Syntheses of Enantiopure Aliphatic Secondary Alcohols and Acetates by Bioresolution with Lipase B from <em>Candida antarctica</em>

The lipase B from Candida antarctica (Novozym 435^?, CALB) efficiently catalyzed the kinetic resolution of some aliphatic secondary alcohols: (±)-4-methylpentan-2-ol (1), (±)-5-methylhexan-2-ol (3), (±)-octan-2-ol (4), (±)-heptan-3-ol (5) and (±)-oct-1-en-3-ol (6). The lipase showed excellent enantioselectivities in the transesterifications of racemic aliphatic secondary alcohols producing the enantiopure alcohols (>99% ee) and acetates (>99% ee) with good yields. Kinetic resolution of rac-alcohols was successfully achieved with CALB lipase using simple conditions, vinyl acetate as acylating agent, and hexane as non-polar solvent.     

Ultrasound promoted enantioselective transesterification of 3-hydroxy-3-(2-thienyl) propanenitrile catalyzed by lipase

(S)-3-hydroxy-3-(2-thienyl) propanenitrile, which is the key chiral building block for the synthesis of (S)-duloxetine, was successfully prepared via enantioselective transesterification catalyzed by lipase under ultrasound irradiation. Compared with conventional shaking, the enzyme activity and enantioselectivity were dramatically enhanced under ultrasound irradiation. Under optimum reaction conditions (solvent: n-hexane, ultrasound power: 150?W, a_w: 0.33, temperature: 40°C), Pseudomonas sp. lipase exhibited an excellent catalytic performance (enzyme activity: 81.5?μmol?g^?1?min^?1, E-value: 65.4). The reaction achieved its equilibrium in approximately 7?h with a conversion of 53.9% and high enantiopurity (99% ee) of (S)-3-hydroxy-3-(2-thienyl) propanenitrile could be obtained.     

Lipase-catalysed resolution by an esterification reaction in organic solvent of axially chiral (±)-3,3′-bis(hydroxymethyl)-2,2′-bipyridine N,N-dioxide

The enzymatic kinetic resolution of atropisomeric (±)-3,3′-bis(hydroxymethyl)-2,2′-bipyridine N,N-dioxide (±)-3 was investigated via enantioselective esterification in the unusual medium of alcohol/vinyl acetate (20:80). Lipase from Mucor miehei (immobilised lipase preparation, Lipozyme^®) was found to give good enantioselectivity with an (aS)-enantiopreference in the axial recognition, and allowed to efficiently perform the preparation of both enantioforms with ee >98%. Lipase from Pseudomonas cepacia (immobilised lipase preparation, PS-D) also catalysed the reaction although with low enantioselectivity and showing opposite stereopreference.     

Cytotoxic Podophyllotoxin Type-Lignans from the Steam Bark of <em>Bursera fagaroides </em>var. <em>fagaroides</em>

The hydroalcoholic extract of the steam bark of B. fagaroides var. fagaroides displayed potent cytotoxic activity against four cancer cell lines, namely KB (ED₅₀ = 9.6 × 10^-2 μg/mL), PC-3 (ED₅₀ = 2.5 × 10^-1 μg/mL), MCF-7 (ED₅₀ = 6.6 μg/mL), and HF-6 (ED₅₀ = 7.1 × 10^-3 μg/mL). This extract also showed anti-tumour activity when assayed on mice inoculated with L5178Y lymphoma cells. Bioactivity-directed isolation of this extract, afforded seven podophyllotoxin-type lignans identified as podophyllotoxin (1), β-peltatin-A-methylether (2), 5'-desmethoxy-β-peltatin-A-methylether (3), desmethoxy-yatein (4), desoxypodophyllotoxin (5), burseranin (6), and acetyl podophyllotoxin (7) by 1D and 2DNMR and FAB-MS analyses, and comparison with reported values. All the isolated compounds showed potent cytotoxic activity in the cell lines tested, especially compound 3, which exhibited greater activity than camptothecin and podophyllotoxin against PC-3 (ED₅₀ = 1.0 × 10^-5 μg/mL), and KB (ED₅₀ = 1.0 × 10^-5 μg/mL). This is the first report of the isolation of podophyllotoxin and its acetate in a Bursera species.     

