- Enantioselective synthesis of pure (R,R)-2,3-butanediol in Escherichia coli with stereospecific secondary alcohol dehydrogenases
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We characterized the activity and stereospecificity of four secondary alcohol dehydrogenases (sADHs) towards acetoin reduction and constructed synthetic pathways in E. coli to produce enantiomerically pure (R,R)-2,3-butanediol (2,3-BDO) from glucose with
- Yan, Yajun,Lee, Chia-Chi,Liao, James C.
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- Engineering Pichia pastoris for improved NADH regeneration: A novel chassis strain for whole-cell catalysis
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Many synthetically useful reactions are catalyzed by cofactor-dependent enzymes. As cofactors represent a major cost factor, methods for efficient cofactor regeneration are required especially for large-scale synthetic applications. In order to generate a novel and efficient host chassis for bioreductions, we engineered the methanol utilization pathway of Pichia pastoris for improved NADH regeneration. By deleting the genes coding for dihydroxyacetone synthase isoform 1 and 2 (DAS1 and DAS2), NADH regeneration via methanol oxidation (dissimilation) was increased significantly. The resulting Δdas1 Δdas2 strain performed better in butanediol dehydrogenase (BDH1) based whole-cell conversions. While the BDH1 catalyzed acetoin reduction stopped after 2 h reaching ～50% substrate conversion when performed in the wild type strain, full conversion after 6 h was obtained by employing the knockout strain. These results suggest that the P. pastoris Δdas1 Δdas2 strain is capable of supplying the actual biocatalyst with the cofactor over a longer reaction period without the over-expression of an additional cofactor regeneration system. Thus, focusing the intrinsic carbon flux of this methylotrophic yeast on methanol oxidation to CO2 represents an efficient and easy-to-use strategy for NADH-dependent whole-cell conversions. At the same time methanol serves as co-solvent, inductor for catalyst and cofactor regeneration pathway expression and source of energy.
- Geier, Martina,Brandner, Christoph,Strohmeier, Gernot A.,Hall, Mélanie,Hartner, Franz S.,Glieder, Anton
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- Asymmetric hydroboration of [E]- and [Z]-2-methoxy-2-butenes. Synthesis of (-)-[2R,3R]-butane-2,3-diol in >97% ee
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Asymmetric hydroboration of [E]- and [Z]-2-methoxy-2-butene, using (-)-diisopinocampheylborane at -25°C in THF solvent, followed by oxidation using H2O2/NaOH, gave (-)-[2R,3R]- and (+)-[2R,3S]-3-methoxy-2-butanols in >97 and 90% ee,
- Murali, Dhanabalan,Singaram, Bakthan,Brown, Herbert C.
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- Application of robust ketoreductase from Hansenula polymorpha for the reduction of carbonyl compounds
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Enzyme-catalysed asymmetric reduction of ketones is an attractive tool for the production of chiral building blocks or precursors for the synthesis of bioactive compounds. Expression of robust ketoreductase (KRED) from Hansenula polymorpha was upscaled and applied for the asymmetric reduction of 31 prochiral carbonyl compounds (aliphatic and aromatic ketones, diketones and β-keto esters) to the corresponding optically pure hydroxy compounds. Biotransformations were performed with the purified recombinant KRED together with NADP+ recycling glucose dehydrogenase (GDH, Bacillus megaterium), both overexpressed in Escherichia coli BL21(DE3). Maximum activity of KRED for biotransformation of ethyl-2-methylacetoacetate achieved by the high cell density cultivation was 2499.7 ± 234 U g–1DCW and 8.47 ± 0.40 U·mg–1E, respectively. The KRED from Hansenula polymorpha is a very versatile enzyme with broad substrate specificity and high activity towards carbonyl substrates with various structural features. Among the 36 carbonyl substrates screened in this study, the KRED showed activity with 31, with high enantioselectivity in most cases. With several ketones, the Hansenula polymorpha KRED catalysed preferentially the formation of the (R)-secondary alcohols, which is highly valued.
