Influence of substituents on enantiomeric ratio in transesterification of racemic C-3 synthons using lipase B from Candida antarctica

The fluorides, chlorides and bromides of 3-halo-1-phenoxy-2-propanol, 3-halo-1-phenylmethoxy-2-propanol and 3-halo-1-(2-phenylethoxy)-2-propanol have been resolved by transesterification with various butanoates as acyl donors in hexane and lipase B from Candida antarctica (Novozyme 435) as catalyst. The enantiomeric ratio E depended on the hydroxy protecting groups in 1-position and the halogens in 3-position. For some substrates, the enantiomeric ratio was dependent on the acylating agent.     

Purification and Characterization of a DNA Topoisomerase I from Bifidobacterium breve

The monoacylation of (η⁶-1,2-benzenedimethanol)tricarbonylchromium (2) by vinyl acetate, palmitate and benzoate, alcoholysis of the corresponding diesters of 2 in n-butanol, and acylation of (η⁶-benzyl alcohol) tricarbonylchromium by (±)-vinyl 2-phenoxypropanoate and 2-phenylpropanoate were accomplished with lipase P (from P. fluorescens) and lipase CC (from C. cylindracea) to give optically active organometallic esters. Their configurations indicated that the stereoselectivity of each of these two lipases was in marked contrast. An active site model for them is proposed.     

Asymmetric Hydrolysis of Racemic 2-Oxazolidinone Esters with Lipases

The enzymatic hydrolysis of (R, S)-5-acyloxymethyl-3-alkyl-oxazolidin-2-one I and the behavior of (S)-I for extraction with an organic solvent were examined so as to extend the biological resolution to racemates, and to learn about more appropriate combinations of substrates with lipases on the asymmetric hydrolysis. The combination of (R, S)-5-hexanoyloxymethyl-3-tert-butyl-oxazolidin-2-one 4 with lipoprotein lipase Amano 3 (L. P. L. Amano 3, origin; Pseudomonas aeruginosa) and that of (R, S)-5-octanoyloxymethyl-3-isopropyl-oxazolidin-2-one 14 with L. P. L. Amano 3 efficiently gave (S)-5-hydroxymethyl-3-tert-butyl-oxazolidin-2-one (S)-lla (99% e.e.) and (S)-5-hydroxymethyl-3-isopropyl-oxazolidin-2-one (S)-IIb (99% e.e.),respectively. (S)-IIa and (S)-IIb could be considered to be favorable intermediates for preparing optically active β-blockers.     

Comparison of Soybean Tissue Extracted with Different Solvents

The enantioselective hydrolysis of (R,S)-3-acetoxymethyl-7,8-difluoro-2,3-dihydro-4H-[1,4]benzoxazine (I) with enzymes was investigated. Optically active I and its hydrolyzate, 7,8-difluoro-2,3-dihydro-3-hydroxymethyl-4H-[1,4]benzoxazine (II), are the intermediates for preparing optically active ofloxacins, whose racemate is known to be an excellent antibacterial agent. Lipoprotein lipase from Pseudomonas fluorescens (LPL Amano 3) was found to predominantly hydrolyze (S)-I, giving (R)-I in 54% e.e. and (R)-II in 44% e.e. On the other hand, lipase from Candida cylindracea was found to predominantly hydrolyze (R)-I, giving (S)-I in 24% e.e. and (S)-II in 20% e.e. Since, the optical purities of I and II thus obtained were not particularly high, these optically active I and II were converted into 3-acetoxymethyl-7,8-difluoro-2,3-dihydro-4-(3,5-dinitrobenzoyl)-4H-[1,4]benzoxazine (IV). After recrystallizing IV from ethyl acetate-hexane, (S)- and (R)-II were obtained with high enantiomeric excess by removing the crystallized racemic IV and subsequently hydrolyzing the resulting optically active IV with alkali. The reduction of II afforded 7,8-difluoro-2,3-dihydro-3-methyl-4H-[1,4]benzoxazine (III), for which the optical purity was estimated to be >96%e.e. by HPLC analysis. (R)- and (S)-ofloxacin were prepared from (R)- and (S)-III with retention of their configuration.     

