Synthesis and Rhizopus oryzae mediated enantioselective hydrolysis of α-acetoxy aryl alkyl ketones

Mn(OAc)₃ oxidation of aromatic ketones afforded the α-acetoxy ketones in good yield. Selective hydrolysis of the acetoxy ketones by the fungus Rhizopus oryzae yields (R)-hydroxy ketones in high enantiomeric excess.     

Enzymatic kinetic resolution of tropic acid

A new strategy has been developed for the CAL-B catalysed kinetic resolution of tropic acid by which both enantiomers of tropic acid can be obtained in good enantiomeric excess. (R)-Tropic acid was synthesised with 90% ee and (S)-tropic acid butyl ester in 99% ee by the hydrolysis of tropic acid butyl ester. The other enantiomers were available through the enzymatically catalysed reaction of tropic acid lactone with butanol to give (S)-tropic acid lactone and (R)-tropic acid ester in >98% ee.     

Chemo-enzymatic synthesis of (R)- and (S)-3,4-dichlorophenylbutanolide intermediate in the synthesis of sertraline

3,4-Dichlorophenacylchloride was reduced with whole cell biocatalysts to give the (R)- or (S)-chlorohydrine in high yields and good to high enantiomeric excess. Yields and enantiomeric purity of the (S)-enantiomer were increased to 95 and >98%, respectively, using growing cells from Geotrichum candidum (CBS 233.76) in the presence of hydrophobic adsorbing resins at 4 g/l. The latter compound was transformed into (R)-3,4-dichlorophenylbutanolide, intermediate in the synthesis of (+)-cis-1S,4S-sertraline.     

Resolution of cis-2-fluorocyclopropanecarboxylic acid by a microbial enantioselective hydrolysis

The important key intermediate of quinolone analogue synthesis, (1S,2S)-2-fluorocyclopropanecarboxylic acid, was prepared enantioselectively by a microbial resolution. One of the strains with the highest enzymatic specificity was selected from soil and when lyophilized cells were treated with corresponding ester, the remaining (1S,2S)-ester was obtained with high enantiomeric purity (98% e.e.).     

Application of the asymmetric hydrogenation of enamines to the preparation of a beta-amino acid pharmacophore

(3R)-3-[N-(tert-Butoxycarbonyl)amino]-4-(2,4,5-trifluorophenyl)butanoic acid 7a has been synthesized by an asymmetric hydrogenation of enamine ester 3 using chiral ferrocenyl ligands I and II in conjunction with [Rh(COD)Cl]₂. The direct reduction of 3 provides amino ester 1b in 93% ee, which was isolated as an (S)-camphorsulfonic acid salt to upgrade the enantiomeric excess to >99%. A more concise approach was developed involving the in situ protection of 1b using di-tert-butyldicarbonate. This approach provided the desired N-Boc amino ester 7b directly from the hydrogenation with 97% ee, which was upgraded to >99% ee upon crystallization.     

A third generation chiral phosphorus-containing dendrimer as ligand in Pd-catalyzed asymmetric allylic alkylation

The synthesis of a third generation phosphorus-containing dendrimer possessing 24 chiral iminophosphine end groups derived from (2S)-2-amino-1-(diphenylphosphinyl)-3-methylbutane is described. In situ complexation of this dendrimer by [Pd(η³-C₃H₅)Cl]₂ affords a catalyst, which is used in asymmetric allylic alkylations of rac-(E)-diphenyl-2-propenyl acetate and pivalate. The percentage of conversion, the yield of isolated 2-(1,3-diphenylallyl)-malonic acid dimethyl ester, and its enantiomeric excess have been measured in each case, and were found to be good to very good (ee from 90% to 95%). Furthermore, the dendritic catalyst can be recovered and reused at least two times, with almost the same efficiency.     

Enzyme-catalyzed preparation of methyl (R)-N-(2,6-dimethylphenyl)alaninate: a key intermediate for (R)-metalaxyl

A biocatalytic approach for the production of (R)-metalaxyl, mefenoxam, has been developed. A practical synthesis of methyl (R)-N-(2,6-dimethylphenyl)alaninate, a key intermediate for (R)-metalaxyl, has been developed by the use of lipase-catalyzed hydrolytic kinetic resolution and chemical racemization of the remaining ester. At high concentrations in aqueous media (300 g/L) lipases were stable and gave moderate to good conversions and excellent enantioselectivities (>98% ee). A simple extraction procedure was used to separate the acid product from the remaining ester and the acid was esterified with methanol to give methyl (R)-N-(2,6-dimethylphenyl)alaninate without any reduction in enantiomeric excess (>98% ee). Subsequent chemical coupling with methoxyacetyl chloride provided enantiomerically pure (R)-metalaxyl (>98% ee) without racemization.     

