- Preparation method of L-carnitine
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The invention relates to the technical field of organic synthesis, in particular to a preparation method of L-carnitine, which comprises the following steps: by taking R-4-chloro-3-hydroxybutyrate as a raw material, carrying out catalytic cyclization under an alkaline condition to generate (2R)-2-ethylene oxide ethyl acetate, and carrying out ring-opening reaction with trimethylamine to obtain the L-carnitine. According to the invention, the technical scheme of first cyclization and then ring opening is adopted, so that the step of removing halide ions in ion exchange resin is avoided, byproducts such as sodium chloride and the like are convenient to remove, and the production cost is reduced; the method is simple to operate, low in production cost, high in target product purity, high in yield and suitable for being applied to industrial production.
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Paragraph 0034-0037; 0046-0047
(2021/12/07)
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- A Concise Stereoselective Total Synthesis of Methoxyl Citreochlorols and Their Structural Revisions
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A concise, stereoselective and protecting group free approaches for the total synthesis of (?)-(2S,4R)- and (+)-(2R,4S)-3′-methoxyl citreochlorols and their stereoisomers are demonstrated. All four stereoisomers were synthesized to establish the absolute stereochemistry of the reported structures and the structures were revised accordingly. The approach involves chelation controlled regioselective reduction of a diester, silyl iodide promoted ring-opening iodo esterification of lactones, highly chemo- and regioselective ring-opening of an epoxy ester, dichloromethylation of a carboxyl group, and syn- and anti-selective reduction of the resulted β-hydroxy ketone as key steps.
- Sunnapu, Ranganayakulu,Rajendar, Goreti
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p. 1637 - 1642
(2021/03/15)
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- Biocatalytic and Structural Properties of a Highly Engineered Halohydrin Dehalogenase
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Two highly engineered halohydrin dehalogenase variants were characterized in terms of their performance in dehalogenation and epoxide cyanolysis reactions. Both enzyme variants outperformed the wild-type enzyme in the cyanolysis of ethyl (S)-3,4-epoxybutyrate, a conversion yielding ethyl (R)-4-cyano-3-hydroxybutyrate, an important chiral building block for statin synthesis. One of the enzyme variants, HheC2360, displayed catalytic rates for this cyanolysis reaction enhanced up to tenfold. Furthermore, the enantioselectivity of this variant was the opposite of that of the wild-type enzyme, both for dehalogenation and for cyanolysis reactions. The 37-fold mutant HheC2360 showed an increase in thermal stability of 8°C relative to the wild-type enzyme. Crystal structures of this enzyme were elucidated with chloride and ethyl (S)-3,4-epoxybutyrate or with ethyl (R)-4-cyano-3-hydroxybutyrate bound in the active site. The observed increase in temperature stability was explained in terms of a substantial increase in buried surface area relative to the wild-type HheC, together with enhanced interfacial interactions between the subunits that form the tetramer. The structures also revealed that the substrate binding pocket was modified both by substitutions and by backbone movements in loops surrounding the active site. The observed changes in the mutant structures are partly governed by coupled mutations, some of which are necessary to remove steric clashes or to allow backbone movements to occur. The importance of interactions between substitutions suggests that efficient directed evolution strategies should allow for compensating and synergistic mutations during library design.
- Schallmey, Marcus,Floor, Robert J.,Hauer, Bernhard,Breuer, Michael,Jekel, Peter A.,Wijma, Hein J.,Dijkstra, Bauke W.,Janssen, Dick B.
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p. 870 - 881
(2013/07/25)
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- NEW CHIRAL SALEN CATALYSTS AND METHODS FOR THE PREPARATION OF CHIRAL COMPOUNDS FROM RACEMIC EPOXIDES BY USING THEM
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The present invention relates to new chiral salen catalysts and the preparation method of chiral compounds from racemic epoxides using the same. More specifically, it relates to new chiral salen catalysts that have high catalytic activity due to new molecular structures and have no or little racemization of the generated target chiral compounds even after the reaction is completed and can be also reused without catalyst regeneration treatment, and its economical preparation method to mass manufacture chiral compounds of high optical purity, which can be used as raw materials for chiral food additives, chiral drugs, or chiral crop protection agents, etc., using the new chiral salen catalysts.
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Page/Page column 39; 40
(2009/01/24)
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- Lobatamide C: Total synthesis, stereochemical assignment, preparation of simplified analogues, and V-ATPase inhibition studies
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The total synthesis and stereochemical assignment of the potent antitumor macrolide lobatamide C, as well as synthesis of simplified lobatamide analogues, is reported. Cu(I)-mediated enamide formation methodology has been developed to prepare the highly unsaturated enamide side chain of the natural product and analogues. A key fragment coupling employs base-mediated esterification of a β-hydroxy acid and a salicylate cyanomethyl ester. Three additional stereoisomers of lobatamide C have been prepared using related synthetic routes. The stereochemistry at C8, C11, and C15 of lobatamide C was assigned by comparison of stereoisomers and X-ray analysis of a crystalline derivative. Synthetic lobatamide C, stereoisomers, and simplified analogues have been evaluated for inhibition of bovine chromaffin granule membrane V-ATPase. The salicylate phenol, enamide NH, and ortho-substitution of the salicylate ester have been shown to be important for V-ATPase inhibitory activity.
- Shen, Ruichao,Lin, Cheng Ting,Bowman, Emma Jean,Bowman, Barry J.,Porco Jr., John A.
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p. 7889 - 7901
(2007/10/03)
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- Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)CoIII complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols
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The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)CoIII complex 1·OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H2O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to ≥ 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H2O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (krel) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, krel values for the HKR exceed 50, and in several cases are well in excess of 200.
- Schaus, Scott E.,Brandes, Bridget D.,Larrow, Jay F.,Tokunaga, Makoto,Hansen, Karl B.,Gould, Alexandra E.,Furrow, Michael E.,Jacobsen, Eric N.
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p. 1307 - 1315
(2007/10/03)
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- Enantiomerically pure β,γ-epoxyesters from β-hydroxylactones: Synthesis of β-hydroxyesters and (-)-GABOB
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The preparation of enantiomerically pure β,γ-epoxyesters was achieved by chemoselective opening of β-hydroxybutanolides with trimethylsilyliodide followed by cyclisation of the resulting iodohydrins with silver oxide. The reaction of these epoxyesters with lithio or magnesiocuprates afforded stereochemically pure α-substituted β-hydroxyesters. Alternatively, (-)-GABOB was synthesized in optically pure form from the iodohydrin 2′a.
- Larcheveque,Henrot
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p. 4277 - 4282
(2007/10/02)
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- PREPARATION DE NOUVEAUX SYNTHONS CHIRAUX: LES β,γ-EPOXYESTERS; APPLICATION A LA SYNTHESE DE β-HYDROXYESTERS ENANTIOMERIQUEMENT PURS
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The preparation of optically pure β,γ-epoxyesters 3 has been achieved through the opening of 3-hydroxybutanolides with trimethylsilyliodide followed by cyclisation with silver oxyde.They react with organocuprates to afford β-hydroxyesters of high enantiomerical purity.
- Larcheveque, Marc,Henrot, Serge
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p. 1781 - 1782
(2007/10/02)
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