1,720,987 research outputs found
Production of geranyl acetate and other acetates by direct esterification catalyzed by mycelium of Rhizopus delemar in organic solvent
No full textDry mycelium of Rhizopus delemar MIM catalyzed the formation of geranyl acetate using 110 mM geraniol and acetic acid at 55°C in heptane to give 11.9 g/l (55% molar conversion). Geranyl acetate was produced at 72.5-75 g/l after 10 days by semi-continuous addition of the substrates. Rhizopus delemar also catalyzed the direct acetylation of different primary alcohols with molar conversions ranging from 65 to 98%
Enantioselective oxidation of prochiral 2-methyl-1,3-propandiol by Acetobacter pasteurianus
No full textThe microbial oxidation of prochiral 2-methyl-1,3-propandiol into (R)-3-hydroxy-2-methyl propionic acid with Acetobacter pasteurianus DSM 8937 is reported. The biotransformation was optimised furnishing (R)-3-hydroxy-2-methyl propionic acid with 97% enantiomeric excess and 100% molar conversion of 5 g/L within 2 h. A simple fed-batch procedure allowed for the obtainment of 25 g/L of the enantiomerically enriched acid. (R)-3-Hydroxy-2-methyl propionic acid is an important building block for the synthesis of Captopril, a widely used antihypertensive drug
Asymmetric reductions of ethyl 2-(benzamidomethyl)-3-oxobutanoate by yeasts
No full textThe stereoselective reduction of ethyl 2–(benzamidomethyl)-3-oxobutanoate 1 using yeasts was investigated among a restricted number (12) of yeasts. Kluyveromyces marxianus var. lactis CL69 diastereoselectively produced (2R,3S)-ethyl 2–(benzamidomethyl)-3- hydroxybutanoate 2, whereas Pichia glucozyma CBS 5766 gave (2S,3S)-2 as the major stereoisomer. The biotransformations were independently optimised for minimizing by-products formation and maximizing the diastereoselectivity. . Under optimised conditions, K. marxianus var lactis CL 69 gave the (2R,3S)-ethyl 2–(benzamidomethyl)-3-hydroxybutanoate 2 with e.e. > 99% and d.e. = 98%, while P. glucozyma CBS 5766 allowed for the obtainment of (2S,3S)-2 with e.e. > 99% and d.e. = 86%
A new chemoenzymatic synthesis of d-cloprostenol
No full textA new chemoenzymatic synthesis Of D-cloprostenol based on the biocatalytical resolution of anti-2-oxotricyclo[2.2.1.0]heptan-7-carboxylic acid 1 has been developed. The resolution was attempted by different approaches: esterification or reduction of the acid and hydrolysis or reduction of the corresponding esters. The most efficient method proved to be the reduction of the propyl esters of 1 catalysed by the yeast Kluyveromyces marxianus, which allowed for the recovery of the enantiomerically pure ester of anti-2-oxotricyclo[2.2.1.0]heptan-(R)-7-carboxylic acid (R)-3 at 60% molar conversion of 3.0 g/l of racemic substrate acid under optimised conditions. anti-2-Oxotricyclo[2.2. 1.0]heptan-(R)-7-carboxylic acid was obtained by alkaline hydrolysis and employed for the synthesis of D-cloprostenol. (c) 2005 Published by Elsevier Ltd
A NEW MACROCYCLIC DIACID WITH BALANCED CONFORMATIONAL FLEXIBILITY AND PREORGANIZATION
No full textMacrocyclic diacid 1 was designed and synthesized as an effective catalyst for hemiacetal cleavage. Molecular modelling studies (using Clark Still's MacroModel) show that 1 has many accessible low energy conformations with various degrees of carboxyl group convergence. A straightforward synthesis of 1 was developed (overall yield ca. 19-20%) starting from commercially available 2,6-dihydroxybenzoic acid. In the key-step, a Cs2CO3-mediated reaction under high dilution and slow addition gave the 28-membered ring of 1 as the only non-polymeric product in 45% yield. The dissociation constants of diacid 1 in a 1:1 H2O/MeOH mixture were measured
Direct conversion of polyconjugated compounds into their corresponding carboxylic acids by Acetobacter aceti
Full text linkThe conversion of polyconjugated aldehydes or alcohols into their corresponding acids was carried out using Acetobacter aceti. The analytical results were compared with those of the acids chemically obtained using a Horner-Wittig reaction
