- Structural and functional insights into asymmetric enzymatic dehydration of alkenols
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The asymmetric dehydration of alcohols is an important process for the direct synthesis of alkenes. We report the structure and substrate specificity of the bifunctional linalool dehydratase isomerase (LinD) from the bacterium Castellaniella defragrans that catalyzes in nature the hydration of β-myrcene to linalool and the subsequent isomerization to geraniol. Enzymatic kinetic resolutions of truncated and elongated aromatic and aliphatic tertiary alcohols (C5-C15) that contain a specific signature motif demonstrate the broad substrate specificity of LinD. The three-dimensional structure of LinD from Castellaniella defragrans revealed a pentamer with active sites at the protomer interfaces. Furthermore, the structure of LinD in complex with the product geraniol provides initial mechanistic insights into this bifunctional enzyme. Site-directed mutagenesis confirmed active site amino acid residues essential for its dehydration and isomerization activity. These structural and mechanistic insights facilitate the development of hydrating catalysts, enriching the toolbox for novel bond-forming biocatalysis.
- Nestl, Bettina M.,Geinitz, Christopher,Popa, Stephanie,Rizek, Sari,Haselbeck, Robert J.,Stephen, Rosary,Noble, Michael A.,Fischer, Max-Philipp,Ralph, Erik C.,Hau, Hoi Ting,Man, Henry,Omar, Muhiadin,Turkenburg, Johan P,Van Dien, Stephen,Culler, Stephanie J.,Grogan, Gideon,Hauer, Bernhard
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p. 275 - 281
(2017/02/23)
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- Characterization of vinyl-substituted, carbon-carbon double bonds by GC/FT-IR analysis.
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Vapor-phase infrared spectra allow the determination of the stereochemistry of carbon-carbon double bonds conjugated with a vinyl group. Cis and trans isomers of unsubstituted 1,3-alkadienes can be differentiated on the basis of the differences observed in the 900-1000 cm-1 region (spectra of cis isomers show two bands at 993 and 906 cm-1, while those of trans compounds show three absorptions at 998, 949, and 902 cm-1) and the 1590-1650 cm-1 region (the C=C stretch bands are observed at 1595 and 1642 cm-1 for cis compounds and at 1604 and 1650 cm-1 for trans compounds). Compounds bearing CH2=CHC(CH3)=CHCH2- and CH2=CHC(=CH2)-CH2- structural moieties, referred to as alpha- and beta-type compounds, are frequently encountered as natural products. For compounds bearing alpha-type groups, the cis/trans configuration of the trisubstituted double bond can be determined unambiguously. An absorption at 3095-3091 cm-1, for the =CH2 stretch vibration, is common to both of these groups; however, due to the presence of two =CH2 groups, the relative intensity of the band is much higher for beta-type compounds. For alpha-type compounds, a cis configuration at the C-3 carbon atom is characterized by a =CH2 wag absorption at 907-906 cm-1. For beta-type compounds and 3E-alpha-type compounds, this band appears at 899-897 cm-1. In addition, a wavy "fingerprint" pattern with two minima at 1632 (low intensity) and 1595-1594 cm-1 (high intensity) is characteristic for beta-type compounds. Our generalizations are based on spectra of cis and trans ocimene, myrcene, and dehydration products of many 3-methyl-1-alken-3-ols. Six isomers of farnesene can be characterized by GC/FT-IR. Furthermore, gas-phase IR allows the determination of the configuration of the trisubstituted double bond at C-3 in alpha-type farnesene congeners. For example, the homo- and bishomofarnesene isomers from Myrmica ants were shown to include a 3Z bond.
- Svatos,Attygalle
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p. 1827 - 1836
(2007/10/03)
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- SYNTHESE STEREOSELECTIVE DE DIENES CONJUGUES A PARTIR D'ALCOOLS α-ALLENIQUES
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The reaction of a Grignard reagent with an α-allenic phosphate leads exclusively in every studied case to 1,3-dienes.A high stereoselectivity is observed for the formation of both double bonds; particularly, the organometallic species attacks preferentially in a trans direction from a group located on the terminal allenic carbon.In the case of the esters of secondary alcohols, it is more difficult to determine the factors which govern the stereochemistry of the other double bond.The Z configuration is then favoured in the reaction phosphate + RMgX but the E configuration is predominant in the reaction acetate + R2CuLi.
- Djahanbini, Dariouche,Cazes, Bernard,Gore, Jacques
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p. 3645 - 3656
(2007/10/02)
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