- Synthesis of (R)-1,3-butanediol by enantioselective oxidation using whole recombinant Escherichia coli cells expressing (S)-specific secondary alcohol dehydrogenase
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The synthesis of (R)-1,3-butanediol (BDO) from its racemate was studied using whole cells of recombinant Escherichia coli expressing an (S)-specific secondary alcohol dehydrogenase (CpSADH) from Candida parapsilosis by enantioselective oxidation. Under the optimized conditions, the yield of (R)-1,3-BDO reached 72.6 g/l, with a molar recovery yield of 48.4% from a racemate of 15% and an optical purity of 95% ee.
- Yamamoto, Hiroaki,Matsuyama, Akinobu,Kobayashi, Yoshinori
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- The Absolute Configuration of 4-(Trichloromethyl)oxetan-2-one; A Case of Double Anchimeric Assistance with Inversion
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It has been shown that the absolute configuration of the oxetan-2-one (1) is opposite to that of its hydrolysis product, S-(-)-malic acid (3).
- Wynberg, Hans,Staring, Emiel G. J.
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- Diastereoselective route to (2R,5S)- and (2S,5S)-2-methyl-1,6-dioxaspiro[4.5]decane, a pheromone component of the wasp Paravespula vulgaris
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A diastereoselective approach to (2R,5S)- and (2S,5S)-2-methyl-1,6-dioxaspiro[4.5]decane 1 and 1a is described. The route starts with an alkylation reaction among the cyclopentanone N,N-dimethylhydrazone 6 and the chiral iodides (R)-3 or (S)-3, derived from the enantiomers of ethyl β-hydroxybutyrate, controlling the estereocenter at C-2 of the molecules. The alkylated products 7 and 7a were easily transformed into the 1,8-O-TBS-1,8-dihydroxy-5-nonanones 9 and 9a in four steps, and a subsequent stereoselective spiroketalization, in acidic media, afforded a Z:E mixture (1:2) of compounds 1 and 1a.
- Zarbin, Paulo H. G.,De Oliveira, Alfredo R. M.,Delay, Carlos E.
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- Preparation of enantiomerically pure 1,3-butanediol from threonine
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Enantiomerically pure R or S 1,3-butanediols were prepared in four steps from L to D threonine by nitrous deamination in the presence of bromide ion followed by esterification and reduction.
- Larcheveque,Mambu,Petit
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- Efficient synthesis of the ketone body ester (R)-3-hydroxybutyryl-(R)-3-hydroxybutyrate and its (S,S) enantiomer
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The ketone body ester (R)-3-hydroxybutyryl-(R)-3-hydroxybutyrate and its (S,S) enantiomer were prepared in a short, operationally simple synthetic sequence from racemic β-butyrolactone. Enantioselective hydrolysis of β-butyrolactone with immobilized Candida antarctica lipase-B (CAL-B) results in (R)-β-butyrolactone and (S)-β-hydroxybutyric acid, which are easily converted to (R) or (S)-ethyl-3-hydroxybutyrate and reduced to (R) or (S)-1,3 butanediol. Either enantiomer of ethyl-3-hydroxybutyrate and 1,3 butanediol are then coupled, again using CAL-B, to produce the ketone body ester product. This is an efficient, scalable, atom-economic, chromatography-free, and low cost synthetic method to produce the ketone body esters.
- Budin, Noah,Higgins, Erin,DiBernardo, Anthony,Raab, Cassidy,Li, Chun,Ulrich, Scott
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- Cloning and expression in Escherichia coli of a gene coding for a secondary alcohol dehydrogenase from Candida parapsilosis
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A gene encoding a stereo-specific secondary alcohol dehydrogenase (CpSADH) that catalyzed the oxidation of (S)-1,3-BDO to 4-hydroxy-2-butanone was cloned from Candida parapsilosis. This CpSADH-gene consisted of 1,009 nucleotides coding for a protein with M, 35,964. A recombinant Escherichia coli JM109 strain harboring the expression plasmid, pKK-CPA1, produced (R)-1,3-BDO (93.5% ee, 94.7% yield) from the racemate without any additive to regenerate NAD+ from NADH.