- Petrovi?ová, Tatiana,Gyuranová, Dominika,Pl?, Michal,Myrtollari, Kamela,Smonou, Ioulia,Rebro?, Martin
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- Synthesis of α-hydroxy ketones and vicinal (R, R)-diols by Bacillus clausii DSM 8716T butanediol dehydrogenase
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α-hydroxy ketones (HK) and 1,2-diols are important building blocks for fine chemical synthesis. Here, we describe the R-selective 2,3-butanediol dehydrogenase from B. clausii DSM 8716T (BcBDH) that belongs to the metal-dependent medium chain dehydrogenases/reductases family (MDR) and catalyzes the selective asymmetric reduction of prochiral 1,2-diketones to the corresponding HK and, in some cases, the reduction of the same to the corresponding 1,2-diols. Aliphatic diketones, like 2,3-pentanedione, 2,3-hexanedione, 5-methyl-2,3-hexanedione, 3,4-hexanedione and 2,3-heptanedione are well transformed. In addition, surprisingly alkyl phenyl dicarbonyls, like 2-hydroxy-1-phenylpropan-1-one and phenylglyoxal are accepted, whereas their derivatives with two phenyl groups are not substrates. Supplementation of Mn2+ (1 mM) increases BcBDH's activity in biotransformations. Furthermore, the biocatalytic reduction of 5-methyl-2,3-hexanedione to mainly 5-methyl-3-hydroxy-2-hexanone with only small amounts of 5-methyl-2-hydroxy-3-hexanone within an enzyme membrane reactor is demonstrated.
- Bongaerts, Johannes,Jablonski, Melanie,Kipp, Carina Ronja,Molinnus, Denise,Muschallik, Lukas,Pohl, Martina,Sch?ning, Michael J.,Selmer, Thorsten,Siegert, Petra,Wagner, Torsten
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p. 12206 - 12216
(2020/04/20)
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- Highly efficient and recyclable chiral Pt nanoparticle catalyst for enantioselective hydrogenation of activated ketones
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Thermoregulated phase-separable chiral Pt nanoparticle catalyst exhibited excellent ee (>99%) in the enantioselective hydrogenation of activated ketones for preparing chiral α-hydroxy acetals and chiral 1,2-diols. More importantly, the chiral catalyst could be easily separated by phase separation and directly reused in the next cycle without any loss in catalytic activity and enantioselectivity, even in the gram-scale reaction. The leaching of Pt was under the detection limit of the instrument.
- Xue, Xiuru,Chen, Pu,Xu, Peng,Wang, Yanhua
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- Biocatalytic production of alpha-hydroxy ketones and vicinal diols by yeast and human aldo-keto reductases
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The α-hydroxy ketones are used as building blocks for compounds of pharmaceutical interest (such as antidepressants, HIV-protease inhibitors and antitumorals). They can be obtained by the action of enzymes or whole cells on selected substrates, such as diketones. We have studied the enantiospecificities of several fungal (AKR3C1, AKR5F and AKR5G) and human (AKR1B1 and AKR1B10) aldo-keto reductases in the production of α-hydroxy ketones and diols from vicinal diketones. The reactions have been carried out with pure enzymes and with an NADPH-regenerating system consisting of glucose-6-phosphate and glucose-6-phosphate dehydrogenase. To ascertain the regio and stereoselectivity of the reduction reactions catalyzed by the AKRs, we have separated and characterized the reaction products by means of a gas chromatograph equipped with a chiral column and coupled to a mass spectrometer as a detector. According to the regioselectivity and stereoselectivity, the AKRs studied can be divided in two groups: one of them showed preference for the reduction of the proximal keto group, resulting in the S-enantiomer of the corresponding α-hydroxy ketones. The other group favored the reduction of the distal keto group and yielded the corresponding R-enantiomer. Three of the AKRs used (AKR1B1, AKR1B10 and AKR3C1) could produce 2,3-butanediol from acetoin. We have explored the structure/function relationships in the reactivity between several yeast and human AKRs and various diketones and acetoin. In addition, we have demonstrated the utility of these AKRs in the synthesis of selected α-hydroxy ketones and diols.
- Calam, Eduard,Porté, Sergio,Fernández, M. Rosario,Farrés, Jaume,Parés, Xavier,Biosca, Josep A.
