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1.
We report here a novel synthesis of optically active bishomotyrosine. The bishomotyrosine skeleton was constructed by using a Friedel-Crafts reaction between phenol and optically active N-Tfa-Glu(Cl)-OMe in triflic acid under the mild condition. Reduction and subsequent deprotection then afforded bishomotyrosine derivatives without any loss of optical purity.  相似文献   

2.
Takada H  Oda M  Oyamada A  Ohe K  Uemura S 《Chirality》2000,12(5-6):299-312
The copper-catalyzed diastereoselective imidation of diaryl sulfides bearing a chiral oxazolinyl moiety at the ortho-position with [N-(p-toluenesulfonyl) imino]phenyliodinane (TsN=IPh) or Chloramine-T trihydrate [TsN(Cl)Na.3H2O] was successfully carried out to give the corresponding optically active N-tosylsulfimides in good yields. For example, the imidation of diphenyl sulfide bearing a methoxymethyl moiety at the 4-position of the oxazoline ring with TsN(Cl)Na.3H2O in acetonitrile in the presence of 10 mol% Cu(OTf)2 at 25 degrees C for 24 h affords the corresponding optically active N-tosylsulfimide in 52% isolated yield with a high diastereoselectivity of 99%. Hydrolysis of the optically active N-p-tosylsulfimides converts them into the corresponding optically active sulfimides in high yields without loss of diastereoselectivity. These novel optically active sulfimides and N-tosylsulfimides work as efficient chiral ligands for palladium(II)-catalyzed allylic alkylation of 1, 3-diphenyl-3-acetoxy-1-propene with dimethyl malonate to give the corresponding alkylation product quantitatively and with a high stereoselectivity (up to 90% ee).  相似文献   

3.
A series of racemic and optically active oxiranes, bearing mesogenic groups, precursors of liquid crystalline polyethers, has been synthesized from epichlorohydrin or glycidol. The enantiomeric excess of the optically active oxiranes has been determined by chiral stationary phase HPLC. Compounds bearing 4-cyanobiphenyl mesogenic group exhibit monotropic liquid crystalline behavior. A transfer of chirality to the mesophase has been observed for the optically active oxiranes, which present a cholesteric phase. Chirality 10:779–785, 1998. © 1998 Wiley-Liss, Inc.  相似文献   

4.
Dissymmetric combinations of weak natural fields exert a stereospecific effect, which may result under some conditions characteristic of outer space in the formation of appreciable amounts of optically active compounds. Synthesis of optically active matter could occur in the early stages of the formation of the Solar System.  相似文献   

5.
The surface of dried drops of blood serum (BS) from 86 plasmapheresis patients with atherosclerosis has been studied for its structural peculiarities. The content of lipids (total cholesterol, cholesterol of lipoproteins of high density, triglycerides), sialic acids and immunoglobulins was determined in all the examinees. BS from 20 practically healthy people was taken as a control. Optically inactive filamentous dichotomically branching crystals were typical of its microstructure. Optically active spherolites were found in patients with high content of cholesterol, optically active dendrite aggregation--in patients with high content of triglycerides, optically active fibrils appeared in case of hypersialemia, optically inactive aggregates--in case of hyperimmunoglobulemia. The plasmapheresis course carried out in patients was followed by appearance of filamentous dichotomically branching crystals, and disappearance of optically active inclusions, that testified to ordering of the BS structure. The results obtained were confirmed by normalization of the content of lipids, sialic acids, immunoglobulins.  相似文献   

6.
U.S. Food and Drug Administration issues certain guidelines for marketing of optically active drugs as some enantiomers racemize into human body, leading to the generation of other antipodes, which may be toxic or ballast to the human beings. Moreover, racemization reduces the administrated dosage concentration as optically active enantiomer converted into its inactive counter part. Therefore, the study of racemization of such type of drugs is an important and urgent need of today. This article describes in vitro and in vivo racemization of optically active drugs. The racemization process of various optically active drugs has been discussed considering the effect of different variables i.e. pH, temperature, concentration of the drug, ionic concentration, etc. Attempts have also been made to discuss the mechanisms of racemization. Besides, efforts have been made to suggest the safe dosages of such type of drugs too.  相似文献   