- Yamamoto, Hiroaki,Kawada, Naoki,Matsuyama, Akinobu,Kobayashi, Yoshinori
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- Enantioselective Production of (S)-3-Hydroxybutyric Acid, (S)-1,3-Butanediol and (R)-1,3-Butanediol Using Methanol Yeast
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(S)-3-Hydroxybutyric acid and (S)-1,3-butanediol were obtained by the treatment of 1,3-butanediol with the resting cells of methanol yeast, Candida boidinii (IFO 10574). (R)-1,3-Butanediol was also obtained in high optical purity by the enantioselective reduction of 4-hydroxy-2-butanone in the presence of methanol using the same methanol yeast.
- Matsumura, Shuichi,Imafuku, Hiroshi,Takahashi, Yoshinori,Toshima, Kazunobu
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- The Enantioface-differentiating Hydrogenation of the C=O Double Bond with Asymmetrically Modified Raney Nickel.XXXIII.The Preparation of (R)-and (S)-1,3-Butanediol from 4-Hydroxy-2-butanone
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The enantioface-differentianing hydrogenation of 4-hydroxy-2-butanone (I) to 1,3-butanediol (II) was conduced with asymmetrically modified metal catalysts.Among the modified catalysts examined, Raney nickel modified with a solution containing tartaric acid and NaBr (TA-NaBr-MRNi) gave the best results with respect to the optical and chemical yields. (R)-II, an optical purity of 69 percent was obtained in a quantitative chemical yeld by the use of (R,R)-TA-NaBr-MRNi. (S)-II was also obtained by the use of (S,S)-TA-NaBr-MRNi.A simple method for the preparation of optically pure (S)- and (R)-II from the hydrogenation product was also developed.
- Murakami, Shigeki,Harada, Tadao,Tai, Akira
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- SYNTHESIS OF 3-HYDROXYBUTYRYL 3-HYDROXYBUTYRATE AND RELATED COMPOUNDS
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In various embodiments methods of preparing hydroxybutyryl 3-hydroxybutyrate and related compounds are provided along with methods of use thereof.
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Paragraph 0308; 0317
(2021/04/02)
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- Conformational Dynamics-Guided Loop Engineering of an Alcohol Dehydrogenase: Capture, Turnover and Enantioselective Transformation of Difficult-to-Reduce Ketones
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Directed evolution of enzymes for the asymmetric reduction of prochiral ketones to produce enantio-pure secondary alcohols is particularly attractive in organic synthesis. Loops located at the active pocket of enzymes often participate in conformational changes required to fine-tune residues for substrate binding and catalysis. It is therefore of great interest to control the substrate specificity and stereochemistry of enzymatic reactions by manipulating the conformational dynamics. Herein, a secondary alcohol dehydrogenase was chosen to enantioselectively catalyze the transformation of difficult-to-reduce bulky ketones, which are not accepted by the wildtype enzyme. Guided by previous work and particularly by structural analysis and molecular dynamics (MD) simulations, two key residues alanine 85 (A85) and isoleucine 86 (I86) situated at the binding pocket were thought to increase the fluctuation of a loop region, thereby yielding a larger volume of the binding pocket to accommodate bulky substrates. Subsequently, site-directed saturation mutagenesis was performed at the two sites. The best mutant, where residue alanine 85 was mutated to glycine and isoleucine 86 to leucine (A85G/I86L), can efficiently reduce bulky ketones to the corresponding pharmaceutically interesting alcohols with high enantioselectivities (～99% ee). Taken together, this study demonstrates that introducing appropriate mutations at key residues can induce a higher flexibility of the active site loop, resulting in the improvement of substrate specificity and enantioselectivity. (Figure presented.).