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p. 195 - 203
(2013/05/08)
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- Three new fatty acid esters from the mushroom Boletus pseudocalopus
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A bioassay-guided fractionation and chemical investigation of a MeOH extract of the Korean wild mushroom Boletus pseudocalopus resulted in the identification of three new fatty acid esters, named calopusins A-C (1-3), along with two known fatty acid methyl esters (4-5). These new compounds are structurally unique fatty acid esters with a 2,3-butanediol moiety. Their structures were elucidated through 1D- and 2D-NMR spectroscopic data and GC-MS analysis as well as a modified Mosher's method. The new compounds 1-3 showed significant inhibitory activity against the proliferation of the tested cancer cell lines with IC50 values in the range 2.77-12.51 μM. AOCS 2011.
- Kim, Ki Hyun,Choi, Sang Un,Lee, Kang Ro
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experimental part
p. 593 - 599
(2012/09/10)
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- Modular monodentate oxaphospholane ligands: Utility in highly efficient and enantioselective 1,4-diboration of 1,3-dienes
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Tune it up! Tunable, chiral, monodentate oxaphospholane ligands (termed OxaPhos) are highly effective in the Pt-catalyzed title reaction, providing the 1,4-addition products in enantiomer ratios approaching 99:1 (see scheme). In the presence of enantiomerically pure cis-iBu-OxaPhos, a catalyst loading of only 0.02 mol% [Pt(dba)3] was sufficient for effective reaction. pin=pinacolato, dba=dibenzylideneacetone.
- Schuster, Christopher H.,Li, Bo,Morken, James P.
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supporting information; scheme or table
p. 7906 - 7909
(2011/10/09)
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- Manipulating the stereoselectivity of limonene epoxide hydrolase by directed evolution based on iterative saturation mutagenesis
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Limonene epoxide hydrolase from Rhodococcus erythropolis DCL 14 (LEH) is known to be an exceptional epoxide hydrolase (EH) because it has an unusual secondary structure and catalyzes the hydrolysis of epoxides by a rare one-step mechanism in contrast to the usual two-step sequence. From a synthetic organic viewpoint it is unfortunate that LEH shows acceptable stereoselectivity essentially only in the hydrolysis of the natural substrate limonene epoxide, which means that this EH cannot be exploited as a catalyst in asymmetric transformations of other substrates. In the present study, directed evolution using iterative saturation mutagenesis (ISM) has been tested as a means to engineer LEH mutants showing broad substrate scope with high stereoselectivity. By grouping individual residues aligning the binding pocket correctly into randomization sites and performing saturation mutagenesis iteratively using a reduced amino acid alphabet, mutants were obtained which catalyze the desymmetrization of cyclopentene-oxide with stereoselective formation of either the (R,R)- or the (S,S)-diol on an optional basis. The mutants prove to be excellent catalysts for the desymmetrization of other meso-epoxides and for the hydrolytic kinetic resolution of racemic substrates, without performing new mutagenesis experiments. Since less than 5000 tranformants had to be screened for achieving these results, this study contributes to the generalization of ISM as a fast and reliable method for protein engineering. In order to explain some of the stereoselective consequences of the observed mutations, a simple model based on molecular dynamics simulations has been proposed.
- Zheng, Huabao,Reetz, Manfred T.
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supporting information; experimental part
p. 15744 - 15751
(2011/02/21)
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- Rhodotorula minuta-mediated bioreduction of 1,2-diketones
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The reduction of cyclic and acyclic 1,2-diketones was investigated by employing whole cells of the yeast Rhodotorula minuta as biocatalyst. The reactions showed a variable degree of regio- and enantioselectivity depending on the nature of the substrate. In the case of cyclic diketones, the reduction afforded a mixture of diastereomeric diols only. The reduction of acyclic diketones allowed production of both the hydroxy ketone and the diol, in a two-step reaction. The first step was highly regio- and stereoselective, affording the hydroxy ketone of (S)-configuration with high enantiomeric excess. After longer reaction times the corresponding (S,S)-diols were obtained in high yield and diastereomeric excess.
