摘要:

AbstractA method for the separation and identification of complex mixtures of more than 50 different intact esters in epicuticular wax of swede,Brassica napusvar.rapiferacv. Doon Major, using combined gas chromatography‐mass spectrometry (GC‐MS) has been developed. The esters were separated at temperatures of up to 350°C by automatic pressure programming (for capillary GC) or by manually increasing helium carrier gas pressure (for GC‐MS) in order to maintain flow at high temperatures. Esters in the range C41‐C50were detected, with regular repeating acid/alcohol combinations. Individual acid and alcohol moieties were identified from [RCO2H2]+ions in the mass spectra of intact esters and, following trans‐esterification and silylation, from the mass spectral and chromatographic characteristics of the methyl esters of the acid components (C14‐C23) and trimethylsilyl derivatives of the alcohol components (C23‐C31). The major compounds were doubly branched C44and C46esters, composed ofanteiso‐C17/anteiso‐C27(32.7%),anteiso‐C17/anteiso‐C29(11.9%) andanteiso‐C19/anteiso‐C27(13.1%) acid/alcohol combinations, respectively, singly branched C43and C45esters, composed of n‐C16/anteiso‐C27(8.5%),anteiso‐C17/n‐C26(3.9%), n‐C18/anteiso‐C27(6.8%),anteiso‐C17/n‐C28(2.3%) andante

ISSN:0958-0344    

DOI:10.1002/pca.2800060202

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractOat straw was treated with different chemical reagents to remove specific components from the cell walls. The effects of these treatments were investigated using traditional wet‐chemical analyses and pyrolysis mass spectrometry (Py‐MS) in both electron impact and chemical ionization modes. Separate treatments with permanganate and chlorite dissolved the major portion of the lignin, while alkaline peroxide treatment dissolved a proportion of the non‐cellulose polysaccharides (NCPs). Combined chlorite and sodium hydroxide treatments removed most of the lignin and NCPs whereas peracetic acid treatment showed a slight decrease in both NCPs and lignin contents. Py‐MS thus confirmed the wet chemistry results by showing reductions in the ion markers for both lignin and NCPs, where appropriate. In addition, Py‐MS showed other changes, such as the removal of phenolic acids, in a single analysis while differences between the residues from permanganate and chlorite treatment were also observed even though the chemical analyses gave virtually identica

ISSN:0958-0344    

DOI:10.1002/pca.2800060203

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA liquid chromatography procedure which rapidly separates the two isomers of schumannificine and N‐methylschumannificine, chromone alkaloids isoilated fromSchumanniophyton magnificum(Rubiaceae), is described. The procedure uses a porous graphitic carbon high performance liquid chromatographic column and is compared with other chromatographic and chemical methods which were tried unsuccessfully. The method was adapted in an attempt to prepare the individual isomers of schumannificine and N‐methylschumannificine in mg amounts but interconversion of the isomers in aqueous medium was shown to occur too rapidly for this to be feasi

ISSN:0958-0344    

DOI:10.1002/pca.2800060204

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractQuaternary alkaloids of the stem ofZanthoxylum usambarense, an important medicinal plant in Kenya utilized for the treatment of pneumonia and rheumatism, were examined by a combination of ion‐pair extraction and preparative ion‐pair high performance liquid chromatography (HPLC), in which sodium perchlorate was used as an ion‐pair reagent. Quaternary bases were extractable from aqueous solution into 1,2‐dichloroethane in the presence of perchlorate in acidic conditions. The phenomenon is explained in terms of ion‐pair extraction between alkaloidal cation and perchlorate anion. The quaternary alkaloidal fraction thus obtained was well separated by means of ion‐pair HPLC in which sodium perchlorate was also utilized. Furthermore, the solvent system was easily applied to preparative HPLC, yielding the pure perchlorate of each alkaloid. Eight quaternary bases inZ. usambarensewere thus obtained and their structures were elucidated. One of them was a new quaternary base of the tetrahydroprotoberberine type, which was named (

ISSN:0958-0344    

DOI:10.1002/pca.2800060205

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSeventeen different samples ofPassiflora incarnatawere screened for harman alkaloids by a reversed‐phase high performance liquid chromatographic (HPLC) method. Only one sample yielded a possible harman content of approximately 0.1 ppm which was just above the level of detection limit. The method comprises extraction of the plant material, purification and concentration of the alkaloid fraction by combined solid‐phase extractions on Extrelut and cation‐exchange cartridges, and subsequent HPLC analysis using diode‐array and fluorescence detection. The method was found to be sensitive and selective and revealed good recovery. The efficiency of the method was demonstrated withPeganum harma

ISSN:0958-0344    

DOI:10.1002/pca.2800060206

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA rapid sensitive and reliable reverse phase high performance liquid chromatography method was developed using a Taxsilr̀ column and gradient elution for the routine determination of podophyllotoxin and six related compounds, epipodophyllotoxin, α‐peltatin, β‐peltatin, 4′‐demethylpodophyllotoxin, podophyllotoxin‐4‐O‐glycoside, and 1,2,3,4‐dehydrodesoxypodophyllotoxin inPodophyllumextracts. The elaborated method gave well resolved peaks for these compounds with good detection response and linearity in t

ISSN:0958-0344    

DOI:10.1002/pca.2800060207

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe cyclic acetals 1b/c were prepared in a biomimetic‐type reactionviathe Mosher‐esters 5a/b of their natural precursor 2,6,10,10‐tetramethyl‐1‐oxaspiro[4.5]dec‐6‐ene‐2,8‐diol (6) which were available from 3,4‐didehydro‐β‐ionone (2) by photosensitized oxidation and subsequent reduction with thiourea. The racemiccis‐diols 3 so‐obtained were esterified with (–)‐α‐methoxy‐α‐trifluoromethyl‐phenylacetyl chloride and the resulting diastereo‐meric esters (4a/b) isolated in pure form (diastereomeric excess>95%) by preparative high performance liquid chromatography. Configuration at C‐6 was determined after bio‐oxidative cleavage of 4a/b to dehydrovomifo‐liols 8a/b. The hemiacetals 5a/b obtained from esters 4a/b by hydrogenation (Pd/BaSO4) were subjected to thermal treatment at pH 3 yielding two optically enriched isomers of Riesling acetal which were subsequently obtained in optically pure form by preparative gas chromatography using a modified cyclodextrin column. Their relative configuration was established by NOE‐experiments. In addition, the structures and the heats of formation of the different diastereomers were calculated using a force field program and the semi‐empirical MNDO, AMI and PM3 methods. The absolute configurations were found from the results of the NOESY experiment, the calculations and the stereoselective synthesis. Riesling acetal enantiomers differed distinctly in their odour properties. (+)‐Riesling acetal 1b showed a weak “woody, fruity, ionone, flowery” note, whereas the (‐)‐isomer 1c exhibited a slight “camphoraceous, flowery” note. Enantiodifferentiation of 1b/c in a number of natural sources with the help of multidimensional gas chromatog

ISSN:0958-0344    

DOI:10.1002/pca.2800060208

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

ISSN:0958-0344    

DOI:10.1002/pca.2800060209

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

ISSN:0958-0344    

DOI:10.1002/pca.2800060210

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

ISSN:0958-0344    

DOI:10.1002/pca.2800060201

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY