- STEREOCHEMISTRY OF 4-ARYL-2-BUTANOLS FROM HIMALAYAN TAXUS BACCATA
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4-(4'-Hydroxyphenyl)-2R-butanol, 4-(3',4'-dihydroxyphenyl)-2R-butanol and 4-(3'-methoxy-4'-hydroxyphenyl)-2R-butanol have been isolated from the needles of Himalayan Taxus baccata.These two compounds have not previously been reported in stereospecific forms.Their stereochemistry has been determined by enzymatic reduction of their corresponding 2-butanones.Key Word Index - Taxus baccata; Taxaceae; 4-aryl-2-butanol, stereochemistry; enzymatic reduction; baker's yeast.
- Das, B.,Takhi, M.,Kumar, H. M. Sampath,Srinivas, K. V. N. S.,Yadav, J. S.
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- Efficient production of raspberry ketone via 'green' biocatalytic oxidation
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For the development of a 'green' oxidation method, the transformation of 4-(p-hydroxyphenyl)butan-2-ol (rhododendrol) into 4-(p-hydroxyphenyl) butan-2-one (raspberry ketone) was used as a model reaction. Different lyophilized cells of Rhodococcus spp. have been screened for their ability to perform the desired oxidation. Rhodococcus equi IFO 3730 and R. ruber DSM 44541 were able to use acetone as a hydrogen acceptor in a hydrogen transfer-like process. The oxidation can be performed at substrate concentrations up to 500 g/L.
- Kosjek, Birgit,Stampfer, Wolfgang,Van Deursen, Ruud,Faber, Kurt,Kroutil, Wolfgang
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Read Online
- Deracemization and Stereoinversion of Alcohols Using Two Mutants of Secondary Alcohol Dehydrogenase from Thermoanaerobacter pseudoethanolicus
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We developed a one-pot sequential two-step deracemization approach to chiral alcohols using two mutants of Thermoanaerobacter pseudoethanolicus secondary alcohol dehydrogenase (TeSADH). This approach relies on consecutive non-stereospecific oxidation of alcohols and stereoselective reduction of their prochiral ketones using two mutants of TeSADH with poor and good stereoselectivities, respectively. More specifically, W110G TeSADH enables a non-stereospecific oxidation of alcohol racemates to their corresponding prochiral ketones, followed by W110V TeSADH-catalyzed stereoselective reduction of the resultant ketone intermediates to enantiopure (S)-configured alcohols in up to > 99 percent enantiomeric excess. A heat treatment after the oxidation step was required to avoid the interference of the marginally stereoselective W110G TeSADH in the reduction step; this heat treatment was eliminated by using sol-gel encapsulated W110G TeSADH in the oxidation step. Moreover, this bi-enzymatic approach was implemented in the stereoinversion of (R)-configured alcohols, and (S)-configured alcohols with up to > 99 percent enantiomeric excess were obtained by this Mitsunobu-like stereoinversion reaction.
- Hamdan, Samir M.,Musa, Musa M.,Nafiu, Sodiq A.,Takahashi, Etsuko,Takahashi, Masateru
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supporting information
(2020/07/24)
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- Deracemization of Secondary Alcohols by using a Single Alcohol Dehydrogenase
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We developed a single-enzyme-mediated two-step approach for deracemization of secondary alcohols. A single mutant of Thermoanaerobacter ethanolicus secondary alcohol dehydrogenase enables the nonstereoselective oxidation of racemic alcohols to ketones, followed by a stereoselective reduction process. Varying the amounts of acetone and 2-propanol cosubstrates controls the stereoselectivities of the consecutive oxidation and reduction reactions, respectively. We used one enzyme to accomplish the deracemization of secondary alcohols with up to >99 % ee and >99.5 % recovery in one pot and without the need to isolate the prochiral ketone intermediate.
- Karume, Ibrahim,Takahashi, Masateru,Hamdan, Samir M.,Musa, Musa M.
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p. 1459 - 1463
(2016/05/02)
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- Asymmetric synthesis of enantiomerically pure zingerols by lipase-catalyzed transesterification and efficient synthesis of their analogues
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The achiral zingerone 1, readily available from ginger, can be easily transformed into chiral derivatives. Zingerol 2, a reduced product of zingerone 1 is expected to be an important new medicinal lead compound. We have achieved a concise synthesis of optically active zingerol (R)-2 and (S)-2 by the lipase-catalyzed stereoselective transesterification of racemic 2. Under the optimized conditions, a lipase from Alcaligenes sp. (Meito QLM) and vinyl acetate in i-Pr2O or hexane at 35 C within 1 h gave the alcohol (S)-2 and the acetate (R)-9 with high enantioselectivity without producing acetylated by-products. Since optically active (S)-2 and (R)-9 were obtained through lipase-catalyzed transesterification, other enantiomerically pure novel compounds could all be synthesized.
- Kitayama, Takashi,Isomori, Sachiko,Nakamura, Kaoru
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p. 621 - 627
(2013/07/19)
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- Cephalosporolide B serving as a versatile synthetic precursor: Asymmetric biomimetic total syntheses of cephalosporolides C, E, F, G, and (4-OMe-)G
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Cephalosporolide B (Ces-B) was efficiently synthesized and exploited for the first time as a versatile biomimetic synthetic precursor for the chemical syntheses of not only cephalosporolides C, G, and (4-OMe-) G via a challenging diastereoselective oxa-Michael addition but also the structurally unprecedented cephalosporolides E and F via a novel biomimetic ring-contraction rearrangement. These findings provide the first direct chemical evidence that Ces-B may be the true biosynthetic precursor of cephalosporolides.
- Song, Liyan,Liu, Yuan,Tong, Rongbiao
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p. 5850 - 5853
(2013/12/04)
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- Concise enantioselective synthesis of the ten-membered lactone cephalosporolide G and its C-3 epimer
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A short and highly stereo-selective sequence for the first enantioselective total synthesis of the naturally occurring 10-membered lactone, which was obtained in only eight steps, was reported. The macrolactone ring was carried out by the use of a high-yielding pyridinium chlorochromate (PCC)-mediated oxidative cleavage of a bicyclic intermediate, generated in a domino sequence from a p-peroxyquinol. The synthesis was started with (-)-rhododendrol, which was obtained by enzymatic resolution of the racemic derivative. Phenol (R)-5 was submitted to an oxidative dearomatisation process with singlet oxygen, generated from Oxone in the presence of NaHCO3. The treatment of compound peroxyquinol with para-toluene sulfonic acid followed by Triton B gave, in one step and 49% yield, the tricyclic epoxide bicyclic derivative. A similar route was employed for the synthesis of the C-3 diastereoisomer of the natural product, which was obtained in only 7 steps and 15.2% overall yield.
- Barradas, Silvia,Urbano, Antonio,Carreno, M. Carmen
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body text
p. 9286 - 9289
(2010/04/03)
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- Orchestration of concurrent oxidation and reduction cycles for stereoinversion and deracemisation of sec-alcohols
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Black and white are opposites as are oxidation and reduction. Performing an oxidation, for example, of a sec-alcohol and a reduction of the corresponding ketone in the same vessel without separation of the reagents seems to be an impossible task. Here we show that oxidative cofactor recycling of NADP + and reductive regeneration of NADH can be performed simultaneously in the same compartment without significant interference. Regeneration cycles can be run in opposing directions beside each other enabling one-pot transformation of racemic alcohols to one enantiomer via concurrent enantioselective oxidation and asymmetric reduction employing defined alcohol dehydrogenases with opposite stereo- and cofactor-preference. Thus, by careful selection of appropriate enzymes, NADH recycling can be performed in the presence of NADP+ recycling to achieve overall, for example, deracemisation of sec-alcohols or stereoinversion representing a possible concept for a "green" equivalent to the chemical-intensive Mitsunobu inversion.
- Voss, Constance V.,Gruber, Christian C.,Faber, Kurt,Knaus, Tanja,Macheroux, Peter,Kroutil, Wolfgang
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supporting information; experimental part
p. 13969 - 13972
(2009/02/07)
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- Asymmetric synthesis of (R)-(-)-rhododendrol, the aglycone of the hepatoprotective agent rhododendrin
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Starting from 2,3-O-isopropylidene-D-glyceraldehyde (3) as chiral material, (R)-(-)-rhododendrol 2, the aglycone of the naturally occurring rhododendrin 1 was synthesized. Copyright Taylor & Francis Group, LLC.
- Sabitha, Gowravaram,Thirupathaiah,Yadav
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p. 1683 - 1688
(2008/02/01)
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- Resolution of racemic rhododendrol by lipase-catalyzed enantioselective acetylation
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Both (R)- and (S)-enantiomers of rhododendrol were prepared in high enantiomeric exess by lipase from Pseudomonas cepacia (Amano PS)-catalyzed acetylation of racemic 1 with vinyl acetate at room temperature. Especially, in the case of using acetonitrile as the solvent, by-products 4 and 5 were minimized.
- Yuasa, Yoshifumi,Shibuya, Shiroshi,Yuasa, Yoko
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p. 1469 - 1475
(2007/10/03)
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- Biogeneration and Biodegradation of Raspberry Ketone in the Fungus Beauveria bassiana
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In growing cultures of the fungus Beauveria bassiana (ATCC 7159) the incubation of 4-(4′-hydroxyphenyl)but-3-en-2-one (p-hydroxybenzylidenacetone, 3), of 4-(4′-hydroxyphenyl)butan-2-one (raspberry ketone, 1), and of the S and R,S forms of 4-(4′-hydroxyphenyl)butan-2-ol (2) yields 2-(4′-hydroxyphenyl)ethanol (tyrosol, 4) as a final product. The experiments support the view that the actual substrate for the Baeyer-Villiger-type degradation is raspberry ketone (1) and that there is a kinetic preference in the microbial enzymatic system for the oxidation to 1 of the S form of the 4-(4′-hydroxyphenyl)butan-2-ol (2).
