epi-aristolochene synthase-catalyzed cyclization of (2Z,6E)-farnesvl diohosohate
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We report the structures and stereochemistry of seven bisabolyl-derived sesquiterpenes arising from an unprecedented 1,6-cyclization (cisoid pathway) efficiently catalyzed by tobacco 5-epi-aristolochene synthase (TEAS). The use of (2Z,6E)-farnesyl diphosphate as an alternate substrate for recombinant TEAS resulted in a robust enzymatic cyclization to an array of products derived exclusively (≥99.5%) from the cisoid pathway, whereas these same products account for ca. 2.5% of the total hydrocarbons obtained using (2E,6E)-farnesyl diphosphate. Chromatographic fractionations of extracts from preparative incubations with the 2Z,6E substrate afforded, in addition to the acyclic allylic alcohols (2Z,6E)-farnesol (6.7%) and nerolidol (3.6%), five cyclic sesquiterpene hydrocarbons and two cyclic sesquiterpene alcohols: (+)-2-epiprezizaene (44%), (-)-α-cedrene (21.5%), (R)-(-)-β-curcumene (15.5%), R-acoradiene (3.9%), 4-epi-α-acoradiene (1.3%), and equal amounts of α-bisabolol (1.8%) and epi-R-bisalolol (1.8%). The structures, stereochemistry, and enantiopurities were established by comprehensive spectroscopic analyses, optical rotations, chemical correlations with known sesquiterpenes, comparisons with literature data, and GC analyses. The major product, (+)-2-epi-prezizaene, is structurally related to the naturally occurring tricyclic alcohol, jinkohol (2-epi-prezizaan-7 β-ol). Cisoid cyclization pathways are proposed by which all five sesquiterpene hydrocarbons are derived from a common (7R)-β-bisabolyl+/pyrophosphate - ion pair intermediate. The implications of the cisoid catalytic activity of TEAS are discussed.
- Faraldos, Juan A.,O'Maille, Paul E.,Dellas, Nikki,Noel, Joseph P.,Coates, Robert M.
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experimental part
p. 4281 - 4289
(2010/05/15)
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- Biosynthesis of the sesquiterpene botrydial in Botrytis cinerea. Mechanism and stereochemistry of the enzymatic formation of presilphiperfolan-8β-ol
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(Figure Presented) Presilphiperfolan-8β-ol synthase, encoded by theBcBOT2 gene from the necrotrophic plant pathogen Botrytis cinerea, cata lyzes the multistep cyclization of farnesyl diphosphate (2) to the tricyclic sesquiterpene alcohol presilphiperfolan-8β-ol (3), the preursor of the phytotoxin botrydial, a strain-dependent fungal virulence factor. Incubation of (1R)-[1-2H]farnesyl diphosphate (2b) with recombinant presilphiperfolan-8β-ol synthase gave exclusively (5R)-[5α-2H]-3b, while complementary incubation of (1S)-[1-2H]FPP (2c) gave (5S)-[5β-2H]-3c. These results establishedthat cyclization of farnesyl diphosphate involves displacement of the d iphosphate group from C-1 with net inversion of configuration and ruled out the proposed intermediacy of the cisoid conformer of nerolidyl diphosphate (9) in the cyclization. While not a mandatory intermediate, (3R)-nerolidyl diphosphate was shown to act as a substrate surrogate. Cyclization of [13,13,13-2H3] farnesyl diphosphate (2d) gave [14,14,14-2H3]-3d, thereby establishing that electrophilic attack takes place exclusively on the si face of the 12,13-double bond of 2. The combined results provide a detailed picture of theconformation of enzyme-bound farnesyl diphosphate at the active site of presilphiperfolan-8β-ol synthase.
- Wang, Chieh-Mei,Hopson, Russell,Lin, Xin,Cane, David E.
