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1.
《Tetrahedron: Asymmetry》2014,25(4):298-304
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. 相似文献
2.
《Tetrahedron: Asymmetry》2003,14(11):1495-1501
Enantiotopic selective reduction of 1-(benzofuran-2-yl)ethanones 1a–d, 1-(benzofuran-2-yl)-2-hydroxyethanones 4a–c and 2-acetoxy-1-(benzofuran-2-yl)ethanones 3a–c was performed by baker's yeast for preparation of optically active (benzofuran-2-yl)carbinols [(S)-5a–d, (S)-6a–c and (R)-6a–c, enantiomeric excess from 55 to 93% ee]. 相似文献
3.
《Tetrahedron: Asymmetry》2007,18(4):464-475
In CDCl3 solution, enantiopure (S)-1-benzyl-6-methylpiperazine-2,5-dione (S)-1a formed diastereomeric CO⋯H–N hydrogen-bonded associates with racemic (RS,Z)-1-benzyl-3-[(dimethylamino)methylidene]piperazine-2,5-diones 2a and 2b, (RS)-tert-butyl pyroglutamate (RS)-2c and (RS)-N-benzoylalanine methyl ester (RS)-2d. This resulted in splitting (doubling) of the characteristic signals in the 1H NMR and 13C spectra of racemic compounds 2a–d in the presence of 1 equiv of (S)-1a. The formation of hydrogen-bonded dimers in CDCl3 solution was studied by 1H NMR, 13C NMR and 2D NMR and confirmed by the intermolecular NOE observed between the hydrogen-bonded amide protons from each of the monomeric units, (S)-1a and 2a–c. On the other hand, a slightly different binding mode was proposed for association of (S)-1a with alaninamide (RS)-2d. Enantiomer compositions of known (weighed) mixtures of both enantiomers of tert-butyl pyroglutamate 2c were re-determined by 1H NMR in the presence of (S)-1a in CDCl3. The experimental values were in good agreement with the theoretical values, thus indicating the potential applicability of (S)-1a and related diketopiperazines as chiral solvating agents in NMR spectroscopy. 相似文献
4.
Kinetic resolution of 1-(benzofuran-2-yl)ethanols by lipase-catalyzed enantiomer selective reactions
《Tetrahedron: Asymmetry》2003,14(13):1943-1949
Kinetic resolution of racemic 1-(benzofuran-2-yl)ethanols rac-1a–d was performed by lipase-catalyzed enantiomer selective acylation (E≫100) yielding (1R)-1-acetoxy-1-(benzofuran-2-yl)ethanes (R)-2a–d and (1S)-1-(benzofuran-2-yl)ethanols (S)-1a–d in highly enantiopure form. The degree of enantiomer selectivity for enzymatic alcoholysis/hydrolysis processes starting from racemic 1-acetoxy-1-(benzofuran-2-yl)ethane rac-2 was also tested under various conditions including supercritical CO2 medium. Racemization-free lipase-catalyzed ethanolysis of the (1R)-1-acetoxy-1-(benzofuran-2-yl)ethanes (R)-2a–d yielded almost quantitatively the enantiopure (1R)-1-(benzofuran-2-yl)ethanols (R)-1a–d. 相似文献
5.
The lipase-catalyzed enantioselective acetylation of racemic methyl (4S1,5S1)-4-aryl-5-hydroxyhex-2(E)-enoates 1a–h was performed and efficient resolutions were achieved (E >400) by using CAL-B. After brosylation of the obtained optically active 1a–h, solvolysis of brosylates 13a–h afforded the corresponding methyl (4S1,5S1)-5-aryl-4-hydroxyhex-2(E)-enoates 3a–h (26–94% yield). The yields of 3a and 3c on the solvolysis of the corresponding 13 were 92% and 40%, respectively, while solvolysis of the corresponding tosylate was reported at 70% and 17%, respectively. This procedure is a facile and practical route to the synthesis of bioactive and optically active bisabolane-type sesquiterpenes. 相似文献
6.