- Liu, Beibei,Qu, Ge,Li, Jun-Kuan,Fan, Wenchao,Ma, Jun-An,Xu, Yan,Nie, Yao,Sun, Zhoutong
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p. 3182 - 3190
(2019/05/15)
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- Enantioselective hydrogenation of ketones over a tartaric acid-modified raney nickel catalyst: Substrate-modifier interaction strength and enantioselectivity
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Chiral (R,R)-tartaric acid and NaBr-doubly modified Raney nickel (TA-MRNi) is a promising heterogeneous catalyst for enantioselective hydrogenation of prochiral β-keto esters. To obtain deeper insights into the factors ruling the enantioselectivity, enantiodifferentiating hydrogenation of substituted ketones was studied over TA-MRNi and NaBr-modified RNi by use of combined individual-competitive hydrogenation techniques. Relative equilibrium adsorption constants of the substrates were estimated to evaluate their relative interaction strength with adsorbed tartaric acid moiety. DFT calculations were also performed to estimate the interaction energy through hydrogen bonding, providing clear support to the kinetic analysis and surface model. It is concluded with the enantioselective hydrogenation of ketones over TA-MRNi that the enantioselectivity increases as the substrate-modifier interaction strength increases: Methyl acetoacetate (MAA) > acetylacetone (AA) ～ 4-hydroxy-2-butanone (HB) > 2-octanone (2O).
- Choliq, Azka Azkiya,Murakami, Eitaro,Yamamoto, Shota,Misaki, Tomonori,Fujita, Morifumi,Okamoto, Yasuaki,Sugimura, Takashi
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p. 1325 - 1332
(2018/09/21)
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- Regio- and Enantioselective Sequential Dehalogenation of rac-1,3-Dibromobutane by Haloalkane Dehalogenase LinB
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The hydrolytic dehalogenation of rac-1,3-dibromobutane catalyzed by the haloalkane dehalogenase LinB from Sphingobium japonicum UT26 proceeds in a sequential fashion: initial formation of intermediate haloalcohols followed by a second hydrolytic step to produce the final diol. Detailed investigation of the course of the reaction revealed favored nucleophilic displacement of the sec-halogen in the first hydrolytic event with pronounced R enantioselectivity. The second hydrolysis step proceeded with a regioselectivity switch at the primary position, with preference for the S enantiomer. Because of complex competition between all eight possible reactions, intermediate haloalcohols formed with moderate to good ee ((S)-4-bromobutan-2-ol: up to 87 %). Similarly, (S)-butane-1,3-diol was formed at a maximum ee of 35 % before full hydrolysis furnished the racemic diol product.
- Gross, Johannes,Faber, Kurt,Hall, Mélanie,Prokop, Zbyněk,Janssen, Dick
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p. 1437 - 1441
(2016/12/24)
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- Asymmetric syntheses of the sex pheromones of pine sawflies, their homologs and stereoisomers
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We describe efficient and flexible enantioselective syntheses of the active enantiomers of the pheromones of pine sawflies, including the species Diprion jingyuanensis, their homologs and, stereoisomers, as well as those identified from the Chinese species Diprion jingyuanensis, i.e., 126. A total of 48 compounds, including acetates 78-101 and propanoates 102-125, have been synthesized. Our general approach towards these compounds originated from the commercially available chirons diethyl (S)- and (R)-malates, as well as ethyl (R)-3-hydroxybutanoate. The Seebach asymmetric methylation was employed in a key step to control additional configuration. Copyright
- Zheng, Jian-Feng,Lan, Hong-Qiao,Yang, Rui-Feng,Peng, Qi-Long,Xiao, Zhen-Hua,Tuo, Shi-Chuan,Hu, Kong-Zhen,Xiang, Yong-Gang,Wei, Zhen,Huang, Pei-Qiang,Zhang, Zhen
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p. 1799 - 1808,10
(2012/12/12)
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- A homogeneous catalyst for reduction of optically active esters to the corresponding chiral alcohols without loss of optical purities
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A ruthenium complex was found to catalyze the hydrogen reduction of esters under mild and neutral conditions. A variety of optically active esters can be reduced to the corresponding alcohols in excellent yield without loss of their optical purity or causing undesirable side reactions. Hydrogen reduction needs such simple operations - reaction, concentration, and purification - that the violent quench step and extraction step, which accompany conventional sodium borohydride or lithium aluminum hydride reduction, can be omitted.
- Kuriyama, Wataru,Ino, Yasunori,Ogata, Osamu,Sayo, Noboru,Saito, Takao
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supporting information; experimental part
p. 92 - 96
(2010/06/17)
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- Asymmetric, catalytic, and direct self-aldol reaction of acetaldehyde catalyzed by diarylprolinol
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(Chemical Equation Presented) An asymmetric, catalytic, and direct self-aldol reaction of acetaldehyde was catalyzed by diarylprolinol in NMP, affording the trimer acetal, which was generated by the reaction of the self-aldol product with another acetaldehyde molecule in a moderate yield with good enantioselectivity. Acetal is the synthetic equivalent of the self-aldol product, which can be converted into other synthetically useful compounds in one pot without compromising the enantioselectivity.