7.
Achiral 4-isopropyltropolone methyl ether (3) included in an optically active host compound (-)-1 yielded optically active photocyclization products (-)-5 and (-)-6 in 96 and 90% ee, respectively, upon photoirradiation in the solid state.  相似文献   

8.
It is shown that natural chiral catalysts, which could be formed e.g., from optically active amino acids on basic natural minerals, could lead, at early stages of evolution, to the formation of rather complex optically active products from starting achiral compounds. Using biomimetic combinations of vanadium ion complexes and chiral ligands synthesized from widely occurring natural compounds, we created novel catalytic systems, permitting the transfer of optical activity in the course of catalytic chemical transformations of achiral compounds. We found that in the presence of natural clay, optically active terpenoids from the pinane series undergo multistage transformations, forming unexpected new products with preservation of optical purity.  相似文献   

9.
A new insoluble polymer containing a Cinchona alkaloid derivative has been synthesized and used as chiral ligand in the heterogeneous enantioselective dihydroxylation of olefins. It is shown that the enantioselectivity of the optically active diols obtained from both aliphatic and aromatic substrates is always comparable to that observed in the homogeneous phase under the same reaction conditions. A method for evaluating the enantiomeric excesses of the optically active products is also described. © 1995 Wiley-Liss, Inc.  相似文献   

10.
A novel manganese(III) complex having an optically active N, N′-ethylenebis-β-ketoimine ligand was prepared and characterized crystallographically. The manganese(III) complexes behave as effective catalysts in enantioselective epoxidation of unfunctionalized olefins by combined use of molecular oxygen, an oxidant, and pivalaldehyde, a reductant. Dihydronaphthalene derivatives were converted into the corresponding optically active epoxides with good to high enantioselectivities.  相似文献   

11.
The optically active lipid A-subunit homologs named GLA-46, GLA-47, GLA-59, and GLA-60 have been synthesized stepwise by successive acylation at N-2 and O-3 of benzyl 2-amino-2-deoxy-4,6-O-isopropylidene-beta-D-glucopyranoside with the 3-9O-(benzyloxy)methyl or 39O-tetradecanoyl derivative of optically active 3-hydroxytetradecanoic acid, and phosphorylation at O-4 of the D-glucosamine residue.  相似文献   

12.
Radical polymerization of N-p-vinylbenzyl-D-lactonamide (VLA) gave an optically active helical polymer. The stereoregularity of poly(N-p-vinylbenzyl-D-lactonamide) (PVLA) measured by 13C NMR spectroscopy showed a well-resolved sharp-line width, which was assigned to the phenyl C-1 carbon of the isotactic polystyrene (PS). The helical structure of PVLA shown by circular dichroism (CD) indicated that the aromatic groups were chirally supramolecular-packed giving optically active disaccharide units in the side chain covalently linked via an amide linkage with PS, the original PS not being optically active. The intensity of CD for PVLA (a) decreased with increasing temperature due to the change in the conformation of the phenyl group or to the breakdown of intermolecular hydrogen bonding of amide groups and (b) increased in a mixture of water and alcohol due to the increased hydrophobicity. The CD intensity for maltose-carrying PS (PVMA) was slightly higher than that of PVLA CD due to the more hydrophobic property of PVMA than PVLA.  相似文献   

13.
Of 25 commercial lipases, nine were able to catalyse the hydrolysis of ethyl D,L-2-amino-4-phenylbutyrate (D,L-APBAE) to optically active D-APBAE, an intermediate for the synthesis of inhibitors of angiotensin-converting enzyme, with specific selectivity ranging between 3.7 and 12.5. Optimal conditions for porcine pancrease lipase-catalyzed reaction gave a 68% conversion and the D-ester was obtained by a simple extraction with an optical purity of 98%. Saponification of the ethyl ester of D-APBA in 1 M NaOH gave the optically active D-APBA with a chemical purity greater than 99%.  相似文献   

14.
The diffusion rates of nalidixic acid, ofloxacin and ofloxacin's two optically active isomers through OmpF channels were measured in proteoliposomes and compared with the rates of beta-lactams. The four quinolones showed high diffusion rates, exceeding that of cephaloridine and being comparable to imipenem. There was no significant difference in diffusion rate between nalidixic acid and ofloxacin, or between the two optically active isomers. The diffusion rates of enoxacin and norfloxacin were also estimated to be higher than many beta-lactams.  相似文献   