- Fuganti, Claudio,Mendozza, Monica,Joulain, Daniel,Minut, Jose,Pedrocchi-Fantoni, Giuseppe,Piergianni, Valentino,Servi, Stefano,Zucchi, Gioia
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p. 3616 - 3619
(2007/10/03)
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- Isolation of taxol, 10-deacetylbaccatin III and (-)-betuligenol from Taxus baccata Linn.
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Taxol (1), 10-deacetylbaccatin III (2) (-)-betuligenol (3), p-hydroxybenzaldehyde (4) and betuloside (5) have been isolated from Taxus baccata Linn. of Indian variety.
- Chattopadhyay, S. K.,Tripathi, V. K.,Thakur, R. S.,Sharma, R. P.,Jain, S. P.
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p. 409 - 411
(2007/10/02)
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- Catalytic asymmetric induction part 2. Chiral tricarbonyl (η6 arene) chromium (O) complexes as enantioselective catalysts
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A chiral metallocyclic Lewis acid based catalyst system derived from norephedrine is reported. A key stereodirective element emanates from a tricarbonyl chromium (O) group complexed to the aryl ring. The catalysts mediate the addition of dialkyl zinc species to a variety of aldehydes with high enantioselectivity.
- Jones,Heaton
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p. 261 - 272
(2007/10/02)
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- Synthesis of rhododendrin and epi-rhododendrin,
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The first synthesis of rhododendrin 1 and epi-rhododendrin 2 was achieved by starting from ethyl (S)-3-hydroxybutanoate 4, p-bromoanisole and D-glucose.Rhododendrin 1 is known as the hepatoprotective constituent of Taxus baccata L. Keywords: betuligenol / betuloside / epi-rhododendrin / rhododendrin / rhododendrol
- Mori, Kenji,Qian, Zhao-Hui
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p. 382 - 387
(2007/10/02)
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- Absolute Configuration of epi-Rhododendrin and (-)-Rhododendrol and X-Ray Crystal and Molecular Structure of Rhododendrin , a Hepatoprotective Constituent of Taxus baccata
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Rhododendrin (= betuloside) has been isolated from the leaves of Taxus baccata L.From its X-ray diffraction studies, the absolute configuration at the chiral centre in the aglucone portion has been found to be R.These results establish the stereochemical assignments to different samples of this glucoside isolated from different plants.Our sample of rhododendrin exhibited hepatoprotective activity against two hepatotoxins in rats.
- Parmar, Virinder S.,Vardhan, Anand,Taneja, Poonam,Sinha, Rita,Patnaik, Gyanendra K.,et al.
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p. 2687 - 2690
(2007/10/02)
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- Studies on the Constituents of Aceraceae Plants. V. Two Diarylheptanoid glycosides and an Arylbutanol Apiosylglucoside from Acer nikoense
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From the stem bark of Acer nikoense Maxim. (Aceraceae), three glycosides were isolated, namely aceroside III (1), C30H40O12, mp 138-141 deg C, D -98.4 deg, aceroside VI (2), C25H32O8*1/2H2O, mp 124-125 deg C, D -69.3 deg, and apiosylepirhododendrin (3), amorphous film (C21H32O11), D -59.5 deg.On acid hydrolysis, 1 yielded acerogenin A (4), apiose, glucose, and a partially hydrolyzed product 2, while 3 afforded (+)-rhododendrol (11), apiose, and glucose.Inspection of the carbon-13 nuclear magnetic resonance (13C NMR) and the PRFT-NMR spectra of 1 and 3 disclosed that they are apiosyl-(1->6)-glucosides.The proton nuclear magnetic resonance (1H NMR) spectral data of their permethylates (6 and 12) and the analytical data of methanolysis products of 6 and 12 established the structures of 1, 2 and 3 as acerogenin A 11-O-β-D-apiofuranosyl-(1->6)-β-D-glucopyranoside, acerogenin A 11-O-β-D-glucopyranoside and (+)-rhododendrol 2-O-β-D-apiofuranosyl-(1->6)-β-D-glucanopyranoside, respectively.Keywords - Acer nikoense; Aceraceae; diarylheptanoid; arylbutanol; apiosylglucoside; aceroside (III, VI); apiosylepirhododendrin; (+)-rhododendrol; PRFT-NMR
- Nagai, Masahiro,Kubo, Masayoshi,Takahashi, Kunio,Fujita, Masao,Inoue, Takao
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p. 1923 - 1928
(2007/10/02)
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