- Hayashi, Yujiro,Samanta, Sampak,Itoh, Takahiko,Ishikawa, Hayato
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supporting information; scheme or table
p. 5581 - 5583
(2009/07/11)
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- Ruthenium complexes of phosphine-aminophosphine ligands
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Ruthenium complexes of phosphinoferrocenylaminophosphine ligands (BoPhoz ligands) have been prepared by combining the ligands with tris(triphenylphosphine)ruthenium dichloride and precipitating the complexes. The optimal species exhibit high enantioselectivities for the asymmetric hydrogenation of functionalized ketones, particularly β-ketoesters.
- Boaz, Neil W.,Ponasik Jr., James A.,Large, Shannon E.
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p. 4033 - 4035
(2007/10/03)
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- A concise asymmetric synthesis of (2S,3S,7S)-3,7-dimethylpentadecan-2-yl acetate and propionate, the sex pheromones of pine sawflies
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(2S,3S,7S)-3,7-Dimethylpentadecan-2-yl acetate (2) and its propionate analogue (3) are the main sex pheromones of all Neodiprion species and Diprion similes, respectively. Starting from (S)-malic acid and employing a highly chemo-, regio-, and stereoselective tandem ester reduction-epoxide formation-reductive epoxide-opening reaction protocol, an efficient total synthesis of (2S,3S,7S)-2 and -3 is reported herein.
- Huang, Pei-Qiang,Lan, Hong-Qiao,Zheng, Xiao,Ruan, Yuan-Ping
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p. 3964 - 3967
(2007/10/03)
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- Synthesis of chiral β3-aminoxy peptides
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A series of chiral β3-aminoxy acids or amides with various side chains have been synthesized via two different approaches. One is the Arndt-Eistert homologation approach, using chiral α-aminoxy acids as starting materials. The other approach, utilizing the enantioselective reduction of β-keto esters catalyzed by baker's yeast or chiral Ru(II) complexes, produces chiral β3-aminoxy acids with nonproteinaceous side chains. The oligomers of β3-aminoxy acids can be readily prepared using EDCI/HOAt as the coupling reagent.
- Yang, Dan,Zhang, Yu-Hui,Li, Bing,Zhang, Dan-Wei
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p. 7577 - 7581
(2007/10/03)
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- Catalytic Hydrogenation of Chiral α-Amino and α-Hydroxy Esters at Room Temperature with Nishimura Catalyst without Racemization
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The hydrogenation of carboxylic acid derivatives at room temperature was investigated. With a mixed Rh/Pt oxide (Nishimura catalyst), low to medium activity was observed for various α-amino and α-hydroxy esters. At 100 bar hydrogen pressure and 10% catalysts loading, high yields of the desired amino alcohols and diols were obtained without racemization. The most suitable α-substituents were NH2, NHR, and OH, whereas β-NH2 were less effective. Usually, aromatic rings were also hydrogenated, but with the free bases of amino acids as substrates, some selectivity was observed. No reaction was found for α-NR2, α-OR, and unfunctionalized esters; acids and amides were also not reduced under these conditions. A working hypothesis for the mode of action of the catalyst is presented.
- Studer, Martin,Burkhardt, Stefan,Blaser, Hans-Ulrich
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p. 802 - 808
(2007/10/03)
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- Absolute stereochemistry of amphidinolide C.
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[structure in text] The absolute configurations at 12 chiral centers in amphidinolide C (1), a potent cytotoxic 25-membered macrolide isolated from a marine dinoflagellate Amphidinium sp., were determined to be 3S, 4R, 6R, 7R, 8R, 12R, 13S, 16S, 20R, 23R, 24R, and 29S by combination of NMR analyses, degradation experiments, and synthesis of the C-1-C-7 segment.