- Monsalve, Leandro N.,Cerrutti, Patricia,Galvagno, Miguel A.,Baldessari, Alicia
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experimental part
p. 137 - 143
(2011/11/12)
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- A comparative study of the relative stability of representative chiral and achiral boronic esters employing transesterification
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A comparative study of the transesterification of five representative chiral and achiral boronic esters with various structurally modified diols was undertaken to qualitatively understand the factors influencing the relative stability of these boronic esters. Several factors such as chelation, conformation, steric bulk of the substituents, size of the heterocycle, and entropy influence the relative rate of transesterification as well as the stability of the boronic esters. Amongst these boronic esters, pinanediol phenylboronic ester was found to be the most stable boronic ester whereas DIPT boronic ester appeared to be thermodynamically the least stable one. The transesterification with sterically hindered diols was observed to be relatively slow, but afforded thermodynamically more stable boronic esters. Boronic esters derived from cis-cyclopentanediols and the bicyclo[2.2.1]heptane-exo,exo-2,3- diols are relatively more stable. This study not only presents the qualitative picture of relative stability of various boronic esters, but also provides helpful hints regarding the possible recovery of chiral auxiliaries. Many C 2-symmetric chiral auxiliaries, such as 2,3-butanediol, 2,4-pentanediol, DIPT, and cis-cyclohexane-1,2-diol, can be retrieved by simple transesterification of the corresponding boronic esters with commercial inexpensive diols, such as pinacol, 1,3-propanediol, and neopentyl glycol.
- Roy, Chandra D.,Brown, Herbert C.
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p. 879 - 887
(2008/02/11)
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- Direct proline-catalyzed asymmetric α-aminoxylation of aldehydes and ketones
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The direct proline-catalyzed asymmetric α-aminoxylation of aldehydes and ketones has been developed using nitrosobenzene as an oxygen source, affording α-anilinoxy-aldehydes and -ketones with excellent enantioselectivity. Reaction conditions have been optimized, and low temperature (-20 °C) was found to be a key for the successful α-aminoxylation of aldehydes, while slow addition of nitrosobenzene is essential for that of ketones. The scope of the reaction is presented.
- Hayashi, Yujiro,Yamaguchi, Junichiro,Sumiya, Tatsunobu,Hibino, Kazuhiro,Shoji, Mitsuru
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p. 5966 - 5973
(2007/10/03)
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- DERMATOLOGICAL COMPOSITIONS AND METHODS
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Disclosed are methods and compositions for regulating the melanin content of mammalian melanocytes; regulating pigmentation in mammalian skin, hair, wool or fur; treating or preventing various skin and proliferative disorders; by administration of various compounds, including alcohols, diols and/or triols and their analogues.
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- Chemoenzymatic preparation of (2S,3S)- and (2R,3R)-2,3-butanediols and their esters from mixtures of d,l- and meso-diols
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An efficient method of preparing the pure enantiomers of 2,3-butanediol from commercially available mixtures of the d,l- and meso-isomers was developed. It furnished (2S,3S)-2,3-butanediol with >99% e.e. and a >99.5/0.5 diastereomeric ratio and (2R,3R)-2,3-butanediol in 95% e.e. and >95/5 diastereomeric ratio.
- Liu, Rong,Hoegberg, Hans-Erik
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p. 771 - 778
(2007/10/03)
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- Asymmetric hydrosilylation of ketones using trans-chelating chiral peralkylbisphosphine ligands bearing primary alkyl substituents on phosphorus atoms
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Asymmetric hydrosilylation of simple ketones with diphenylsilane proceeded at -40 °C in the presence of a rhodium complex (0.001 - 0.01 molar amount) coordinated with a trans-chelating chiral bisphosphine ligand bearing linear alkyl substituents on the phosphorus atoms, (R,R)-(S,S)-Et-, Pr-, or BuTRAP, giving the corresponding optically active (S)- secondary alcohols with up to 97% ee. The asymmetric hydrosilylation using TRAP ligands with bulkier P-substituents resulted in much lower enantioselectivities. The EtTRAP-rhodium catalyst was also effective for asymmetric hydrosilylation of keto esters with a coordination site for a rhodium atom (up to 98% ee). Optically active symmetrical diols were obtained with up to 99% ee from the corresponding diketones via the asymmetric reduction using 2.5 molar amounts of diphenylsilane.