Studies on enantioselective hydrolysis of the acetic ester of a secondary alcohol with Arthrobacter lipase

Summary Characteristics of the enantioselective hydrolysis of the acetic ester of 4-hydroxy-3-methyl-2-(2-propynyl)-2-cyclopentenone (HMPC) by Arthrobacter lipase were investigated in a water/oil biphasic reaction mixture. Kinetic studies revealed that the strict enantioselectivity was entirely due to a difference in the catalytic constants for the enantiomeric substrates and that (S)-HMPC acetate acted as a competitive inhibitor. The comparison of enantioselectivity for the acetates of HMPC analogues indicated that hydrophobic substituents in the HMPC molecule were essential for the strict enantioselectivity.Biological preparation of an optically active alcohol. Part II     

Enantioselective biocatalytic reactions on (±)-aryl alkyl ketones with native and modified porcine pancreatic lipase

Abstract

Porcine pancreatic lipase (PPL), pre-incubated with acetophenone in tetrahydrofuran, fails to recognize ortho- and para-acyloxy functions with respect to the nuclear carbonyl group in (±)-2,4-diacyloxyphenyl alkyl ketones and produces novel aryl alkyl ketones in moderate-to-highly optically active forms; this result supports the hypothesis on the mechanism of action of PPL in deacylation reactions on peracylated polyphenolics.     

First enantioselective hydrolysis of n-alkyl sec-alkyl carbonates by porcine pancreatic lipase

Summary n-Alkyl sec-alkyl carbonates were enantioselectively hydrolyzed by porcine pancreatic lipase to give optically active (R)-sec-alkanols. (R)-1-Phenylethanol with an optical purity of >99%ee was obtained by the resolving method.     

Relationship between Stereoisomerism and Biological Activity of Pyrethroids

(+)-trans-Homochrysanthemic acid, when boiled in dilute sulfuric acid, gives (+)-trans-ε-hydroxy-dihydrohomochrysanthemic acid, m.p. 176–7°, together with (+)-δ, δ-dimethyl-γ-isobutenyl-δ-valerolactone. The formation of optically active lactone from (+)-trans-homochrysanthemic acid provides another cogent evidence for the structure of the lactone previously deduced on the racemic compound.

The Arndt-Eistert reaction of the homo-acids give further higher homologues such as (±)-,(+)-trans-β-(3-isobutenyl-2, 2-dimethylcyclopropane-1)-propionic acids and (±)-cis-3-isobutenyl-2, 2 dimethylcyclobutane-1-acetic acid. Both trans-acids, in boiling dilute sulfuric acid, give the same (±)-γ-(1′, 1′, 4′-trimethyl-pent-2′-enyl)-butyrolactone together with the corresponding hydroxy-acids, optically inactive and active, respectively.

Complete resolution of (±)-trans-homochrysanthemic acid and (±)-trans-β-(3-isobutenyl-2, 2-dimethycyclopropane-1)-propionic acid was achieved by means of optically active α-phenylethylamine.     

Lactones 29. Enzymatic resolution of racemic γ-lactones

Studies on the application of commercially available enzymes to resolution of the racemic unsaturated γ-lactones: 5-(3-methylbutylidene)-4-methyl-tetrahydrofuran-2-one (1a) and 5-(3,3-dimethylbutylidene)-4-methyl-tetrahydrofuran-2-one (2a) are presented. Lipase PS, Rhizopus niveus lipase, Rhizopus arrhizus lipase, porcine pancreas lipase and hog liver esterase transformed substrates into their respective γ-keto acids with good efficiency (50–75%). Three of them hydrolysed the studied lactones with moderate enantioselectivity. Enantiomeric excesses determined by GC for the unreacted lactones were in the range of 20–60%. Lipase PS preferentially hydrolysed the (+) enantiomers of lactones 1a and 2a whereas R. niveus lipase hydrolysed the (?) enantiomers, respectively.     

Preparation of Optically Active 2-Aminobutanoic Acid via Optical Resolution by Replacing Crystallization

An attempt was made to use a simple procedure to obtain (R)- and (S)-2-aminobutanoic acids [(R)- and (S)-1] which are non-proteinogenic α-amino acids and are useful as chiral reagents in asymmetric syntheses. Compound (RS)-1 p-toluenesulfonate [(RS)-2], which is known to exist as a conglomerate, was optically resolved by replacing crystallization with (R)- and (S)-methionine p-toluenesulfonate [(R)- and (S)-3] as optically active co-solutes. When (S)-3 was employed as the co-solute, (R)-2 was preferentially crystallized from a supersaturated solution of (RS)-2 in 1-propanol, as was (S)-2 in the presence of (R)-3. (R)- and (S)-2 recrystallized from 1-propanol were treated with triethylamine in methanol to give (R)- and (S)-1 in optically pure forms.     