Eslam Reda El-Sawy Adel Hamed Mandour Salwa M. El-Hallouty Kamel Hussein Shaker Heba Mohamed Abo-Salem 《Arabian Journal of Chemistry》2013,6(1):67-78
A series of 1-(N-methyl 2a–c and N-benzenesulphonyl-1H-indol-3-yl)-3-aryl-prop-2-ene-1-ones 3a–c were prepared and allowed to react with urea, thiourea or guanidine and gave the pyrimidine derivatives 4a–c to 9a–c. Base catalyzed reaction of 2a–c or 3a–c with ethyl acetoacetate gave cyclohexanone derivatives 10a–c and 11a–c, respectively. Reaction of the latter compounds with hydrazine hydrate afforded indazole derivatives 12a–c and 13a–c, respectively. On the other hand, condensation of 2c or 3c with some hydrazine derivatives namely, hydrazine hydrate, acetyl hydrazine, phenyl hydrazine and benzyl hydrazine hydrochloride gave pyrazole derivatives 14a,b-17a,b, respectively. Moreover, reaction of 2c or 3c with hydroxyl amine hydrochloride gave isoxazole derivatives 18a,b. The newly synthesized compounds were tested for their antimicrobial activity and showed that, compounds 14a, 14b, 15a and 15b were found to be the most active ones of all the tested compounds toward Salmonella typhimurium (ATCC 14,028) compared to the reference drug chloramphenicol. Eighteen new compounds namely, pyrimidin-2(1H)-ones 4a–c and 5a–c, pyrimidin-2(1H)-thiones 6a–c and 7a–c and pyrimidin-2-amines 8a–c and 9a–c were tested for their in vitro cytotoxicity against human liver carcinoma (HEPG2), human breast cancer (MCF7) and human colon cancer (HCT-116) cell lines and showed that, compounds 4c, 5c, 6c, 8c and 9c were found to be the highly active compounds compared to the reference drug doxorubicin. 相似文献
7.
《Tetrahedron: Asymmetry》2006,17(17):2516-2530
(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. 相似文献
8.
《Tetrahedron: Asymmetry》1998,9(2):341-350
Both enantiomers of cis-(±)-2,3-epoxyheptane 1a, cis-3,4-epoxyheptane 1b, cis-3,4-epoxynonane 1c, cis-3,4-epoxynonane-1-ol 1d, and cis-1-methoxy-3,4-epoxynonane 1e undergo a highly stereoselective microsomal epoxide hydrolase catalysed hydration at the (S) carbon to give the corresponding threo (R,R)-diol at complete conversion. A total kinetic resolution of racemic epoxides is also obtained with 1a and 1e. 相似文献
9.
《Tetrahedron: Asymmetry》2004,15(18):2875-2880
Enantiopure β-amino acids 1a–4a and β-lactams 1b–4b were prepared simultaneously through the lipolase-catalysed enantioselective ring opening of unsaturated racemic β-lactams (±)-1-(±)-4. High enantioselectivities (E>200) were observed when the reactions were performed with 1 equiv of water in iPr2O at 70 °C. The resolved (1R,2S)-amino acids (yield⩾45%) and (1S,5R)-, (1S,6R)- and (1S,8R)-lactams (yield⩾47%) could be easily separated. The ring opening of lactam enantiomers 1b–4b with 18% HCl afforded the corresponding β-amino acid hydrochlorides 1c·HCl–4c·HCl (ee >95%). 相似文献
10.
Mohammad Shahabuddin Md. Sharif Hossain Takao Kimura Michinori Karikomi 《Tetrahedron letters》2017,58(48):4491-4495
Diastereomeric resolution of helically distorted polycondensed bisphenols (1,1′-bibenzo[c]phenanthrene-2,2′-diols: HEBPOLs) 2a–b was conducted utilizing (1R)-(?)-menthyl chloroformate as a chiral resolving agent. Subsequent manipulation produced highly optically pure [>99% enantiomeric excess (ee)] quinone derivatives (P) and (M)-1a–b in very good yields. The absolute configuration of each product was confirmed based on circular dichroism (CD) spectra and X-ray crystal structure analysis. 相似文献
11.