A Synthetic Method to Access Symmetric and Non-Symmetric 2-(<em>N</em>,<em>N</em><em>'</em>-disubstituted)guanidinebenzothiazoles

Symmetric and non-symmetric 2-(N-H, N-methyl, N-ethylenyl and N-aryl)guanidinebenzothiazoles were synthesized from the reaction of ammonia, methylamine, pyrrolidine and aniline with dimethyl benzo[d]thiazol-2-yl-carbono-dithioimidate (5) as intermediate. The products were characterized by ¹H-, ¹³C-NMR spectroscopy and three of them by X-ray diffraction analysis. HN-phenyl protons formed intramolecular hydrogen bonds that assist the stereochemistry of the second substituent, whereas the HN-alkyl protons were involved in intermolecular hydrogen bonding.     

Heterocycles 35. CaL-B mediated synthesis of enantiomerically pure (R)- and (S)-ethyl 3-(2-arylthiazol-4-yl)-3-hydroxypropanoates

Herein we present the lipase catalyzed synthesis of four new enantiomerically pure (R)- and (S)-ethyl 3-(2-arylthiazol-4-yl)-3-hydroxypropanoates and their butanoates by enzymatic enantioselective acylation of the racemic alcohols rac-1a–d and by ethanolysis of the corresponding racemic esters rac-2a–d mediated by lipase B from Candida antarctica (CaL-B) in organic solvents. In terms of stereoselectivity and activity, both procedures, the acylation and alcoholysis, are successful (50% conversion, E ≫ 200). The absolute configuration of the resolution products was determined by a detailed ¹H NMR study of the Mosher’s derivatives of (S)-1a.     

Highly efficient double enantioselection by lipase-catalyzed transesterification of (R,S)-carboxylic acid vinyl esters with (RS)-1-phenylethanol

Transesterification of the title compounds using lipase B from Candida antarctica in toluene afforded the corresponding esters in good to excellent diastereomeric excess. (R)-2-Phenylpropionic acid-(R)-1-phenethyl ester 4 was isolated in 45% yield and 64% de after 2.5 h, whereas (R)-2-phenylbutyric acid-(R)-1-phenethyl ester 5 was obtained in 40% yield and 56% de after 35 h. A single recrystallization from n-hexane gave 4 with 98% de. In all reactions CAL-B showed excellent enantioselectivity (E >100) toward (RS)-1-phenylethanol and moderate enantioselectivity (E∼10) toward both carboxylic acid vinyl esters.     

有机相酶催化拆分制备(S)-2-氯-1-(2-噻吩)-乙醇

首次在有机相中对酶催化条件下的2-氯-1-(2-噻吩)-乙醇的反应进行了研究. 通过对不同来源酶的筛选, 找到了Novozym 435和Alcaligenes sp两种选择性较好的酶, 它们均对该反应具有较高的选择性和较快的反应速度, 在此基础上进一步通过对溶剂、温度、摇床转速以及酶用量的筛选, 确定了能够有效拆分2-氯-1-(2-噻吩)-乙醇的较佳反应条件. 当温度35 ℃, 酶量10 mg/mL, 反应72.5 h, 产物的ee值为98.5%时收率为48.6%.     

Preparation,molecular structures,and characteristic properties of (E)-1-(2-furyl)- and (E)-1-(2-thienyl)-2-(3-guaiazulenyl)ethylenes and (E)-1-(3-furyl)- and (E)-1-(3-thienyl)-2-(3-guaiazulenyl)ethylenes

