O.A.C. Antunes

Lipase-catalyzed diacylglycerol production under sonochemical irradiation☆

The present paper describes a protocol for production of diacylglycerol by the partial hydrolysis of soybean oil catalyzed by lipase under ultrasound irradiation. Better yields and shorter reaction times were obtained under sonication as compared to the thermal process.

Autoxidation of limonene, α-pinene and β-pinene by dioxygen catalyzed by Co(OAc)2/bromide

Abstract It has been shown that NaBr addition to Co(OAc) 2 increases conversions in autoxidations, by dioxygen, of limonene ( 1 ), α-pinene ( 2 ) and β-pinene ( 3 ). Best selectivities towards allylic oxygenated products were achieved with an optimum ratio [Co(OAc) 2 ] [NaBr] = 1 , while keeping [Co(OAc) 2 ] = 0.15 M. Using this system selectivities of 24.1, 11.4, 14.8 and 20.6% were obtained, respectively for carvone ( 4 ), trans -carveol ( 7a ), trans - and cis -carvoyl acetate ( 9a and 9b ) and 4-acetoxy- p -mentha-1,8-diene ( 13 ) from limonene ( 1 ). Autoxidation of α-pinene ( 2 ) showed selectivities of 10.2, 19.5 and 29.5% for myrtanal ( 6 ), verbenone ( 5 ) and trans -verbenyl acetate ( 17a ), respectively. Very good selectivities, 19 and 15.4%, were observed for terpinyl acetate ( 27 ) and myrtanal ( 6 ) from autoxidation of β-pinene ( 3 ). Substitution of Co(II) by Mn(II) up to 30% M had no effect on conversions. However, this substitution (20–30% M) shifted selectivity significantly towards alcohols and acetates , yielding selectivities of 20 and 18% for trans -carveol ( 7a ) and trans - and cis -carvoyl acetate ( 9a and 9b ) from limonene ( 1 ); 48% for verbenyl acetate ( 17a ) from α-pinene ( 2 ) and 16–18% for trans -pinocarveol ( 16 ) from β-pinene ( 3 ). It was concluded that, in this case, Mn(II) exercises a selectivity tuning effect.

Simultaneous enzymatic synthesis of (S)-3-fluoroalanine and (R)-3-fluorolactic acid

Abstract A coupled enzymatic system for the simultaneous synthesis of ( S )-3-fluoroalanine ( 1a ) and ( R )-3-fluorolactic acid ( 3 ) with l -alanine dehydrogenase ( l -AlaDH) from Bacillus subtilis and rabbit muscle l -lactate dehydrogenase ( l -LDH) using rac - 1 and NAD + is described. Analysis of isolated products of the laboratory preparative scale process revealed 1a in 60% yield and 88% ee and 3 in 80% yield and over 99% ee. The compounds 1a and 3 represent chiral building blocks for the synthesis of several products with pharmacological activity.

Catalase vs Peroxidase Activity of a Manganese(II) Compound: Identification of a Mn(III)―(μ-O)2―Mn(IV) Reaction Intermediate by Electrospray Ionization Mass Spectrometry and Electron Paramagnetic Resonance Spectroscopy

Herein, we report reactivity studies of the mononuclear water-soluble complex [Mn(II)(HPClNOL)(eta(1)-NO(3))(eta(2)-NO(3))] 1, where HPClNOL = 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, toward peroxides (H(2)O(2) and tert-butylhydroperoxide). Both the catalase (in aqueous solution) and peroxidase (in CH(3)CN) activities of 1 were evaluated using a range of techniques including electronic absorption spectroscopy, volumetry (kinetic studies), pH monitoring during H(2)O(2) disproportionation, electron paramagnetic resonance (EPR), electrospray ionization mass spectrometry in the positive ion mode [ESI(+)-MS], and gas chromatography (GC). Electrochemical studies showed that 1 can be oxidized to Mn(III) and Mn(IV). The catalase-like activity of 1 was evaluated with and without pH control. The results show that the pH decreases when the reaction is performed in unbuffered media. Furthermore, the activity of 1 is greater in buffered than in unbuffered media, demonstrating that pH influences the activity of 1 toward H(2)O(2). For the reaction of 1 with H(2)O(2), EPR and ESI(+)-MS have led to the identification of the intermediate [Mn(III)Mn(IV)(mu-O)(2)(PClNOL)(2)](+). The peroxidase activity of 1 was also evaluated by monitoring cyclohexane oxidation, using H(2)O(2) or tert-butylhydroperoxide as the terminal oxidants. Low yields (<7%) were obtained for H(2)O(2), probably because it competes with 1 for the catalase-like activity. In contrast, using tert-butylhydroperoxide, up to 29% of cyclohexane conversion was obtained. A mechanistic model for the catalase activity of 1 that incorporates the observed lag phase in O(2) production, the pH variation, and the formation of a Mn(III)-(mu-O)(2)-Mn(IV) intermediate is proposed.