Paolo Bonomi Paola Cairoli Daniela Ubiali Carlo F. Morelli Marco Filice Ines Nieto Massimo Pregnolato Paolo Manitto Marco Terreni Giovanna Speranza 《Tetrahedron: Asymmetry》2009,20(4):467-472
(R)-2-Tetralol (R)-2a, (R)-5-hydroxy-2-tetralol (R)-2b and (R)-8-hydroxy-2-tetralol (R)-2c, which are key intermediates in the synthesis of pharmacologically active 2-aminotetralins 3, were prepared in moderate to very high enantiomeric excess (up to 99% ee) by enzymatic resolution of the corresponding racemic butyrates rac-1a, rac-1b and rac-1c, respectively, using lipases immobilized on octyl agarose. This methodology is an alternative to the microbial reduction of 2-tetralones. 相似文献
12.
《Tetrahedron: Asymmetry》1998,9(24):4341-4360
The first enantioselective peroxidation of prochiral allylic and benzylic C–H compounds by the use of chiral bisoxazoline–copper(I) complexes, generated in situ from the ligands 3 and 4a–d, and t-BuOOH as oxidant is reported. Cyclohexene 1, cyclopentene 5, α-angelica lactone 7, allylbenzene 9 and 2-phenylbutane 11 were converted into the optically active allylic and benzylic tert-butyl peroxides 2, 6, 8, 10a and 12 in good yields and ee values of 4–20%. Oxidations of 1-substituted 1-cyclohexenes 13a–c led to mixtures of regioisomeric peroxides 16a–c, 17a–c and 18a–c with different regio- and enantioselectivities, depending on the 1-substituent and the ligand used. The highest ee values (up to 84%) were observed for (S)-3-tert-butylperoxy-1-methyl-1-cyclohexene 17a. 相似文献
13.
《中国化学快报》2007,18(6):636-638
2H-3,1-Pyrazolo[3,4-e]oxazines (5a–c) and tacrine analogies (6a–c) were designed and prepared using 5-amino-4-cyanopyrazole (7) and cycloketones (2a–c) as reactants. The study demonstrated that the new conversion existed in the Friedländer reaction of o-aminocyanopyrazole with cycloketones. 相似文献
14.
《Tetrahedron: Asymmetry》2003,14(13):1917-1923
The chiral monoaza-15-crown-5 type lariat ethers 1 and 2 derived from α-d-glucose and from d-mannitol, respectively, have been applied as phase transfer catalysts in the enantioselective Michael addition of 2-nitropropane to aromatic 3b–c and heteroaromatic 3d–h chalcone analogues. Among the catalysts, the glucose-based 1c with a phosphinoxidobutyl side arm proved to be the most effective, it inducing 34% e.e. for 4b, 59% e.e. for 4c, 80% e.e. for 4d, 64% e.e. for 4e, 17% e.e. for 4f. Catalyst 1a having 3-hydroxypropyl substituent resulted in 81% e.e. for compound 4g. The formation of the (+)-(S)-enantiomer of 4 was preferred using crown ethers 1a–c, while the (−)-(R)-enantiomer was in excess with catalyst 2. The absolute configuration of the Michael adduct 4d was determined by single-crystal X-ray analysis. 相似文献
15.
《Tetrahedron: Asymmetry》1999,10(23):4619-4626
Racemates of cis- and trans-2-(Nβ-t-butoxycarbonyl-Nα-methylhydrazino)cyclopentanols and -cyclohexanols 1–4 were resolved through lipase PS- or Novozym 435-catalysed asymmetric acylation of the secondary OH group at the (R)-stereogenic centre. High enantioselectivity (E >200) was observed when vinyl acetate or vinyl butyrate was used in diisopropyl ether, resulting in the enantiopure hydrazino esters 1a–4a and hydrazino alcohols 1b–4b. Methanolysis of the esters 1a–4a afforded the corresponding 2-hydrazinocycloalkanols 1c–4c (ee usually >95%). 相似文献
16.
