中国家猪高分辨G—带及模式图

采用氨甲喋呤或胸苷阻断法使细胞分裂同步化,并结合胰酶G-带技术,对中国7个家猪品种高分辨G-带进行了研究,发现家猪品种间带型基本一致,从而参照人类细胞遗传学命名法的国际体制,提出了中国家猪高分辨G-带标准化核型及模式图,对显带核型界标进行了少许修改,对每对染色体进行了区带划分和描述。单倍染色体组所显示的G-带数目,包括X和Y染色体,巳达444条,近于中期染色体带纹数目的两倍。     

Stereoisomeric flavour compounds XXXV: Chiral aroma compounds of sherry I. Optically pure stereoisomers of solerone and solerole

The enantioseparation of the sherry aroma components 5-oxo-4-hydroxyhexanoic acid γ-lactone (solerone) and 4,5-dihydroxyhexanoic acid γ-lactone (solerole) is achieved, using Chiraspher (Merck) as the chiral HPLC phase and the optical purity ascertained directly by HRGC with heptakis(3-O-acetyl-2,6-di-O-pentyl)-β-cyclodextrin (Lipodex D) as the chiral stationary phase. The absolute configurations of 4,5-dihydroxyhexanoic acid γ-lactones are assigned by ¹H-NMR spectral data of diastereomeric α-methoxy-α-trifluoromethylphenylacetic acid (MTPA) esters, according to Mosher's model. Sensory qualities of the isomers are given.     

A vivid model of chiral recognition

Hands can be used to demonstrate the three-point model of chiral recognition. The points of attachment are thumb, forefinger, and middle finger. This vivid model has the advantages of simplicity, perspicuity, and availability at any time, although two persons are necessary. It can be shown that two interactions are not sufficient for chiral recognition but that three attractive or two attractive and one repulsive attraction are needed. It can also be used to explain some possibilities of weakening or elusion of the three-point model.     

Chiral stationary phase high-performance liquid chromatographic resolution and absolute configuration of enantiomeric benzo[a]pyrene diol-epoxides and tetrols

Enantiomers of diastereomeric benzo[a]pyrene (BP) diol-epoxides, r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydro-BP (BP 7,8-diol-anti-9,10-epoxide), r-7,t-8-dihydroxy-c-9,10-epoxy-7,8,9,10-tetrahydro-BP (BP 7,8-diol-syn-9,10-epoxide), r-9,t-10-dihydroxy-t-7,8-epoxy-7,8,9,10-tetrahydro-BP (BP 9,10-diol-anti-7,8-epoxide), and several 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrenes (BP tetrols) were resolved by high-performance liquid chromatography (HPLC) using columns packed with either (R)-N-(3,5-dinitrobenzoyl)phenylglycine[(R)-DNBPG] or (S)-N-(3,5-dinitrobenzoyl)leucine [(S)-DNBL], which is either ionically or covalently bonded to gamma-aminopropylsilanized silica. Resolution of enantiomers was confirmed by ultraviolet-visible absorption and circular dichroism spectral analyses. Resolved enantiomers of BP diol-epoxides were each hydrolyzed in acidic solution to a pair of diastereomeric tetrols which were separated by reversed-phase HPLC. Absolute stereochemistries of enantiomeric diol-epoxides were deduced by the absolute configuration of their hydrolysis products.     

Identification and quantification of endogenous gibberellins in apical buds and the cambial region of Eucalyptus

Endogenous gibberellins (GAs) were extracted and purified from apical buds of Eucalyptus nitens (Deane and Maid.) Maid. and the cambial region of E. globulus (Labill.). then analysed by capillary gas chromatography-mass spectrometry. GA₁ GA₁₉ GA₂₀ and GA₂₉ were identified by full scan mass spectra. Kovats retention indices and high resolution selected ion monitoring. Using deuterated internal standards. GA₁. GA₁₉. GA₂₀ and putative GA₂₉ and GA₅₃ were quantified in the apical buds, while GA₄. GA₈. GA₉ and GA₄₄ were shown to be either absent or present at very low levels. From the cambial region. GA₁ and GA₂₀ were quantified at levels of 0.30 ng (g fresh weight)-¹ and 8.8 ng (g fresh weight)-¹ respectively. These data suggest that the early 13-hydroxylation pathway is the dominant pathway for GA biosynthesis in Eucalyptus .     

