- Exploring the substrate specificity of Cytochrome P450cin
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Cytochromes P450 are enzymes that catalyse the oxidation of a wide variety of compounds that range from small volatile compounds, such as monoterpenes to larger compounds like steroids. These enzymes can be modified to selectively oxidise substrates of interest, thereby making them attractive for applications in the biotechnology industry. In this study, we screened a small library of terpenes and terpenoid compounds against P450cin and two P450cin mutants, N242A and N242T, that have previously been shown to affect selectivity. Initial screening indicated that P450cin could catalyse the oxidation of most of the monoterpenes tested; however, sesquiterpenes were not substrates for this enzyme or the N242A mutant. Additionally, both P450cin mutants were found to be able to oxidise other bicyclic monoterpenes. For example, the oxidation of (R)- and (S)-camphor by N242T favoured the production of 5-endo-hydroxycamphor (65–77% of the total products, dependent on the enantiomer), which was similar to that previously observed for (R)-camphor with N242A (73%). Selectivity was also observed for both (R)- and (S)-limonene where N242A predominantly produced the cis-limonene 1,2-epoxide (80% of the products following (R)-limonene oxidation) as compared to P450cin (23% of the total products with (R)-limonene). Of the three enzymes screened, only P450cin was observed to catalyse the oxidation of the aromatic terpene p-cymene. All six possible hydroxylation products were generated from an in vivo expression system catalysing the oxidation of p-cymene and were assigned based on 1H NMR and GC-MS fragmentation patterns. Overall, these results have provided the foundation for pursuing new P450cin mutants that can selectively oxidise various monoterpenes for biocatalytic applications.
- Stok, Jeanette E.,Giang, Peter D.,Wong, Siew Hoon,De Voss, James J.
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- In vivo and in vitro hydroxylation of cineole and camphor by cytochromes P450CYP101A1, CYP101B1 and N242A CYP176A1
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Cytochromes P450 (P450s) are valuable enzymes that can generate a range of useful compounds via biocatalytic oxidations that complement traditional synthetic chemistry. In this study three bacterial P450s, P450cam (CYP101A1), CYP101B1 and the m
- Stok, Jeanette E.,Hall, Emma A.,Stone, Isobella S.J.,Noble, Margaret C.,Wong, Siew Hoon,Bell, Stephen G.,De Voss, James J.
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- General and efficient α-oxygenation of carbonyl compounds by TEMPO induced by single-electron-transfer oxidation of their enolates
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A generally applicable method for the synthesis of protected α-oxygenated carbonyl compounds is reported. It is based on the single-electron-transfer oxidation of easily generated enolates to the corresponding α-carbonyl radicals. Coupling with the stable free radical TEMPO provides α-(piperidinyloxy) ketones, esters, amides, acids or nitriles in moderate-to-excellent yields. Enolate aggregates influence the outcome of the oxygenation reactions significantly. Competitive reactions have been analyzed and conditions for their minimization are presented. Chemoselective reduction of the products led to either N-O bond cleavage to α-hydroxy carbonyl compounds or reduction of the carbonyl functionality tomonoprotected 1,2-diols or O-protected amino alcohols. The oxygenation of enolates proves to be the most general and effective methodology for the synthesis of O-protected α-oxy carbonyl compounds and nitriles A. The scope and limitations of the electron-transfer-induced radical coupling reaction with TEMPO are presented. The reaction pathways are outlined. Methods for the deprotection to α-hydroxy carbonyl compounds B are provided and discussed. Copyright
- Dinca, Emanuela,Hartmann, Philip,Smrcek, Jakub,Dix, Ina,Jones, Peter G.,Jahn, Ullrich
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supporting information
p. 4461 - 4482
(2012/10/30)
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- Reduction of various ketones by red algae
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The reduction of acetophenone derivatives, (+)- and (-)-camphorquinones and steroidal ketones using red algae (Cyanidioschyzon merolae 10D and Cyanidium caldarium) was investigated. It was found that fluoro, chloro and bromo acetophenone derivatives 1a-i were reduced with good enantioselectivity. On the contrary, reduction of methyl and methoxy acetophenone 1j-o showed low enantioselectivity. The reduction followed Prelog's rule, giving the (S)-alcohols in all cases. Moreover, (+)- camphorquinone 5a was reduced to give (-)-3S- exo-hydroxycamphor 5d as the major product with high stereoselectivity in high yield. In addition, it was found that reduction of 5α-androstane-3,17-dione 8a gave the 3α-OH isomer (3α-OH/3β-OH = 76/24) with high stereoselectivity. Overall it was found that C. merolae and C. caldarium were able to reduce various substrates.