- Kuwano, Ryoichi,Sawamura, Masaya,Shirai, Junya,Takahashi, Masatoshi,Ito, Yoshihiko
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p. 485 - 496
(2007/10/03)
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- Highly enantioselective preparation of C2-symmetrical diols: Microbial hydrolysis of cyclic carbonates
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A new type of microbial enantioselective hydrolysis of C2-symmetrical cyclic carbonates is disclosed. During the screening test of the five-membered substrate (4,5-dimethyl-1,3-dioxolan-2-one 5), Pseudomonas diminuta was selected as the best strain to perform the stereoselective hydrolysis. The reaction of dl-5 with this microorganism in aqueous media containing THF as the co-solvent afforded (S,S)-5 and (R,R)-butanediol 1 in excellent yields. It was found that the ring size did not affect the reactivity and enantioselectivity although the enzyme had a high substrate specificity for the side chain. A six-membered cyclic carbonate, dl-4,6-dimethyl-1,3-dioxan-2-one 6, was smoothly hydrolyzed with higher enantioselectivity to afford the optically active (S,S)-6 and (R,R)-2,4-pentanediol 2. Copyright (C) 2000 Elsevier Science Ltd.
- Matsumoto, Kazutsugu,Sato, Youichi,Shimojo, Megumi,Hatanaka, Minoru
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p. 1965 - 1973
(2007/10/03)
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- Treatment of neurodegenerative diseases
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Disclosed are methods for increasing the differentiation of mammalian neuronal cells for purposes of treating neurodegenerative diseases or nerve damage by administration of various compounds including alcohols, diols and/or triols and their analogues.
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- Treatment of diseases mediated by the nitric oxide/cGMP/protein kinase G pathway
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Disclosed are methods and compositions for stimulating cellular nitric oxide (NO) synthesis, cyclic guanosine monophosphate levels (cGMP), and protein kinase G (PKG) activity for purposes of treating diseases mediated by deficiencies in the NO/cGMP/PKG signal transduction pathway, by administration of various compounds including alcohols, diols and/or triols and their analogues.
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- Hydrogenation of butane-2,3-dione with heterogeneous cinchona modified platinum catalysts: A combination of an enantioselective reaction and kinetic resolution
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(R)-3-Hydroxybutan-2-one was obtained with 85-90% ee albeit in low yield by the Pt/Al2O3 cinchona catalyzed hydrogenation of butane-2,3-dione by a combination of enantioselective hydrogenation and kinetic resolution.
- Studer, Martin,Okafor, Victor,Blaser, Hans-Ulrich
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p. 1053 - 1054
(2007/10/03)
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- Enantioselective Hydrogenation: V. Hydrogenation of Butane-2,3-dione and of 3-Hydroxybutan-2-one Catalysed by Cinchona-Modified Platinum
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Pt/silica modified by cinchonidine and cinchonine is active for the enantioselective hydrogenation of butane-2,3-dione to butane-2,3-diol in dichloromethane at 268-298 K and 10 bar pressure. Reaction proceeds in three stages. In the first, about 85% of the butane-2,3-dione is converted to 3-hydroxybutan-2-one and 15% to three higher molecular weight products by hydrodimerisation. The initial enantiomeric excess in the hydroxybutanone is modest (20 to 40%(R) with cinchonidine as modifier, 10%(S) with cinchonine as modifier) and dependent on the amount of alkaloid used in catalyst preparation. In the second stage, 3-hydroxybutan-2-one is converted to butane-2,3-diol; a marked kinetic effect is observed whereby the minority enantiomer is converted preferentially to butanediol and the enantiomeric excess in the remaining hydroxybutanone increases dramatically to values in the range 62 to 89%(R) and to 30%(S). Under all conditions, the most abundant stereochemical form of the final product is meso-butane-2,3-dione. In the third stage the three dimers are slowly converted by hydrogenation, dissociation, and further hydrogenation to butane-2,3-diol. In the absence of alkaloid, butane-2,3-dione hydrogenation to racemic products in dichloromethane solution proceeds in two distinct stages with no dimer formation. Butane-2,3-dione hydrogenation has also been studied over Pt/silica modified anaerobically by exposure to cinchonidine in ethanol under propyne at 2 bar. This catalyst is remarkably active for the conversion of diketone to diol in ethanol at 293 K and 10 bar and kinetic selection in the second stage of reaction is again observed. The hydrogenation of racemic 3-hydroxybutan-2-one in dichloromethane over cinchonine-modified Pt/silica at 273 K and 10 to 40 bar pressure also showed kinetic selection, an enantiomeric excess of up to 70%(S) appearing in the reactant as it was consumed. Mechanisms which account for these hydrogenations and dimerisations and for the enantioselectivities observed and their variation are presented. This diketone hydrogenation provides an example of consecutive thermodynamic and kinetic control of enantioselectivity in a multistage catalytic reaction.