Wittig reactions of 2-furaldehyde (20) [and thiophene-2-carbaldehyde (21)] with (3-guaiazulenylmethyl)triphenylphosphonium bromide (19) in ethanol containing NaOEt at 25 °C for 24 h under argon give (E)-1-(2-furyl)-2-(3-guaiazulenyl)ethylene (22E) and (E)-1-(2-thienyl)-2-(3-guaiazulenyl)ethylene (23E) in 53 and 36% yields. Similarly, Wittig reactions of 3-furaldehyde (29) [and thiophene-3-carbaldehyde (30)] with 19 under the same reaction conditions as for 20 and 21 afford (E)-1-(3-furyl)-2-(3-guaiazulenyl)ethylene (31E) and (E)-1-(3-thienyl)-2-(3-guaiazulenyl)ethylene (32E) in 32 and 46% yields. Molecular structures and characteristic properties as well as preparation of the title E (i.e., one of the geometrical isomers) forms, with a view to comparative study, are reported. Moreover, reactions of those conjugated π-electron systems with TCNE (=tetracyanoethylene) in benzene [and in DMF (=N,N-dimethylformamide)] at 25 °C for 24 h under argon yield unique products, possessing interesting molecular structures, respectively, whose characteristic properties and crystal structures are documented, also.     

Ultrasound- and microwave-assisted synthesis of (E)-1-aryl-3-[2-(piperidin-1-yl)quinolin-3-yl]prop-2-en-1-ones and (E)-1-aryl-3-[2-(pyrrolidin-1-yl)quinolin-3-yl]prop-2-en-1-ones,and their antimicrobial activity

Series of new (E)-1-aryl-3-[2-(piperidin-1-yl)quinolin-3-yl]prop-2-en-1-ones and (E)-1-aryl-3-[2-(pyrrolidin-1-yl)quinolin-3-yl]prop-2-en-1-ones have been efficiently prepared via the Claisen-Schmidt condensation of 2-(piperidin-1-yl)quinoline-3-carbaldehyde and 2-(pyrrolidin-1-yl)quinoline-3-carbaldehyde, respectively, with aryl methyl ketones under conditions of ultrasound and microwave irradiation. Structures of the products have been confirmed by IR, ¹H NMR, ¹³C NMR, and mass spectroscopy, as well as by elemental analysis. Evaluation of the in vitro antibacterial activity against bacterial (Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli) and fungal (Aspergillus niger and Candida metapsilosis) strains has revealed good antimicrobial activity of some of the tested compounds.     

Ultrasound-promoted Lipase-catalyzed Enantioselective Transesterification of (R,S)-Glycidol

Enantioselective transesterification of glycidol with vinyl butyrate as an acyl donor was investigated in the presence of Bacillus subtilis lipase(BSL2) as catalyst. Comparison studies demonstrate the advantage of ultrasound over the conventional shaking for the enzymatic reaction in non-aqueous media. The effects of reaction conditions(ultrasound power, temperature, water activity and pH) on the activity and enantioselectivity were also investigated. Under the optimum conditions, the synthetic activity of BSL2 was 2.95 μmol·min?1·mg?1 and the enantioselectivity(E value) was 52.2. Compared with conventional shaking, ultrasound made the synthetic activity and the enantioselectivity increase 9.5-fold and 1.4-fold, respectively. Furthermore, the repeated use of BSL2 for five cycles resulted in no obvious loss of enzyme activity, suggesting that the enzyme is stable under low power ultrasound conditions.     

Two New Compounds Isolated from<em> Liriope muscari</em>

Two new compounds, (2S,3R)-methyl 7-hydroxy-2-(4-hydroxy-3-methoxy-phenyl)-3-(hydroxymethyl)-2,3-dihydrobenzofuran-5-carboxylate (1) and (4R,5S)-5-(3-hydroxy-2,6-dimethylphenyl)-4-isopropyldihydrofuran-2-one (2), tentatively named norcurlignan and limlactone, respectively, were isolated from Liriope muscari, together with the known compound (-)-pinoresinol (3). The structures of these compounds were elucidated and characterized on the basis of 1D NMR, 2D NMR, CD and MS data. The in vitro antioxidant activities of compounds 1-3 were assessed by the DPPH and ABTS scavenging methods.     