- Utsukihara, Takamitsu,Misumi, Osami,Kato, Nakahide,Kuroiwa, Tsuneyoshi,Horiuchi, C. Akira
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p. 1179 - 1185
(2007/10/03)
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- A novel synthesis of α-hydroxy- and α,α′- dihydroxyketone from α-iodo and α,α′-diiodo ketone using photoirradiation
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A novel reaction of α-iodo ketone (α-iodocycloalkanone, α-iodo-β-alkoxy ester, and α-iodoacyclicketone) with irradiation under a high-pressure mercury lamp gave the corresponding α-hydroxyketone in good yields. In the case of α,α′- diiodo ketone, α,α′-dihydroxyketone which little has been reported until now was obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxy- and α,α′- dihydroxyketone.
- Horiuchi, C. Akira,Takeda, Akinori,Chai, Wen,Ohwada, Kishoh,Ji, Shun-Jun,Takahashi, T. Tomoyoshi
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p. 9307 - 9311
(2007/10/03)
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- Biotransformation of (+)- and (-)-camphorquinones by plant cultured cells
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Biotransformation of (+)- and (-)-camphorquinones with suspension plant cultured cells of Nicotiana tabacum and Catharanthus roseus was investigated. It was found that the plant cultured cells of N. tabacum and C. roseus reduce stereoselectively the carbonyl group of (+)- and (-)-camphorquinones to the corresponding α-keto alcohols.
- Chai, Wen,Hamada, Hiroki,Suhara, Jumpei,Akira Horiuchi
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p. 669 - 673
(2007/10/03)
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- Diastereoselective Hydroxylation of Titanium Enolates with tert-Butylhydroperoxide
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The oxidation of titanium enolates with tert-butylhydroperoxide has been investigated and the main reaction products, the corresponding α-hydroxyketones 7a-f, isolated.The highest diastereoselectivities (>95percent de) were obtained, when titanium enolates of camphor 2d-6d were employed.For comparison, the oxidation of the enolates with dimethyldioxirane is discussed.
- Schulz M.,Kluge, R.,Schuessler, M.,Hoffmann, G.
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p. 3175 - 3180
(2007/10/02)
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- Dimethyldioxirane Oxidation of Titanium Enolates: Diastereoselective α-Hydroxylations
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The oxidation of titanium enolates, derived from a transmetalation of the corresponding lithium enolates with (i-PrO)3TiCl, (Et2N)3TiCl, or Cp2TiCl2, by dimethyldioxirane has been investigated.Furthermore, the diastereoselective hydroxylation of the chiral metal enolates, e.g., derived from camphor (1f), menthone (1g), flavanone (1h), and 2-benzylcyclopentanone (1i), by dimethyldioxirane has been examined.The diastereoselectivity of the oxygen transfer strongly depends on the metal partner coordinated to the enolate.The titanium enolates 4 resulted in much higher diastereoselectivities (up to 96percent de) than the corresponding sodium enolates 5 and at least as high if not higher than the silyl enol ethers 6.Moreover, the aldol reaction of ester-derived sodium enolates with acetone, the unavoidable medium for dimethyldioxirane, could be totally suppressed by the use of the chlorotitanocene enolates 4.Thus, the oxidation of chiral titanium enolates by dimethyldioxirane represents a general, convenient, effective, and chemo- and diastereoselective synthesis of α-hydroxy carbonyl compounds.
- Adam, Waldemar,Mueller, Michael,Prechtl, Frank
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p. 2358 - 2364
(2007/10/02)
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- Highly Efficient Hydroxylation of Carbonyl Compounds with Dimethyldioxirane
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The enolates and/or enols of ketones, esters, β-diketones, β-oxo esters, and β-oxolactones were transformed by dimethyldioxirane (isolated in acetone solution or generated in situ) into their α-hydroxy compounds in good to excellent yields.The direct hydroxylation of the enols was significantly enhanced by the use of fluoride ion.For the enolate of camphor the exo/endo diastereoselectivity depended significantly on the metal ligand; the highest exo/endo ratio (93:7) was observed for the enol trimethylsilyl ether of camphor.Key Words: Dimethyldioxirane / Enolates / Hydroxylation / α-Hydroxy carbonyl compounds / Enol silyl ethers
- Adam, Waldemar,Prechtl, Frank
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p. 2369 - 2372
(2007/10/02)
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- Camphor-Derived Alcohols: An Anomalous Reaction of 3-Hydroxycamphor and the Influence of Internal Alkoxides on the Alkylation Stereochemistry of Glycinate Imines
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Attempted imine formation between 3-hydroxycamphor and tert. butyl glycinate led to 8, the substitution product at the 3-position.Zinc-acetic acid treatment of 8 afforded 3-acetoxycamphor.Alkylation of the imine from norcamphor and tert. butyl glycinate gave no stereoselection.Alkylation of the imine from 10-hydroxymethylcamphor and tert. butyl glycinate gave stereoselectivities inferior to those obtained from the imine of camphor itself (1), but aldol condensation with benzaldehyde, a reaction not possible with 1, was effected in 71percent yield.