- Slipszenko,Griffiths,Johnston,Simons,Vermeer,Wells
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p. 267 - 276
(2007/10/03)
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- An improved synthesis of chiral diols via the asymmetric catalytic hydrogenation of prochiral diones
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The rates of the asymmetric hydrogenation of prochiral diketones catalyzed by Ru(BINAP) catalysts were substantially accelerated in the presence of small amounts of a strong acid.
- Fan, Qing-Hua,Yeung, Chi-Hung,Chan, Albert S. C.
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p. 4041 - 4045
(2007/10/03)
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- Conversion of meso-2,3-Butanediol into 2-Butanol by Lactobacilli. Stereochemical and Enzymatic Aspects
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A number of strains of Lactobacillus spp. from foods were screened for their ability to convert meso-2,3-butanediol into 2-butanol. Only three strains of L. brevis transformed the meso-diol into the secondary alcohol. These strains as well as the others unable to metabolize meso-2,3-butanediol exhibited the capacity to hydrogenate 2-butanone to 2-butanol. In both types of lactobacilli, an inverse relationship was observed between the diol or ketone concentration and the abundance of the R form of 2-butanol. This fact has been interpreted in terms of a co-occurrence of two dehydrogenases, both acting on the ketone with different kinetic parameters and opposite enantioselectivities. These results represent a further support to the assumption that 2-butanol present in distillates originates from the enzymatic activity of lactobacilli growing on mashes and give the most likely explanation of the enantiomeric excess of (R)-2-butanol generally found in distillates.
- Speranza, Giovanna,Corti, Sandra,Fontana, Gabriele,Manitto, Paolo,Galli, Antonietta,Scarpellini, Mauro,Chialva, Franco
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p. 3476 - 3480
(2007/10/03)
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- Enantioselective hydrolysis of aryl, alicyclic and aliphatic epoxides by Rhodotorula glutinis
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Enantioselective epoxide hydrolysis by yeasts has been demonstrated for the hydrolysis of several aryl, alicyclic and aliphatic epoxides by a strain of Rhodotorula glutinis. High enantioselectivity was obtained in the hydrolysis of methyl substituted aryl and aliphatic epoxides whereas selectivity towards terminal epoxides in all cases was lower. Homochiral vicinal diols were formed from several methyl substituted epoxides and also from meso epoxides. Kinetic resolution of trans-1-phenyl-1,2-epoxypropane was studied in more detail.
- Weijers, Carel A. G. M.
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p. 639 - 647
(2007/10/03)
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- Yeast-mediated synthesis of optically active diols with C2-symmetry and (R)-4-pentanolide
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Reduction of some diketones and a keteacid with yeast, Pichia farinosa IAM 4682 was examined. The reduction of carbonyl groups proceeded highly selectively with an anti-Prelog fashion to give (R)-alcohols. (2R,5R)2,5- Hexanediol (83% yd., >99% e.e., 95% d.e.), (2R,4R)-2,4-pentanediol (94% yd., >99% e.e., 98% d.e.), and (R)-4-pentanolide (67% yd., >99% e.e.) were highly efficiently obtained from the corresponding ketones. Effect of the structure of substrate on the stereochemical course as well as the selectivity were discussed.