- Kubota,Tsuda,Kobayashi
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p. 1363 - 1366
(2007/10/03)
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- The bakers' yeast reductions of α- and β-keto ester derivatives in the presence of a sulfur compound
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Improvement of the enantioselectivity and enhancement of the reactivity were achieved in the bakers' yeast reduction of the α- and β-keto ester derivatives by the addition of a sulfur compound. High enantioselectivity in the bakers' yeast reduction of keto esters was accomplished by using combination of an addition of a sulfur compound with an appropriate selection of the alcohol part of the ester.
- Hayakawa, Ryuuichirou,Nozawa, Kazumi,Kimura, Kimihiko,Shimizu, Makoto
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p. 7519 - 7528
(2007/10/03)
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- A general synthesis of homochiral β-hydroxy N-acetylcysteamine thioesters
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A convenient and efficient route for the enantioselective synthesis of functionalised β-hydroxy N-acetylcysteamine thioesters is described. The route allows the facile incorporation of vicinal 13C labelling to produce intermediates required for biosynthetic studies on a wide range of polyketide metabolites, e.g. 6-MSA, monocerin, colletodiol and strobilurins.
- Le Sann, Christine,Simpson, Thomas J.,Smith, David I.,Watts, Paul,Willis, Christine L.
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p. 4093 - 4096
(2007/10/03)
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- Stereoselective chemoenzymatic synthesis of both enantiomers of protected 4-amino-2-pentanone
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An acetal protected 4-amino-2-pentanone was synthesised by two different routes in 10 and seven steps, respectively, the key step being a microbiological reduction. Both enantiomers of the amine were obtained enantiomerically pure.
- Besse, Pascale,Ciblat, Stephane,Canet, Jean-Louis,Troin, Yves,Veschambre, Henri
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p. 2213 - 2224
(2007/10/03)
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- Efficient general synthesis of 1,2- and 1,3-Diols in high enantiomeric excess via the intramolecular asymmetric reduction of the corresponding ketoalkyl diisopinocampheylborinate intermediates
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The first successful asymmetric reduction of unhindered aliphatic ketones with B-chlorodiisopinocampheylborane is reported. In contrast to the reduction in high ee of aralkyl ketones, such as acetophenone, with the reagent, the reduction of unhindered dialkyl ketones, such as 3-methyl-2-butanone, provides only poor ee. However, treatment of α- and β-hydroxyketones with one equiv of diisopnocampheylborane or B-chlorodiisopinocampheylborane rapidly produces the corresponding ketoalkyl diisopinocampheylborinate intermediates, which then undergo facile intramolecular reduction. This reaction sequence, followed by oxidative workup, provides a general synthesis of 1,2- and 1,3-diols in 84≤99% enantiomeric excess.
- Ramachandran, P. Veeraraghavan,Lu, Zhi-Hui,Brown, Herbert C.
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p. 761 - 764
(2007/10/03)
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- Substrate structure and incubation-parameter-dependent selectivities in chiral discrimination of galactopyranosides by β-galactosidase hydrolysis
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Mono-β-galactopyranosides of (+/-)-propane-1,2-diol, (+/-)-butane-1,3-diol, (+/-)-pentane-1,4-diol, (+/-)-butan-2-ol, (+/-)-pentan-2-ol and (+/-)-1,2-O-isopropylideneglycerol were synthesized by the Koenigs-Knorr reaction using hydroxycarbonyl compounds as precursors for the diolic substrates.Hydrolysis of 3-hydroxybutyl β-D-galactopyranoside 18 by β-galactosidases from Eschrichia coli, Aspergillus oryzae, Kluyveromyces lactis and Bacillus circulans, respectively, resulted in each case in an enantiomeric enrichment of the released diol.This was most significant with the E. coli enzyme and and increased with higher reaction temperature and shorter incubation periods.Under standartized conditions, cleavage of all synthesized galactopyranosides by this enzyme showed the highest stereoselectivity for butane-1,3-diol, butan-2-ol and isopropylideneglycerol with enantiomeric excesses in the range 60-75percent.For compounds with structural similarity to the natural substrate lactose, enhanced stereodiscriminations were expected.However, this could not be confirmed and instead a specific hydrophobic interaction is suggested to play a crucial role.