Oxidation of α- and β-pinene catalyzed by MnIII (Salen) Cl·H2O

The cationic complex MnIII (Salen) is a very effective catalyst for the oxidation of bothα- andβ-pinene. The higher selectivity towards epoxide formation supports the rebound oxygen mechanism. A turnover of 40 was obtained for both compounds after 16 h of reaction with a molar ratio 1∶0.01∶1 (feedstock: catalyst: iodosobenzene) and conversions between 50 and 60% were observed. A very high selectivity (55%) was determined for epoxide formation from α-pinene. The good selectivity observed for myrtanal isomers (6.5 and 23.2%) fromβ-pinene is related to the prior formation of the 1,2-epoxides.

Resolution of dl-hydantoins by d-hydantoinase from Vigna angularis: Production of highly enantioenriched N-carbamoyl-d-phenylglycine at 100% conversion

Summary.d-Hydantoinase from Vigna angularis hydrolyzed rac-5-monosubstituted-hydantoins with polar and aromatic side chains and dihydrothymine but rac-5,5-disubstituted-hydantoins were not substrates of this enzyme. 5-Phenylhydantoin was the best substrate. By using this substrate, N-carbamoyl-d-phenylglycine was obtained in quantitative yield and over 98% ee.

Microbiological enantioselective reduction of ethyl acetoacetate

Abstract Different microorganisms (MOs) were used to carry out the enantioselective reduction of ethyl acetoacetate to (S)-(+)-3-hydroxybutanoate or (R)-(−)-3-hydroxybutanoate. Surprisingly, the commercially available Saccaromyces cerevisiae led to only 58% ee of (S)-(+)-3-hydroxybutanoate. Other MOs such as Hansenula sp. and Dekera sp. furnished the same enantiomer with greater ees, 81 and 73%, respectively. Aspergilus niger and Kluyveromyces marxianus although leading to lower ees, 30 and 18%, yielded the opposite enantiomer. All reactions proceeded to greater than 85% conversion. This is the first report on the use of Hansenula sp. and Dekera sp. in reductions of β-ketoesters.

Oxidation of limonene catalyzed by MnIII(Salen)Cl-H2O

The cationic MnIII(Salen) complex was proved to be an effective catalyst for the oxidation of limonene with iodosobenzene as terminal oxidant. For reactions conducted in CH2Cl2 at rt, with molar ratio of 1 ∶ 0.05 ∶ 1 (limonene: catalyst: iodosobenzene) limonene oxidation does occur with an optimal conversion of 60%. The major products according to HRGC-MS and HRGC-IR analyses were cis- and trans-l,2-epoxylimonene (30% and 16.7%, selectivity, respectively), the two diastereoisomers of 1p-menthen-9-al (20% selectivity), and carvone (10% selectivity). A turnover of 60 was observed at 1 ∶ 0.01 ∶ 1 ratio. The higher selectivity toward epoxide formation supports the rebound oxygen mechanism.

Oxidation of limonene catalyzed by Metal(Salen) complexes

The compound R-(+)limonene is available and cheap than its oxidized products. Consequently, the selective oxidation of R(+)limonene has attracted attention as a promising process for the production of compounds with a higher market value, such as cis/trans-1,2-limoneneoxide, cis/trans-carveol and/or carvone. One of the these processes, described in the recent literature, is submission of R-(+)limonene to an oxidation reaction catalyzed by neutral or cationic Metal(Salen) complexes, in the presence of effective terminal oxidants such as NaOCl or PhIO. These reactions are commonly carried out in organic solvents (dichromethane, ethyl acetate, acetonitrile or acetone). Thus, the main objective of the present work was to study the effect of several factors (type of oxidant, catalyst, solvent and time) on reaction selectivity for the high-priced compounds referred to above. For this purposes, experimental statistical multivariate analysis was used in conjunction with a complete experimental design. From the results it was observed that for the three targeted products (1,2-limoneneoxide, carveol or carvone) some factors, including the nature of the terminal oxidant and the catalyst, were significant for product selectivity (with a confidence level of 95%). Therefore, this statistical analysis proved to be suitable for choosing of the best reaction conditions for a specific desired product.

Stability of immobilized D-hydantoinase from Vigna angularis and repeated cycles of highly enantioenriched production of N-carbamoyl-D-phenylglycines

Summary.D-hydantoinase from Vigna angularis was immobilized by covalent linkage to aminopropyl glass beads. Thermal stability, resistance to storage at different pH values and temperatures of this biocatalyst were studied. This enzyme preparation was used as a catalyst to prepare enantioenriched N-carbamoyl-D-phenylglycine, N-carbamyl-D-p-fluorophenylglycine and N-carbamoyl-D-p-trifluoromethylphenylglycine, using a stirred batch reactor. Reactions were conducted during eight repeated reaction cycles, without loss of enzymatic activity or variation of the enantiomeric excess of the respective product (>98%).