Preparation of an optically pure secondary alcohol of synthetic pyrethroids using microbial lipases

Summary Enzyme-catalysed hydrolysis of esters of 4-hydroxy-3-methyl-2-(2-propynyl)-cyclopent-2-enone (HMPC) was examined for the preparation of the optically pure alcohol moiety of synthetic pyrethroids. Among microorganisms and lipases tested, some bacterial lipases hydrolysed the ester of HMPC with high enantioselectivity and high reaction rate. Arthrobacter lipase gave the optically pure (R)-HMPC at 50% hydrolysis in a two-liquid phase reaction system of water and the insoluble substrate. The hydrolysis proceeded even at a substrate concentration of 80w/v%. The enantioselectivity was not changed with the chain length of the acid moiety of the esters. By combination of the enzymatic resolution with a chemical inversion of the (R)-alcohol, an efficient proess was developed for the total conversion of racemic HMPC to (S)-HMPC, which is an important alcohol for preparation of an insecticidallyactive synthetic pyrethroid.Biological preparation of an optically active alcohol. Part I     

Lipase stereoselectivity and regioselectivity toward three isomers of dicaprin: A kinetic study by the monomolecular film technique

Here we present a kinetic study on the steroselectivity and regioselectivity of 23 purified lipases of animal and microbial origin. This work, concerning a general problem of the mechanism of lipase–substrate molecular recognition, was performed using pure dicaprin isomers: 1,2-sn-dicaprin, 2,3-sn-dicaprin, and 1,3-sn-dicaprin spread as monomolecular films at the air–water interface. The first two isomers are optically active antipodes (enantiomers), forming stable films up to 40 mN m^?1, while the last is a prochiral compound, with a surface pressure of collapse of 32 mN m^?1. To our knowledge, this is the first report on the use of three diglyceride isomers as lipase substrates under identical and controlled physicochemical conditions. The lipases tested display a typical behaviour, characteristic of each enzyme, which allowed us to classify the lipases in groups according to (1) the profiles of enzyme velocity as a function of surface pressure, (2) their preferences for a given diglyceride isomer, quantified using new parameters termed steroselectivity index (S.I.), vicinity index (V.I.), and surface pressure threshold (S.P.T.). The general observation, true for all the enzymes tested, is that the three substrates are well differentiated, and the differentiation is more pronounced at high interfacial energy (low surface pressure). This observation supports our hypothesis that lipase conformational changes, resulting from the enzymesurface interaction, affect the enzymes' specificities. Generally speaking, the stereopreference for either sn-1 or sn-3 position on glycerides is maintained both in the case of di- and tri-glycerides. © 1995 Wiley-Liss, Inc.     

Preparation and isolation of 2-methylamino-3-phenylpropanoic acid enantiomers using selective crystallization

First, (RS)-2-chloro-3-phenylpropanoic acid [(RS)-CPP] was optically resolved using ethyl (S)-phenylalaninate as a resolving agent, aiming at preparation of optically active 2-methylamino-3-phenylpropanoic acid (MPP). The (R)-CPP obtained as the sodium salt monohydrate was reacted with methylamine to give (S)-2-methylamino-3-phenylpropanoic acid [(S)-MPP]. Next, the optical resolution of (RS)-MPP was also attempted via molecular compound formation with optically active mandelic acid (MAN). The molecular compound of (R)-MPP with (S)-MAN [(R)-MPP (S)-MAN] was obtained as the less soluble diastereomeric compound, while the (S)-MPP (S)-MAN compound was found to be the more soluble one. Recrystallization of (R)-MPP (S)-MAN compound from water, followed by treatment with acetone, gave optically pure (R)-MPP in 79% yield, based on a half amount of the starting (RS)-MPP. The (S)-MPP obtained from (S)-MPP (S)-MAN compound was again subjected to formation of molecular compound with (R)-MAN to give optically pure (S,)-MPP in 66% yield. Chirality 9:386–389, 1997. © 1997 Wiley-Liss, Inc.     

Stereoselective Synthesis of the Optically Active Samin Type of Lignan from L-Glutamic Acid

The optically active samin type of lignan, (1R,2S,5R, 6S)-6-(2-methoxy-4,5-methylenedioxyphenyl)-3,7-dioxabicyclo[3.3.0]octan-2-ol, was stereoselectively synthesized from L-glutamic acid via (2R,3R)-2-[(1S and R)- 1-[(tert-butyldimethylsilyl)oxy]-1-(2-methoxy-4,5-methylenedioxyphenyl)methyl]-3-[(tert-butyldiphenylsilyl)oxy]methyl-1,4-butanediol.     

Lipase-catalyzed diacylation of 1,3-butanediol

Summary A kinetic resolution of 1,3-butanediol was accomplished by lipase-catalyzed enantioselective diacylations in organic solvent. Diacylation of 1,3-butanediol was carried out using immobilized lipase SP382 (from Candida sp.) to produce (R) -1,3-diacetoxybutane with 85.8% e.e.. And then, this optically active product was chemically hydrolyzed to diol, and re-acylated with lipase SP382 to (R) -1,3-diacetoxybutane with over 98% e.e..     