- Werschkun, Barbara,Koenig, Wilfried A.,Kren, Vladimir,Thiem, Joachim
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p. 2459 - 2466
(2007/10/02)
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- Asymmetric intramolecular hydrosilylation of hydroxyketones
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A procedure for the catalytic asymmetric intramolecular hydrosilylation of α- and β-hydroxyketones has been developed. A cationic rhodium (I) catalyst bearing the new chiral diphosphine (R,R)-i-Pr-DuPHOS affords the product diols in up to 93% ee.
- Burk, Mark J.,Feaster, John E.
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p. 2099 - 2102
(2007/10/02)
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- Stereoselective Acetalization of 1,3-Alkanediols by l-Menthone: Application to the Resolution of Racemic 1,3-Alkanediols and to the Determination of the Absolute Configuration of Enantiomeric 1,3-Alkanediols
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A general and reliable method for the resolution of racemic 1,3-alkanediols, which involves their conversion into diastereomeric spiroacetals derived from l-menthone, is described.Thus, the reaction of the bis-O-trimethylsilyl derivatives of racemic 1,3-alkanediols with l-menthone in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate affords the diastereomeric spiroacetals 3 and 4.The two can be readily separated by silica gel column chromatography.Hydrolysis of each diastereomer under acidic conditions liberates the corresponding enantiomerically pure diol.An empirically derived correlation of configuration and 1H NMR chemical shifts for spiroacetals 3 and 4 has been developed which is rationalized based on long-range effects due to the magnetic anisotropy inherent to the menthane ring in a rigid spiroacetal conformation.The method described here should be widely applicable to the determination of the absolute configuration of various 1,3-alkanediols.
- Harada, Toshiro,Kurokawa, Hideaki,Kagamihara, Yasuhiro,Tanaka, Sachi,Inoue, Atsushi,Oku, Akira
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p. 1412 - 1421
(2007/10/02)
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- An efficient synthesis of enantiomerically pure (R)-(2-benzyloxyethyl)oxirane from (S)-aspartic acid
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A 3-step synthesis of the title compound from (S)-aspartic acid is described. The overall yield of this process is 65% and the enantiomeric purity (ep) of the product is greater than 99%.
- Frick,Klassen,Bathe,Abramson,Rapoport
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p. 621 - 623
(2007/10/02)
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- Asymmetric hydrogenation of prochiral carboxylic acids and functionalized carbonyl compounds catalysed by ruthenium(II)-binap complexes with aryl nitriles (binap=(R)- or (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl)
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Complexes RuCl2(ArCN)2(binap), II (binap=(R)- or (S)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl; ArCN=benzonitrile, a; 2-furancarbonitrile, b; pentafluorobenzonitrile, c) were prepared, and their solution properties were investigated by 31P NMR measurements.The catalytic aactivities and enantioselectivities for IIa-c catalysed hydrogenation of some prochiral acids were very similar to those provided by Ru2Cl4(binap)2(NEt3), I.In the hydrogenation of β-functionalized carbonyl compounds, however, IIa-c showed considerably lower activities and/or selectivities, compared with complex I.The differences in IIa-c catalysed reactions are discussed in relation to the coordinating abilities of ArCN in II.
- Shao, Liming,Takeuchi, Kasumi,Ikemoto, Makoto,Kawai, Toshiyasu,Ogasawara, Masamichi,et al.
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p. 133 - 147
(2007/10/02)
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- Chiral α,ω-Dioxy-Carbanions from 1,3-Propanediol and 1,4-Butanediol by Sparteine-Assisted Deprotonation. Enantioselective Synthesis of 1,3- and 1,4-Diols, (R)-Pantolactone, and a Cyclopropane
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Prostereogenic mono- and dicarbamates of 1,3-propanediol and 1,4-butanediol are deprotonated by the sec-butyllithium/(-)-sparteine system with high enantiotopic differentiation.The electrophilic substitution of the intermediate chiral carbanions furnishes the title compounds with >95percent ee. Key words: Chiral 1-oxy-carbanions; enantioselective deprotonation; (-)-sparteine.