Enhanced Fumaric Acid Production from Brewery Wastewater and Insight into the Morphology of Rhizopus oryzae 1526

The present work explores brewery wastewater as a novel substrate for fumaric acid production employing the filamentous fungal strain Rhizopus oryzae 1526 through submerged fermentation. The effects of different parameters such as substrate total solid concentrations, fermentation pH, incubation temperature, flask shaking speed, and inoculum size on the fungal morphologies were investigated. Different morphological forms (mycelium clumps, suspended mycelium, and solid/hairy pellets) of R. oryzae 1526 were obtained at different applied fermentation pH, incubation temperature, flask shaking speed, and inoculum size. Among all the obtained morphologies, pellet morphology was found to be the most favorable for enhanced production of fumaric acid for different studied parameters. Scanning electron microscopic investigation was done to reveal the detailed morphologies of the pellets formed under all optimized conditions. With all the optimized growth conditions (pH 6, 25 °C, 200 rpm, 5 % (v/v) inoculum size, 25 g/L total solid concentration, and pellet diameter of 0.465?±?0.04 mm), the highest concentration of fumaric acid achieved was 31.3?±?2.77 g/L. The results demonstrated that brewery wastewater could be used as a good substrate for the fungal strain R. oryzae 1526 in submerged fermentation for the production of fumaric acid.     

A biocatalytic one-pot oxidation/reduction sequence for the deracemisation of a sec-alcohol

Biocatalytic deracemisation via inversion of rac-2-decanol was accomplished by a combined oxidation/reduction sequence using the same ‘single’ catalyst for both steps. Overall, the (R)-alcohol was inverted to the corresponding (S)-alcohol. Lyophilised cells of various Rhodococci spp. were tested for the unselective oxidation of the racemic sec-alcohol using acetone as the hydrogen acceptor in the first step. For the second step, the stereoselective asymmetric reduction of the corresponding ketone, 2-propanol was employed as the hydrogen donor. Employing lyophilised cells of Rhodococcus sp. CBS 717.73 racemic 2-decanol was transformed to (S)-2-decanol with excellent enantiomeric excess (92% ee) and yield (82% isolated yield) in the combined one-pot oxidation/reduction sequence.     

Diastereoselective photodeconjugation of chiral α,β-unsaturated esters

Chiral alcohols available in both enantiomeric forms have been tested for the diastereoselective photochemical deconjugation of 2,4-dimethylpentenoic acid esters. (R)-Pantolactone afforded selectively the (2R)-β,γ-unsaturated ester in good yield and high d.e. (89%), while analogous use of (S)-pantolactone gave the (2S)-stereoisomer with similar selectivity.     

Synthesis and antimicrobial activity of some novel 2-(substituted fluorobenzoylimino)-3-(substituted fluorophenyl)-4-methyl-1,3-thiazolines

The synthesis of several 2-(substituted fluorobenzoylimino)-3-(substituted fluorophenyl)-4-methyl-1,3-thiazolines (2a-t) was carried out by base-catalyzed cyclization of corresponding 1-(fluorobenzoyl)-3-(fluorophenyl)thioureas (1a-t) with 2-bromoacetone in aqueous medium. The structures of the synthesized compounds were confirmed by spectral and elemental analysis. All synthesized compounds were evaluated for in vitro antibacterial activity using Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa). The minimum inhibitory concentration (MIC) was determined for the most active compounds. In vitro antifungal activity was also determined against the five fungal species (Rhizopus oryzae, Fusarium oxysporum, Aspergillus terreus, A. niger and A. fumigatus).     

Total synthesis of (−)-sporochnol A,the fish deterrent,from a chiral malonate

From a single chiron, the homochiral benzylic malonic acid ester (R)-(+)-2 available with high enantiomeric excess by enzymatic hydrolysis (PLE acetonic powder), enantiomerically pure (−)-sporochnol A 1 was prepared. This versatile method allows preparation of sporochnol 1, via aldehydes 7 and 15, in good overall yield.     

A practical synthesis of protected β-homolysine

Protected β-homolysine of high enantiomeric purity (ee>99.5%) is prepared utilizing the stereoselective conjugate addition of lithiated (S)-(α-methylbenzyl)benzylamide to (E)-7-(tosyloxy)hept-2-enoic acid tert-butyl ester, followed by subsequent ammonia substitution, Boc protection and removal of the auxiliary.     

A straightforward synthesis of both enantiomers of allo-norcoronamic acids and allo-coronamic acids,by asymmetric Strecker reaction from alkylcyclopropanone acetals

Methylcyclopropanone hemiacetal (2S)-3a underwent the asymmetric Strecker reaction induced by a chiral amine to provide a useful synthesis of enantiomerically pure (1R,2S)-(+)-allo-norcoronamic acid 1 in good yield and high enantiomeric excess. From racemic alkyl hemiacetal (±)-3, the same methodology also constituted a useful way to prepare both (+)-1 and (−)-1 and (+)-allo-coronamic acid 2 and its antipode (−)-2 with good yield and high enantiomeric excess.     