《Tetrahedron: Asymmetry》2007,18(3):414-423
The preparation and resolution of the titled conformationally stable biphenyl 1 has been performed in high chemical yield starting from creosol 2. Enantiopure biphenyls (aR)-(+)-1 and (aS)-(−)-1 were obtained by the corresponding menthylcarbonate diastereomer and successive reduction. The absolute configuration and specific rotation were correlated by X-ray analysis of the crystal structure of diastereopure menthylcarbonate (aS,1R,1′R,2S,2′S,5R,5′R)-(+)-16. Preliminary biological evaluation of both racemic enantiomers of 1 has been carried out on melanoma cell lines and significant and selective anticancer activity has been observed for the enantiomer (aS)-(−)-1. 相似文献
17.
《Tetrahedron: Asymmetry》2006,17(2):259-267
The development of three new acidic resolving agents which are hydrogen phthalates of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose 1, 1,2:5,6-di-O-cyclohexylidene-α-d-glucofuranose 2 and 1,2-O-cyclohexylidene-5,6-O-diphenylmethylidene-α-d-glucofuranose 3 is shown for the resolution of 1-arylalkylamines 7a–k. The salts between 1, 2 and (RS)-1-arylalkylamines 7a–k selectively crystallize 1·(S) 7a–j and 2·(S) 7a–h salts, allowing us to recover the corresponding bases (S) 7a–j and (S) 7a–h, respectively, in good yield and enantiomeric excess (73–95% ee). Whereas, the salts between 3 and (RS)-1-arylalkylamines 7a–c,g–i,k selectively crystallize 3·(S)-7a–c,g–i salts to recover the corresponding bases (S)-7a–c,g–i in poor enantiomeric excess (4–35% ee). The difference between the resolving ability of 1 and 2 for 1-arylalkylamines 7a–h is very slight, but there is considerable difference compared to ortho-substituted 1-arylalkylamines 7i and 7j. The role of substituents on a family of resolving agents 1, 2 and 3 is also discussed to interpret their resolving ability. 相似文献
18.
Misako NakamuraTakuya Taniguchi Naohisa IshidaKeishi Hayashi Masahiro MuraokaYohji Nakatsuji 《Tetrahedron》2011,67(48):9298-9304
Kinetic resolution of a racemic mixture of C2-symmetric 18-crown-6 diols (rac-1a) and 15-crown-5 diol (rac-1c) was achieved by lipase-catalyzed acetylation. The enantiomeric excess of the chiral crown diols (95% ee and 82% ee) was determined by 1H NMR spectroscopy, using (R)-(+)-1-(1-naphthyl)ethylammonium hydrochloride as a shift reagent. The C2-symmetric chiral 15-crown-5 diol (>95% ee) was also obtained by kinetic resolution of the racemic diacetate (rac-2c) using lipase-catalyzed solvolysis. 相似文献
19.
《Tetrahedron: Asymmetry》2006,17(23):3193-3196
Twelve-membered cyclic cis- and trans-β-lactams 1b and 2b and the corresponding cyclic cis- and trans-β-amino acid enantiomers, 1a, 1c and 2a, 2c were prepared through the CAL-B-catalysed enantioselective ring cleavage of racemic cis-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-1, and trans-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-2. High enantioselectivities (E >200) were observed for the ring opening of both the cis- and trans-β-lactams when the Lipolase-catalysed reactions were performed with 0.5 equiv of H2O in i-Pr2O at 70 °C. The resolved β-lactams 1b and 2b (yield ⩾47%) and β-amino acids 1a and 2a (yield ⩾32%) could be easily separated. 相似文献
20.
《Tetrahedron: Asymmetry》2001,12(8):1201-1206
Starting from the commercially available (S)-1-phenylethylamine and l-alanine benzylester, we synthesised the homochiral N-alkenoyl aryl azides 2a–2d. The intramolecular cycloaddition of unsubstituted 2a and 2b gave enantiopure 3,3a-dihydro-1,2,3-triazolo[1,5-a][1,4]benzodiazepine-4(6H)-ones 3a, 3b, 4a and 4b, while phenyl-substituted 2c and 2d gave enantiopure 1,1a-dihydro-2H-azirino[2,1-c][1,4]benzodiazepine-4(6H)-ones 5c, 5d, 6c and 6d. 相似文献