- Ikeda,Sato,Sugai,Ohta
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p. 8113 - 8122
(2007/10/03)
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- Asymmetric Hydrosilylation of Symmetrical Diketones Catalyzed by a Rhodium Complex with Trans-Chelating Chiral Diphosphine EtTRAP
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Asymmetric hydrosilylation of symmetrical diketones with diphenylsilane in the presence of catalytic amount (/ = 100> of rhodium complex coordinated with trans-chelating chiral phosphine ligand EtTRAP gave corresponding optically active symmetrical diols with high enantiomeric excesses.
- Kuwano, Ryoichi,Sawamura, Masaya,Shirai, Junya,Takahashi, Masatoshi,Ito, Yoshihiko
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p. 5239 - 5242
(2007/10/02)
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- Efficient Rhodium-Catalyzed Hydrogenation of Aldehydes and Ketones
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A cationic rhodium(I) catalyst bearing the air-stable and crystalline diphosphine 1,1'-bis-(diisopropylphosphino)ferrocene (1, DiPFc) allows the hydrogenation of aldehydes and ketones under mild conditions.
- Burk, Mark J.,Harper, T. Gregory P.,Lee, Jeffrey R.,Kalberg Christopher
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p. 4963 - 4966
(2007/10/02)
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- Intermediates for preparing optically active carboxylic acids
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A process is described for preparing optically active alpha-arylalkanoic acids consisting of rearranging an optically active ketal of formula STR1 in which the substituents have the meaning given in the description of the invention.
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- CHIRAL SYNTHESIS OF ISOCARBACYCLIN -9-METHANO-Δ6-PGI1> INTERMEDIATE VIA RHODIUM-CATALYZED INTRAMOLECULAR C-H INSERTION REACTION
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A key intermediate for the synthesis of isocarbacyclin, a promising therapeutic agent for cardiovascular and circulatory disorders, has been synthesized from (R)-(+)-methyl 2-oxo-1-cyclopentaneacetate by employing rhodium(II)-catalyzed intramolecular C-H insertion reaction of α-diazo β-keto ester as a key step.
- Hashimoto, Shun-ichi,Shinoda, Tomohiro,Shimada, Yasunaga,Honda, Takeshi,Ikegami, Shiro
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p. 637 - 640
(2007/10/02)
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- Empirical force field calculations. Part 28. Conformations and pseudorotations of 1,3-dioxolane and some methyl-substituted derivatives
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The conformations and pseudorotations of 1,3-dioxolane(1), cis- and trans-4,5-dimethyl-1,3-dioxolane (2 and 3) and the corresponding 2,2-dimethyl derivatives (4, 5 and 6) have been studied with molecular mechanics using the MM2 force field.Free pseudorotation occurs in 1 and 4 (ΔE = 1.5 kJ/mol) and pseudolibration in 2, 3, 5 and 6 (ΔE = 6, 7, 11 and 14 kJ/mol, respectively).The steric energies of 3 and 6 are lower than those of 2 and 5 since the 4- and 5-methyl groups can both occupy a pseudo-equatorial position in the minimum energy conformation of the trans isomers.Estimates of ΔH0f (25 deg C, gas, kJ/mol) are: 2, -376.1; 3, -380.5; 4, -387.2; 5, -464.4; 6, -470.1.Vicinal proton coupling constants were calculated from the appropriate torsion angles and averaged over the pseudorotation circuit. they are in good agreement with experimental values.The 1,3-dioxolanes can be used as model compounds for borate monoesters of vicinal diols.The 13C chemical shifts of C(2) in 1,3-dioxolanes correlate well with the 11B chemical shifts in the corresponding borate monoesters.
- Duin, M. van,Hoefnagel, M. A.,Baas, J. M. A.,Graaf, B. van de
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p. 607 - 612
(2007/10/02)
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- DETERMINATION DE PURETE ENANTIOMERIQUE PAR RMN13C DANS LES SERIES DES BICYCLO(2.2.1.)-HEPTANE ET BICYCLO(2.2.1.)-HEPTENE
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N.M.R.13C peak assignments were established for each diastereoisomeric ketal form of norbornanone (+/-), or norbornenone (+/-).This method offers an attractive route for the determination of the optical purity of these ketones.
- Bordeaux, D.,Gagnaire, G.
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p. 3353 - 3356
(2007/10/02)
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