Benzyne-mediated rearrangement of 3-(2-pyridyl)-1,2,4-triazines into 10-(1H-1,2,3-triazol-1-yl)pyrido[1,2-a]indoles

The reaction between 5-R-6-R¹-3-(2-pyridyl)-1,2,4-triazines and benzyne generated in situ in toluene under reflux results in the formation of 10-(1H-1,2,3-triazol-1-yl)pyrido[1,2-a]indoles 3 in up to 60% yields instead of the expected 3-R-4-R¹-1-(2-pyridyl)isoquinolines 2. The crystal structure of product 3c and the proposed mechanism for the formation of 3 are reported.     

Synthesis of enantiopure (R)-2-(4-methoxy-3-(3-methoxypropoxy)-benzyl)-3-methylbutanoic acid—a key intermediate for the preparation of Aliskiren

The enantioselective hydrogenation of (E)-2-(4-methoxy-3-(3-methoxypropoxy)-benzylidene)-3-methylbutanoic acid (1) to (R)-2-(4-methoxy-3-(3-methoxypropoxy)-benzyl)-3-methylbutanoic acid (2)—a key intermediate in the synthesis of the pharmacologically important renin inhibitor Aliskiren—is described. The stereochemistry of the catalytic transformation has been studied using a number of homogeneous chiral Rh(I) and Ru(II) complexes bearing ferrocene-based phosphine ligands. The highest enantioselectivity for the homogeneous hydrogenation of 1 (up to 95% ee) was achieved with a [Rh(NBD)₂]BF₄ pre-catalyst (substrate/catalyst ratio 100:1, 10 bar H₂, 40 °C, in MeOH). To bring the enantioselectivity to perfection an effective method for the isolation of the enantiopure carboxylic acid is suggested likewise.     

<em>N</em>-Substituted 5-Chloro-6-phenylpyridazin-3(2<em>H</em>)-ones: Synthesis, Insecticidal Activity Against <em>Plutella xylostella </em>(L.) and SAR Study

A series of N-substituted 5-chloro-6-phenylpyridazin-3(2H)-one derivatives were synthesized based on our previous work; all compounds were characterized by spectral data and tested for in vitro insecticidal activity against Plutella xylostella. The results showed that the synthesized pyridazin-3(2H)-one compounds possessed good insecticidal activities, especially the compounds 4b, 4d, and 4h which showed > 90% activity at 100 mg/L. The structure-activity relationships (SAR) for these compounds were also discussed.     

Preparation of phosphinoferrocene carboxamides from isocyanates. Synthesis and structural characterisation of palladium(II) and platinum(II) complexes with 1′-(diphenylphosphino)-1-(N-phenylcarbamoyl)ferrocene

The reaction of in situ generated 1′-(diphenylphosphino)-1-lithioferrocene with isocyanates RNCO affords the respective phosphino-carboxamides Ph₂PfcCONHR (fc = ferrocene-1,1′-diyl, R = cyclohexyl (2), and Ph (3)) in moderate yields. The coordination behaviour of 3 chosen as a representative was studied in palladium(II) and platinum(II) complexes. Depending on the metal precursor and the reaction conditions, the following compounds featuring this ligand as a P-monodentate or an O,P-chelating donor were isolated and characterised by spectroscopic methods (IR, multinuclear NMR and electrospray ionisation MS): trans-[PdCl₂(3-κP)₂] (5), trans-[PtCl₂(3-κP)₂] (6), cis-[PtCl₂(3-κP)₂] (7), [SP-4-4]-[(L^NC)PdCl(3-κP)] (8; L^NC = 2-[(dimethylamino-κN)methyl]phenyl-κC¹), and [SP-4-3]-[(L^NC)PdCl(3-κ²O,P)]SbF₆ (9). Besides, the crystal structures of a phosphine oxide resulting by oxidation of 2, viz Ph₂P(O)fcCONHCy (4), and of complexes 5·2Et₂O and 9 have been determined by single-crystal X-ray diffraction analysis.     