- Paetow, Mario,Ahrens, Hartmut,Hoppe, Dieter
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p. 5323 - 5326
(2007/10/02)
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- Synthesis of two stereoisomers of the propanoate ester of 8-methyl-2-decanol using remote asymmetric induction
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A stereoselective synthesis of two isomers (2S,8R) and (2S,8S) of 8-methyl-2-decanol opanoate (the pheromone emitted by females of several Diabrotica species) has been accomplished using mote stereochemical relationships between carbons 3 and 9 of the 3,9-dimethyl decanolides 14 and 16.
- Ferrelra, J. Tercio B.,Simonelli, Fabio
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p. 6311 - 6318
(2007/10/02)
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- RESOLUTION OF 1,3-ALKANEDIOLS VIA CHIRAL SPIROKETALS DERIVED FROM l-MENTHONE
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Ketalization reaction of racemic 1,3-alkanediols with l-menthone gave a mixture of diastereomeric spiroketals that was easily separated by silica gel column chromatography and converted into enantiomerically pure diols by acid-catalyzed hydrolysis.
- Harada, Toshiro,Kurokawa, Hideaki,Oku, Akira
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p. 4843 - 4846
(2007/10/02)
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- 3-Hydroxyglutarate and β,γ-Epoxy Esters as Substrates for Pig Liver Esterase (PLE) and α-Chymotrypsin
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The pH dependence of the α-chymotrypsin-catalyzed hydrolysis of dimethyl 3-hydroxyglutarate (3) has been studied.The e.e. was determined by HPLC analysis of diastereoisomeric camphanoic-acid derivatives.Kinetic resolution of the β,γ-epoxy esters 10 and 24 by pig liver esterase has been shown to provide an alternative access to chiral β-hydroxy esters and acids of high optical purity.By this latter method, the unnatural enantiomer of γ-amino-β-hydroxybutyric acid (GABOB) has been sinthesized.Finally, dimethyl meso-3,4-epoxyadipate (19) was hydrolyzed by pig liver esterase with almost 100 percent selectivity.
- Mohr, Peter,Roesslein, Lukas,Tamm, Christoph
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p. 142 - 152
(2007/10/02)
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- A SYNTHESIS OF (S,S)-(+)-GRAHAMIMYCIN A1
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The preparation of (S)-1-(1,3-dithian-2-yl)-2-hydroxypropane 3 and its transformation into (S,S)-(+)-grahamimycin A1, through intramolecular pinacolic coupling of dialdehyde 9, are described.
- Ghiringhelli, Dario
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p. 287 - 290
(2007/10/02)
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- Stereochemistry of Friedel-Crafts Reaction of Benzene with Optically Active 2-Methyloxetane
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The Friedel-Crafts alkylation of benzene with (+)-2-methyloxetane in the presence of Lewis acids (AlCl3, SnCl4, and TiCl4) gave 3-phenyl-1-butanol with 20-60percent inversion of configuration at the reaction center and a mixture of 4-chloro-2-butanol and 3-chloro-1-butanol in optically active form as the by-products. These by-products were formed by the attack of the chlorine atom in Lewis acid. The stereochemical course of the reaction to 3-chloro-1-butanol varied with the kind of catalyst, i.e., inversion with AlCl3 or TiCl4 and retention with SnCl4. The addition of nitromethane to the reaction system promoted the retentive ring-opening to 3-chloro-1-butanol.
- Segi, Masahito,Takebe, Masaki,Masuda, Shinji,Nakajima, Tadashi,Suga, Sohei
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p. 167 - 170
(2007/10/02)
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- Access to (S)-2-Methyloxetane and the Precursor (S)-1,3-Butanediol of Hight Enantiomeric Purity
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(S)-2-Methyloxetane (1) and its precursor (S)-1,3-butanediol (2) were prepared in low to moderate chemical yield with less than 0.5percent racemization from (S)-ethyl lactate (4) and from (2S,3S)-allothreonine (14b).For the first time the enantiomeric purities of both the starting material and the product (1) were carefully determined by high-precision capillary gas chromatography on optically active resolving stationary phases.The validity of the quadrant rule, correlating the relative configuration of alkyloxiranes with the order of elution from manganese(II) bis (3) by complexation gas chromatography, is also confirmed for 2-methyloxetane (1).
- Hintzer, Klaus,Koppenhoefer, Bernhard,Schurig, Volker
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p. 3850 - 3854
(2007/10/02)
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