Synthesis of Optically Active 1,4-Thiazane-3-carboxylic Acid via Optical Resolution by Preferential Crystallization of (RS)-2-Amino-3-[(2-chloroethyl)sulfanyl]propanoic Acid Hydrochloride

Optically active 1,4-thiazane-3-carboxylic acid [TCA] was synthesized from cysteine via optical resolution by preferential crystallization. The intermediate (RS)-2-amino-3-[(2-chloroethyl)sulfanyl]propanoic acid hydrochlo-ride [(RS)-ACS?HCl] was found to exist as a conglomerate based on its melting point, solubility and IR spectrum. (RS)-ACS?HCl was optically resolved by preferential crystallization to yield (R)- and (S)-ACS?HCl. (R)- and (S)-ACS?HCl thus obtained were recrystallized from a mixture of hydrochloric acid and 2-propanol, taking account of the solubility of (RS)-ACS?HCl, efficiently yielding both enantiomers in optically pure forms. (R)- and (S)-TCA were then respectively synthesized by the cyclization of (R)- and (S)-ACS?HCl in ethanol in the presence of triethylamine.     

Release,Regeneration and Mutant Induction of Pleurotus cornucopiae (‘Tamogitake’) Protoplasts

Both enantiomers of aliphatic and aromatic cyanohydrins were hydrolyzed with the aid of Rhodococcus butanica ATCC 21197 to afford optically active α-hydroxy acids. The usefulness of this reaction is demonstrated by the synthesis of optically pure (R)-4-dodecanolide, a defensive secretion of rove beetles, starting from (R)-2-hydroxydecanenitrile.     

Optimization of (R,S)-1-phenylethanol kinetic resolution over Candida antarctica lipase B in ionic liquids

The kinetic resolution of racemates constitutes one major route to manufacture optically pure compounds. The enzymatic kinetic resolution of (R,S)-1-phenylethanol over Candida antarctica lipase B (CALB) by using vinyl acetate as the acyl donor in the acylation reaction was chosen as model reaction. A systematic screening and optimization of the reaction parameters, such as enzyme, ionic liquid and substrates concentrations with respect to the final product concentration, were performed. The enantioselectivity of immobilized CALB commercial preparation, Novozym 435, was assayed in several ionic liquids as reaction media. In particular, three different ionic liquids: (i) 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆], (ii) 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF₄] and (iii) 1-ethyl-3-methylimidazolium triflimide [emim][NTf₂] were tested. At 6.6% (w/w) of Novozym 435, dispersed in 9.520 M of [bmim][PF₆] at 313.15 K, using an equimolar ratio of vinyl acetate/(R,S)-1-phenylethanol after 3 h of bioconversion, the highest possible conversion (50%) was reached with enantiomeric excess for substrate higher than 99%.     

Optical Rotatory Dispersion of Rotundifolone

Microbial (enzymatic) hydrolysis of (±)-O-acetyl allethrolone gave (?)-(R)-allethrolone with (+)-(S)-O-acetyl allethrolone. And microbial hydrolysis of (±)-cis and trans-2-allylcyclopentyl acetates gave the low optically active cis and trans-2-allylcyclopentanols with the acetates of their antipodes. Also, the acetates of (±)-primary alcohols with cyclopropane and cyclohexene rings: (±)-chrysanthemyl alcohol, α-cyclogeraniol, were hydrolyzed by microorganisms to give the optically active alcohols in low optical purities Further, synthesis and microbial resolution of racemic hydroxy-trimethylcyclohexanones, useful intermediate for synthesis of compounds related to carotenoids, were tried.     

Enantioselective reduction of acetyldimethylphenylsilane by Trigonopsis variabilis (DSM 70714)

Summary Growing and resting cells of the yeast Trigonopsis variabilis (DSM 70714) can be used for the enantioselective reduction of the organosilicon compound acetyldimethylphenylsilane (1) to give optically active (R)-(1-hydroxyethyl)dimethylphenylsilane [(R)-2] in good yields. The enantiomeric purity of the isolated product was determined to be 62–86% ee depending on the substrate concentration used. Both substrate and product caused an inhibition of the reaction at concentrations higher than 0.35 and 0.5 g/l, respectively. Besides, higher substrate and product concentrations led to increased formation of the by-product 1,1,3,3-tetramethyl-1,3-diphenyldisiloxane. Considering the limiting substrate and product concentrations, it was possible to use the same biomass at least 5 times without significant loss of enzyme activity. 3-Methyl-3-phenyl-2-butanone (5) and acetyldimethylphenylgermane (7), which represent carbon and germanium analogues of 1, were also found to be accepted as substrates by Trigonopsis variabilis (DSM 70714). The reduction rates of the silicon (1) and germanium compound (7) were much higher than the transformation rate of the corresponding carbon analogue 5.