Activity-Guided Isolation of Antioxidant Compounds from <em>Rhizophora apiculata</em>

Rhizophora apiculata (R. apiculata) contains an abundance of biologically active compounds due its special salt-tolerant living surroundings. In this study, the total phenolic content and antioxidant activities of various extract and fractions of stem of R. apiculata were investigated. Results indicated that butanol fraction possesses the highest total phenolic content (181.84 mg/g GAE/g dry extract) with strongest antioxidant abilities. Following in vitro antioxidant activity-guided phytochemical separation procedures, lyoniresinol-3α-O-β-arabinopyranoside (1), lyoniresinol-3α-O-β-rhamnoside (2), and afzelechin-3-O-L-rhamno-pyranoside (3) were separated from the butanol fraction. These compounds showed more noticeable antioxidant activity than a BHT standard in the DPPH, ABTS and hydroxyl radical scavenging assays. HPLC analysis results showed that among different plant parts, the highest content of 1-3 was located in the bark (0.068%, 0.066% and 0.011%, respectively). The results imply that the R. apiculata might be a potential source of natural antioxidants and 1-3 are antioxidant ingredients in R. apiculata.     

Kinetic resolution of 5-(hydroxymethyl)-3-phenyl-2-isoxazoline by using the ‘low-temperature method’ with porous ceramic-immobilized lipase

A significant enhancement of the enantioselectivity (E value = 249) in the lipase-catalyzed resolution of a primary alcohol, racemic 5-(hydroxymethyl)-3-phenyl-2-isoxazoline (±)-1, was obtained by using the ‘low-temperature method’ (−60 °C) with porous ceramic-immobilized lipase (Amano PS-C II) and vinyl acetate in acetone.     

Preparation of various enantiomerically pure (benzotriazol-1-yl)- and (benzotriazol-2-yl)-alkan-2-ols

(S)-(−)-(Benzotriazol-1-yl)- and (S)-(−)-(benzotriazol-2-yl)-alkan-2-ols 7a–9a, 7b–9b and their (R)-(+)-acetates 10a–12a and 10b–12b were prepared in high enantiomeric excess via lipase from Pseudomonas fluorescens (Amano AK) catalyzed enantioselective acetylation of racemic alcohols 4a–6a and 4b–6b with vinyl acetate in tert-butyl methyl ether or toluene at 23 °C. The enantioselectivity of this transformation was dependent on the length of the alkyl chain with E-values ranging from 30 to 57. Several benzotriazole substituted ketones 1a–3a and 1b–3b were synthesized from 1H-benzotriazole and corresponding haloketones. These compounds were stereoselectively reduced with Baker’s yeast in water or in organic solvent containing 5% v/v of water at 30 °C to give the (S)-(−)-alcohol. Better stereoselectivity was observed in the kinetic resolution of racemic alcohols 4a–6a and 4b–6b (ee = 69–92% at 44–52% conversion) compared to reduction of corresponding prochiral ketones 1a–3a and 1b–3b with Baker’s yeast (ee = 40–67% at 39–89% conversion). Enhanced enantioselectivities were observed at lower temperatures.     

Synthesis, Antigenicity Against Human Sera and Structure-Activity Relationships of Carbohydrate Moieties from <em>Toxocara</em> larvae and Their Analogues

Stereocontrolled syntheses of biotin-labeled oligosaccharide portions containing the Galβ1-3GalNAc core of the TES-glycoprotein antigen obtained from larvae of the parasite Toxocara and their analogues have been accomplished. Trisaccharides Fuc2Meα1-2Gal4Meβ1-3GalNAcα1-OR (A), Fucα1-2Gal4Meβ1-3GalNAcα1-OR (B), Fuc2Meα1-2Galβ1-3GalNAcα1-OR (C), Fucα1-2Galβ1-3GalNAcα1-OR (D) and a disaccharide Fuc2Meα1-2Gal4Meβ1-OR (E) (R = biotinylated probe) were synthesized by block synthesis using 5-(methoxycarbonyl)pentyl-2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl-(1?3)-2-azide-4-O-benzyl-2-deoxy-α-D-galactopyranoside as a common glycosyl acceptor. We examined the antigenicity of these five oligosaccharides by enzyme linked immunosorbent assay (ELISA). Our results demonstrate that the O-methyl groups in these oligosaccharides are important for their antigenicity and the biotinylated oligosaccharides A, B, C and E have high serodiagnostic potential to detect infections caused by Toxocara larvae.