A crystallization-induced asymmetric transformation to prepare (R)-4-chlorophenylalanine methyl ester

A second order asymmetric transformation of racemic 4-chlorophenylalanine methyl ester was achieved via salt formation with (2S,3S)-(−)-tartaric acid in the presence of salicylaldehyde to afford the desired (R)-enantiomer of 4-chlorophenylalanine methyl ester in good yield and high enantiomeric purity.     

(S)-(−)-α-Methylbenzylamine as an efficient chiral auxiliary in enantiodivergent synthesis of both enantiomers of N-acetylcalycotomine

(S)-(−)-α-Methylbenzylamine 2 was used as a chiral auxiliary in the enantiodivergent synthesis of simple isoquinoline alkaloids. The prochiral imine moiety in compound 4 was reduced with different reagents, giving diastereomeric amines 5a or 5b, which subsequently were transformed to either (S)-(−)-N-acetylcalycotomine 6 or (R)-(+)-N-acetylcalycotomine ent-6 in good enantiomeric excess. ¹⁹F NMR of its Mosher's acid ester was used to establish the purities of final compounds.     

Synthesis, characterization and antimicrobial activity of some new 1-(fluorobenzoyl)-3-(fluorophenyl)thioureas

Synthesis of a variety of new 1-(isomeric fluorobenzoyl)-3-(isomeric fluorophenyl)thioureas (1a-t) was accomplished in two steps. The synthetic route involves the reaction of equimolar quantities of isomeric fluorobenzoyl chlorides with potassium thiocyanate in anhydrous acetone to afford the corresponding isothiocyantes in situ, followed by treatment with equimolar quantities of isomeric fluoroanilines. All of the synthesized compounds (1a-t) were screened for their in vitro antibacterial activity using Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aureginosa). The minimum inhibitory concentration (MIC) was also determined for the most active compounds. In vitro antifungal activity was also determined against the five fungal species (Rhizopus oryzae, Aspergillus tereus, Fusarium oxysporum, Aspergillus niger, Aspergillus fumigatus). In general, the antifungal activity of compounds was better than their antibacterial activity.     

Effect of the alkyl chain length of 1,1′-binaphthyl esters in lipase-catalyzed amidation

Lipase-catalyzed amidation of 2-[2-(ethoxycarbonyl)ethyl]-1,1′-binaphthyl [(±)-3] yielded optically active (S)-3 and 2-[2-(2-cyanoethylaminocarbonyl)ethyl]-1,1′-binaphthyl [(R)-6a] with high enantiomeric excess. For these lipase-catalyzed amidations, the optimal alkyl chain length between the binaphthyl ring and the ester group was determined to be an ethylene spacer.     

Synthesis of polynucleotide analogs by grafting optically active adenine,cytosine, and hypoxanthine derivatives onto polytrimethylenimine

A new family of polynucleotide analogs were prepared by grafting nucleic acid base derivatives onto polytrimethylenimine. Several new optically pure α-nucleic acid base substituted propanoic acids were prepared as pendant groups. The (R)-ethyl adeninylpropanoate was obtained from adenine and (S)-ethyl lactate by utilizing a diethyl azodicarboxylate-triphenyl phosphine method. Subsequent hydrolysis of the ester in aqueous acid gave the (R)-adeninylpropanoic acid without racemization. The reaction of cytosine sodium salt with (S)-ethyl 2-[(methylsulfonyl)oxy] propanoate produced the 20% racemized (R)-ethyl 2-(cytosin-1-yl)propanoate. The optically pure ester was obtained by recrystallization from ethyl alcohol, which was hydrolyzed in aqueous acid to give the (R)-acid with 66% enantiomeric excess. The (R)-2-(hypoxanthin-9-yl)propanoic acid was prepared by reaction of (R)-2-(adenin-9-yl)propanoic acid with sodium nitrite. The pendant groups were allowed to react with N-hydroxy compounds in the presence of dicyclohexylcarbodiimide to give the active esters. These active esters underwent reaction with N,N-dipropylamine to provide monomer model compounds. The pendant groups were grafted onto polytrimethylenimine by using the active ester method. The racemization reactions were observed in the grafting reactions. The resulting polymers showed a range of percent grafting from 60 to 80%.     

Enhanced enantioselectivity in the heterogeneous catalytic hydrogenation of acetoacetate esters into the corresponding 3-hydroxybutyrates using commercial nickel powder

Heterogeneous catalytic hydrogenation of acetoacetic acid esters over tartaric acid/NaBr-modified Ni powder was determined to be a critical function of the steric bulk of the ester moiety to afford quantitatively 3-hydroxybutyrate in 94% enantiomeric excess when ethyl and i-butyl esters are used, providing a facile route to optically active 3-hydroxybutyrates.