- McIntosh, John M.,Cassidy, Kenneth C.,Matassa, Luca C.
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p. 5449 - 5458
(2007/10/02)
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- A Synthesis of the C6,C11-Dideoxyanthracyclinone Skeleton via Hassall Cyclization and Oxidative Desilylation
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A sequence of regiocontrolled Diels-Alder reactions has been used to prepare 15.Oxygenation of the benzylic silane in the presence of a fluoride source introduces the C7 hydroxyl group (95percent).Further conversion to the nitrile 21 followed by base-induced Hassall cyclization and oxidation gives the anthraquinone 25.Deprotection can be effected, but attempts to prepare 28 result in low yields.The oxygenation can be extended to certain enol silanes, but protodesilylation is a serious side reaction.
- Vedejs, E. V.,Pribish, J. R.
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p. 1593 - 1599
(2007/10/02)
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- Minor Products in Photoreactions of α-Diketones with Arenes. Abstraction of Hydroxylic Hydrogen by Triplet Carbonyl
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Photochemical reactions of cyclic saturated α-diketones in toluene or p-xylene produce 1:1 adducts as major products and smaller amounts of reduced diketone and bibenzyls, as expected from previous work.In addition, reaction of BOD gave 2percent of the decarbonylation product, p-methylbenzyl cyclohexyl ketone; reaction of camphorquinone gave a mixture of decarbonylation products (10percent total) including saturated and unsaturated monoketones.These compounds were secondary products arising from reaction of photoexcited diketone with the initially formed adducts; quenching andsensitization studies showed that triplet states of α-diketones were involved in both primary and secondary reactions.The decarbonylation products were also formed by reaction of benzophenone triplets or of tert-butoxy radicals with adducts.Deuterium labeling of the adducts was employed to demonstrate that the decarbonylation process involves abstraction of hydroxylic hydrogen.
- Rubin, Mordecai B.,Gutman, Arie L.
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p. 2511 - 2515
(2007/10/02)
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- Reduction by a Model of NAD(P)H. 32. Stereoselective Reduction of Camphoroquinone by a Chiral NAD(P)H Model
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(+)-, (-)-, and racemic camphoroquinones (CQ) were reduced by each of four NAD(P)H-models such as N-(α-methylbenzyl)-1-propyl-2,4-dimethyl-1,4-dihydronicotinamide (Me2PNPH) in the presence of magnesium ion in acetonitrile with a view to elucidating the intermolecular arrangement in the transition state for asymmetric reduction.Partial rate factors for each attacking mode were calculated.Electronegative substituents in the substrate prefer to facing the carbamoyl group in Me2PNPH, which is the most important factor determining the stereochemical course of the reduction. 1-Methyl group in CQ has a tendency to interfere with the dihydropyridine moiety in Me2PNPH approaching the C2-carbonyl group in CQ.This interference is more important for the selectivity than the intrinsic exo/endo reactivity difference.
- Ohno, Atsuyoshi,Goto, Takehiko,Nakai, Jun-ichi,Oka, Shinzaburo
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p. 3478 - 3481
(2007/10/02)
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- Reactions of Pivaloin Derivatives with Lithium Tetramethylpiperidide
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The reaction of lithium tetramethylpiperidide (LiTMP) with a series of derivatives of pivaloin has led to a variety of unusual transformations.The reaction of LiTMP with the triflate derivative of pivaloin (7) gave the reduced ketone 2,2,5,5-tetramethyl-3-hexanone (9), which is suggested to arise via electron transfer from LiTMP.A labeling study confirmed that α-proton abstraction from 7, giving an enolate anion, did not occur.The mesylate derivative of pivaloin (16) on treatment with LiTMP gave both isomers of 2,2,6,6-tetramethylhept-4-en-3-one (17 and 18) in which an additional carbon was incorporated into the carbon skeleton.A mechamism involving deprotonation of the methyl group of the mesyloxy function followed by intramolecular cyclization into the carbonyl function and subsequent reaction is suggested to account for this transformation.The acetate derivative of pivaloin (26) gave a cyclized product derived from proton abstraction from the methyl group of the acetoxy function, while the tosylate derivative of pivaloin (30) gave a product derived from proton abstraction from the ortho position of the aromatic ring.The α-bromo ketone 4-bromo-2,2,5,5-tetramethyl-3-hexanone (38) was reduced to ketone 9 with LiTMP.Reaction of triflate 7 and the triflate derivative of 3-hydroxycamphor (43) with potassium tert-butoxide gave the diketones 2,2,5,5-tetramethyl-3,4-hexanedione (8) and camphorquinone (44), respectively, by β elimination of trifluoromethanesulfinic acid.
- Creary, Xavier
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p. 2419 - 2425
(2007/10/02)
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