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supporting information; experimental part
p. 8360 - 8361
(2009/10/24)
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- Preparation of higher alpha, beta-unsaturated alcohols
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Higher α,β-unsaturated alcohols are prepared by monoethynylation of a ketone by the NH3/KOH method, if desired hydrogenation of the acetylene alcohol in the presence of hydrogen over a Pd-containing thin layer catalyst, purifying distillation of the hydrogenation product, preferably in a dividing wall column with recirculation of the unreacted ketone to the ethynylation step, and, if desired, preparation of higher alcohols having in each case 5 more carbon atoms in the chain by reacting the alcohols prepared by monoethynylation and, if desired, partial hydrogenation with alkyl acetoacetatesor diketene in a Carroll reaction to form ketones and using these as starting materials for the steps ethynylation, optional hydrogenation and fractional distillation.
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- Zeolite Assisted Dehydration of Terpenic Alcohols : Convenient Synthesis of 1,3-Dienes and Oxepane
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Terpenic alcohols undergo facile dehydration over H-ZSM-5 to yield 1,3-dienes, such as farnesenes, ocimene, myrcene and isoprene. Studies on homoallylic alcohol (1e) gave oxepane (2e).
- Reddy, P. Veera,Bhat, Sujata V.
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p. 688 - 689
(2007/10/03)
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- Tellurium in the 'no-solvent' organic synthesis of allylic alcohols
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Elemental tellurium can be reduced by rongalite (HOCH2SO2Na·2H2O)-KOH in the solid phase by application of ultrasound or by microwave irradiation. Without solvent, the organic substrate leg sulfonate ester of an oxiranemethanol) is added with further sonication or irradiation to yield the desired organic product leg allylic alcohols) and elemental Te which may be recycled Phase-transfer conditions (water-toluene) also are satisfactory.
- Xu, Qinyu,Chao, Bin,Wang, Yongmei,Dittmer, Donald C.
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p. 12131 - 12146
(2007/10/03)
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- The synthesis of (3R)-nerolidol
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The sesquiterpene natural product (3R)-nerolidol has been prepared in six steps starting from (3R)linalool.
- Cane, David E.,Ha, Hyun-Joon,McIlwaine, Douglas B.,Pascoe, Keith O.
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p. 7553 - 7554
(2007/10/02)
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- Alkylation du linalol sur les carbones C8 (et C6)
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Metallation of linalool α to the distal double bond with strong bases is described.The corresponding carbanions have been alkylated or oxidized to give mixtures of products resulting from attack at both carbon 8 (major product) and carbon 6 (minor product).
- Cuvigny, Therese,Julia, Marc,Rolando, Christian
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- A Sesquiterpene Glycoside, Loquatifolin A, from the Leaves of Eriobotrya japonica
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The structure of a new sesquiterpene glycoside, loquatifolin A (1), isolated from the leaves of Eriobotrya japonica (Thunb.) Lindle., was established to be α-L-rhamnopyranosyl(1->4)-α-L-rhamnopyranosyl(1->2)-6)>-β-D-glucopyranosyl-6,7-trans-neloridol on the basis of chemical and spectral studies.Keywords - Eriobotrya japonica; Rosaceae; sesquiterpene glycoside; 6,7-trans-nerolidol; 13C-NMR
- Yanagisawa, Hiroaki,Ohshima, Yukio,Okada, Yoshihito,Takahashi, Kunio,Shibata, Shoji
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p. 1270 - 1274
(2007/10/02)
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- A Stereospecific Synthesis of (Z)-δ-Halo-γ,δ-unsaturated Ketones via Haloboration Reaction of Terminal Alkynes
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Michael-type reactions of (Z)-β-bromo- and iodoalkenyl-9-borabicyclononanes (5), readily available by haloboration of 1-alkynes, with acyclic α,β-unsaturated ketones (2) in a nonpolar solvent under Lewis acidic conditions are presented.The products, (Z)-δ-halo-γ,δ-unsaturated ketones (6), are obtained in stereochemically pure form (>98 percent).Since the haloalkenylboranes (5) are prepared in situ from haloboranes (4) and 1-alkynes, the present reaction provides a stereospecific, one-pot, and general synthesis of the title compounds (6).When methyl vinyl ketone (MVK) is used as the Michael acceptor, aldol condensation of the intermediate boron enolate with an excess of MVK occurs.However, the aldol (7) is transformed into the parent haloenone (6') without difficulty upon subsequent, in situ treatment with a base.The same product (6') is prepared directly by the reaction with 3-(trimethylsilyl)-3-buten-2-one.Synthetic utility of the present method is demonstrated by selective syntheses of several natural products.Sulcatol (11) is obtained in an overall yield of 63 percent starting from propyne.In a similar manner, trans-geranyl acetone (14) and trans-nerolidol (15) are prepared stereospecifically (>98 percent) in 62 and 72 percent yields, respectively, from 6-methyl-5-hepten-1-yne (12).