Organic media selection for the extraction of β-hydroxyisobutyric acid produced by microbial biotransformation
No full textThe aim of this work is to evaluate both the toxic effect of different organic media on the stereospecific oxidation of 2-methyl-1,3-propanediol to R-(-)-β-hydroxyisobutyric (HIBA) in two-phase systems and the extraction ability and selectivity of these non-water miscible phases. Apart from traditional solvents, specific organic acid-complexing carriers like TOPO, TOA and Aliquat 336 dissolved in different diluents have been studied. Special interest has been focused on the effect of the concentration of the organic phase extractants and the pH of the aqueous phase on the extraction system. TOPO dissolved in isooctane enabled higher K(p) values at lower concentrations to be attained and resulted in lower toxicity, but its extractive capacity is strongly dependent on the pH. Our results suggest that using a compromise pH value between optimum for bioconversion and extraction, TOPO dissolved in isooctane can be successfully used as an extractive phase for HIBA production in a two-phase system. (C) 2000 Society of Chemical Industry.
The aim of this work is to evaluate both the toxic effect of different organic media on the stereospecific oxidation of 2-methyl-1,3-propanediol to R-(-)-β-hydroxyisobutyric (HIBA) in two-phase systems and the extraction ability and selectivity of these non-water miscible phases. Apart from traditional solvents, specific organic acid-complexing carriers like TOPO, TOA and Aliquat 336 dissolved in different diluents have been studied. Special interest has been focused on the effect of the concentration of the organic phase extractants and the pH of the aqueous phase on the extraction system. TOPO dissolved in isooctane enabled higher Kp values at lower concentrations to be attained and resulted in lower toxicity, but its extractive capacity is strongly dependent on the pH. Our results suggest that using a compromise pH value between optimum for bioconversion and extraction, TOPO dissolved in isooctane can be successfully used as an extractive phase for HIBA production in a two-phase system
Steroid hydroxylations with Botryodiplodia malorum and Colletotrichum lini
No full textAn improved procedure for the microbial hydroxylations of dehydroepiandrosterone (DHEA, 1) and 15β,16β-methylene-dehydroepiandrosterone (2) was studied using whole cells of Botryodiplodia malorum and Colletotrichum lini. C. lini catalyzed 7α- and 15α-hydroxylation of 1 and 7α-hydroxylation of 2, while B. malorum gave 7β-hydroxylation of both the substrates. The stability of the enzymatic activity was higher in the presence of co-substrates (i.e., glucose or mannitol) allowing for repeated batches of the biotransformations. The yields of 7α,15α-dihydroxy-1 production were improved obtaining 5.8 g l−1 (recovered product) from 7.0 g l−1 of substrate. The structures of the hydroxylated products were assigned by a combination of two-dimensional NMR proton–proton and proton–carbon correlation techniques
Chemo- and biocatalytic strategies to obtain phenylisoserine, lateral chain of taxol by asymmetric reduction
No full textEnriched ethyl 3-benzamido-2-hydroxy-3-phenylpropanoate (protected phenylisoserine), the chiral side chain of Taxol, was obtained via asymmetric reduction with transition metal-diphoshine complexes or with whole cells of non-conventional yeasts. Asymmetric hydrogenation was carried out using different approaches: hydrogenation of the tetra-substituted double bond of (E)-1-benzamido-3-ethoxy-3-oxo-1-phenylprop-1-en-2-yl ethyl oxalate 1 with Ir(I)-diphosphine complexes in the presence of TEA, hydrogenation of the carbonyl group of racemic ethyl 3-benzamido-2-oxo-3-phenylpropanoate 2 with Ru(II)-diphoshine complexes in the presence of a Lewis acid and finally a two-step enzymatic transformation of (E)-1-benzamido-3-ethoxy-3-oxo-1- phenylprop-1-en-2-yl ethyl oxalate 1 catalyzed by whole cells of yeasts bearing cell-bound esterases and dehydrogenases
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