15.
The optically active building blocks for organic synthesis: tertiary carbinols, antitumor lignan, liquid crystals, 1,3-diene and biscyclopropyl compounds were synthesized through lipase-catalyzed reaction. This paper discusses ways in which organic chemists can expand the applicability of lipase-catalyzed reactions for use in designing a synthetic strategy. Several excellent examples are described in which lipase-catalyzed reactions were involved as the key steps. Because lipase-catalyzed reactions often offer insufficient enantioselectivity, a new method to enhance the enantioselectivity of a lipase-catalyzed reaction was demonstrated. Thiacrown ether technology was typically used to synthesize new optically active ,-difluoro-γ-lactone.  相似文献   

16.
Efficient enzyme catalyzed kinetic resolutions of a synthetically useful chiral building block, (Z)-4-triphenylmethoxy-2,3-epoxybutan-1-ol, are reported. The highest selectivities were achieved by Lipozyme TL IM and Amano Lipase PS enzymes in the presence of vinyl acetate. Enantiomeric enrichment of the optically active acetate isomer was accomplished by selective crystallization of the racemic part of the enantiomeric mixture. Enzyme catalyzed hydrolysis of the acetate also provided an optically pure epoxybutanol derivative. O-Benzylation of (+)-(Z)-1-hydroxy-4-triphenylmethoxy-2,3-epoxybutane followed by super base promoted diastereo- and enantio-selective rearrangement resulted in (+)-(2R,3R,1'R)-3-[1-hydroxy-2-(triphenylmethoxy)ethyl]-2-phenyloxetane in >98% ee and de. Configurations of the new optically active products were determined by chemical correlation.  相似文献   

17.
An optically active key intermediate, methyl 2, 4-dideoxy-4-C-carboxymethylene-α-d-ribo-hexopyranoside 2′→3 lactone (XII), for the syntheses of optically active Thromboxanes was prepared from d-glucose.  相似文献   

18.
Allylic hydroperoxides are a class of compounds of versatile synthetic utility. Optically active diastereomeric hydroperoxy homoallylic alcohols and their corresponding diols are easily available through horseradish peroxidase (HRP)-catalyzed kinetic resolution of racemic hydroperoxides. Here we describe the assignment of the absolute configuration of the optically active products and substrates obtained after HRP-catalysis by the circular dichroism exciton chirality method. Moreover, the analytical-scale separation of the enantiomers based on multidimensional gas chromatography on chiral columns is presented. Since the enantiomeric elution order on the ciral columns was constituted, the absolute stereochemistry of optically active allylic diols can easily be deduced by their retention times on β-cyclodextrins. Chirality 9:69–74, 1997. © 1997 Wiley-Liss, Inc.  相似文献   

19.
Two sesquiterpenoid naphthols, 2,7-dihydroxycadalene and 2-hydroxy-7-methoxycadalene, have been isolated from green and field-dried cotton bracts. These naphthols rapidly autoxidize on silica gel to lacinilene C and lacinilene C 7-methyl ether, respectively. The latter compound has been implicated as a causative of byssinosis. Lacinilene C and its methyl ether derivative isolated from field-dried cotton leaves and bracts were optically active, indicating that the lacinilenes are produced enzymatically from the naphthols. Therefore, bioassays for byssinotic activity using racemic synthetic lacinilene C 7-methyl ether, rather than the naturally occurring optically active compound, must be scrutinized carefully.  相似文献   

20.
We studied the spontaneous formation of chiral crystals of four diaryl ethers, 3‐phenoxybenzaldehyde, 1 ; 1,3‐dimethyl‐2‐phenoxybenzene, 2 ; di(4‐aminophenyl) ether, 3 ; and di(p‐tolyl) ether, 4 . Compounds 1 , 3 , and 4 form conformationally chiral molecules in the solid state, while the chirality of 2 arises from the formation of supramolecular helices. Compound 1 is a liquid at ambient temperature, but 2 , 3 , 4 are crystalline, and solid‐state CD‐spectroscopy showed that they could be obtained as optically active bulk samples. It should be noted that the optical activity arise upon crystallization, and no optically active precursors were used. Indeed, even commercial samples of 3 and 4 were found to be optically active, giving evidence for the ease at which total spontaneous resolution may occur in certain systems. Chirality 27:425‐429, 2015. © 2015 Wiley Periodicals, Inc.  相似文献   

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