- Satoh, Yoshitaka,Serizawa, Hirokazu,Hara, Shoji,Suzuki, Akira
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p. 5225 - 5228
(2007/10/02)
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- PREPARATION DE CETONES ET D'ALCOOLS INSATURES A PARTIR DE LA METHYLVINYLCETONE. UNE SYNTHESE SIMPLE ET EFFICACE D'ALCOOLS ISOPRENIQUES
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The preparation of olefinic ketones and alcohols by means of a retro Diels-Alder reaction is described.This process has been applied to high yield syntheses of linalool 6e, nerolidol 6f and the sesquiterpene alcohol 10 recently isolated from the alga Laurencia nidifica.
- Bloch, R.
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p. 639 - 644
(2007/10/02)
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- (10R, 11R)-(+)-SQUALENE-10, 11-EPOXIDE: ISOLATION FROM LAURENCIA OKAMURAI AND THE ASYMMETRIC SYNTHESIS
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From a red alga Laurencia okamurai, (10R, 11R)-(+)-squalene-10, 11-epoxide 1 was isolated and its asymmetric synthesis has been achieved starting from trans, trans-farnesol.
- Kigoshi, Hideo,Ojika, Makoto,Shizuri, Yoshikazu,Niwa, Haruki,Yamada, Kiyoyuki
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p. 5413 - 5414
(2007/10/02)
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- Sur la stereochimie de la cyclisation du nerolidol an α-bisabolol
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The cyclisation of linalyl to α-terpinyl derivatives is known to take place with efficient transfer of chirality.Information was needed about the analogous cyclisation of nerolidyl to bisabolyl derivatives.This was made possible through the recent determination of the absolute configuration of bisabolol and epibisabolol.Hydrolysis of (+)(S) nerolidyl paranitrobenzoate has been carried out under the experimental conditons used for (-)(R) linalyl paranitrobenzoate.Strong asymmetric induction was observed about C4 (in the ring) but very little, if any, about C8 (in the chain).The cyclisation of (+)(S) nerolidol has been brought about by 90/10 aqueous formic acid.Under these experimental conditions very little asymmetric induction is observed about C8 or C4.This is explained by rapid racemisation of the starting material under the cyclisation conditions.
- Fourneron, Jean-Dominique,Julia, Marc
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p. 387 - 392
(2007/10/02)
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- Inclusion complex compound, process for its production, and method for its use
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An inclusion complex compound comprising (a) meta-cyclophane and (b) a trans-terpenoid of the formula STR1 wherein n is an integer of 1 to 9; A1 and A2 each represent (1) a hydrogen atom, (2) a halogen atom, (3) an inorganic group containing an oxygen, nitrogen or sulfur atom, (4) an organic group containing 1 to 5 carbon atoms, or (5) an organic group containing an oxygen, nitrogen or sulfur atom and 1 to 5 carbon atoms; and C* is the carbon atom of a carbonyl or methylene group, Included by the meta-cyclophane. This inclusion complex compound can be prepared by contacting the meta-cyclophane with a mixture containing the trans-terpenoid. A trans-terpenoid can be separated from a mixture containing it by utilizing an inclusion complex compound of it with meta-cyclophane.
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