1.56 Å structure of mature truncated human fibroblast collagenase

The X-ray crystal structure of a 19 kDa active fragment of human fibroblast collagenase has been determined by the multiple isomorphous replacement method and refined at 1.56 Å resolution to an R-factor of 17.4%. The current structure includes a bound hydroxamate inhibitor, 88 waters and three metal atoms (two zincs and a calcium). The overall topology of the enzyme, comprised of a five stranded β-sheet and three α-helices, is similar to the thermolysin-like metalloproteinases. There are some important differences between the collagenase and thermolysin families of enzymes. The active site zinc ligands are all histidines (His-218, His-222, and His-228). The presence of a second zinc ion in a structural role is a unique feature of the matrix metalloproteinases. The binding properties of the active site cleft are more dependent on the main chain conformation of the enzyme (and substrate) compared with thermolysin. A mechanism of action for peptide cleavage similar to that of thermolysin is proposed for fibroblast collagenase. © 1994 Wiley-Liss, Inc.     

HPLC and NMR methods for the quantitation of the (R)-enantiomer in (−)-(S)-timolol maleate drug raw materials

HPLC and ¹H-NMR methods for the quantitation of the (R)-enantiomer in (?)-(S)-timolol maleate were developed and validated. The HPLC method requires a 25 cm × 4.6 mm 5 μm Chiracel OD-H (cellulose tris-3,5-dimethylphenylcarbamate) column, a mobile phase of 0.2% (v/v) diethylamine and 4% (v/v) isopropanol in hexane at a flow rate of 1 ml/min and UV detection at 297 nm. A system suitability test was devised to verify the separation of the (R)- and (S)-enantiomers of timolol from other drug-related impurities. The NMR method requires the use of a high-field NMR spectrometer (>360 MHz) and a chiral solvating agent, (?)-(R)-2,2,2-trifluoro-1-(9-anthrylethanol) (R-TFAE). The limits of quantitation were 0.05% and 0.2% (m/m) for HPLC and NMR, respectively. The methods were applied to the determination of the (R)-enantiomer in eight lots of raw material. The results for the two methods were in very good agreement, with results ranging from 0.1 to 4.1% (m/m) by HPLC and none detected to 4.3% (m/m) by NMR. The USP method for specific rotation was found to be unsuitable for detecting the presence of low levels of the (R)-enantiomer in (?)-(S)-timolol maleate. © 1994 Wiley-Liss, Inc.     

Enantiomerization of 2,2′-diisopropylbiphenyl during chiral inclusion gas chromatography: Determination of the rotational energy barrier by computer simulation of dynamic chromatographic elution profiles

By computer simulation of experimental dynamic gas chromatographic elution profiles, the rotational energy barrier ΔG⁼ of racemic 2,2′-diisopropylbiphenyl has been determined as 114.6–115.0 kJ/mol (75–100°C). These data are in good agreement with a value that was determined previously by measuring the racemization kinetics of an enriched sample. This indicates that there is no measurable catalytic or inhibitory effect of the stationary phase. © 1994 Wiley-Liss, Inc.     

Direct resolution of ergot alkaloid enantiomers on a novel chiral silica-based stationary phase

A new covalently-bonded, silica-based stationary phase, using as the chiral selector the 1-(3-aminopropyl) derivative of (+)-(5R,8S,10R)-terguride, has been developed to resolve optically active isomers by HPLC. Good resolution of structurally related racemic ergot alkaloids were obtained using water-methanol mixtures as the eluent. Analysis of the influence of the type and concentration of the organic modifier, and the pH of the buffer in the mobile phase allowed the enantioseparation of these compounds to be optimized. Determination of the optical purity of a lisuride-containig drug is reported. © 1994 Wiley-Liss, Inc.     

Enantioselective separations using capillary electrophoresis

The preconditions are outlined for enantioselective separations in capillary electrophoresis (CE) with chiral selectors as additives to the background electrolyte. Free solution capillary electrophoresis conditions are characterised by a single solution phase. Chiral separations are reviewed by selector type (chiral ligand exchange, cyclodextrins, crown ethers, glycoproteins) with the extensive studies on cyclodextrins grouped into sections on amino acids, pharmaceuticals, and speciality chemicals, optimisation, biological fluids, and quantitative aspects. In micellar electrokinetic capillary chromatography, enantioselective discrimination occurs by partition in a two-phase system, with a chiral micellar phase as selector. Optimum separation conditions can be readily predicted for a given selector–selectand combination, and absolute values of binding constants determined by CE. Advantages of CE in comparison with HPLC using a chiral stationary phase include robust, rapid assays and the use of small volumes of aqueous solutions; disadvantages include less favourable detection limits. © 1994 Wiley-Liss, Inc.