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.1.3).Typically, absolute amounts of asterosaponinmixtures of about 500 "g 1 mg are injected onto the column.5.1.2.3 NMR STRUCTURAL INFORMATIONFigure 5.1.4 shows examples of what kind of structural information can beobtained from such an LC NMR MS run.This figure shows the NMR chro-matogram of a total asterosaponin fraction obtained from MSPD extraction.For clarity, the regions of the methyl and olefinic/anomeric resonances areshown.As a complete structural elucidation of complex glycosidic compounds1cannot be achieved by one-dimensional H NMR spectra, which are providedby on-flow LC NMR (13C NMR data are still required for an unambiguousassignment of resonances), two approaches have proven to be effective in thecase of asterosaponins in order to identify new compounds for a subsequentsemi-preparative isolation: LC NMR/LC NMR MS Applications to Natural Products Analysis 1175g Animal material+ 20 ml H2O+ 9 g RP-18Bed of 9 g RP-18Wash: 100 ml H2OElute: 2 10 ml H2O2 10 ml CH3CN/H2O (10:90)1 2 3 4 5 6 7 8 9 1011 12 13 141516 2 10 ml CH3CN/H2O (20:80)2 10 ml CH3CN/H2O (30:70)Asterosaponins in fraction 11 (11 mg)LC-NMR-MS1 mg injected into LC NMR MS systemFigure 5.1.2 Matrix solid-phase dispersion (MSPD) extraction as a micro-preparative ex-traction technique for an on-flow LC NMR MS screening.Since the latter requires onlysample amounts in the 0.5 2 mg range, the sample preparation can be achieved by fast small-scale extraction procedures, such as MSPD.This is a sample preparation technique thatcombines both sample homogenisation and extraction of compounds of interest in one singlestep starting from the intact sample material.Thus, it simplifies the extraction and clean-upsteps, reduces the sample manipulation and is much faster than conventional techniques.It istherefore very well suited for a rough separation of extracts into classes of compounds ofsimilar polarities, which can then be submitted to LC NMR MS analysis1.The analysis of easy-to-assign resonances characteristic of certain structuralfeatures ( e.g.olefinic protons, methyl groups or anomeric protons of sugar units).A good example of this category is the study of the resonances of the steroidalH3-18 methyl groups.Most asterosaponins possess a hydroxy function at C-20.The corresponding H3-18 methyl group resonates at ca.7 ppm (see Figure5.1.4, dotted frames).The significant upfield shift of this resonance in rubero-sides A, B and G clearly indicates a lack of this C-20 hydroxy function in theproximity of H3-18.The resonances of the actual H3-21 methyl group corrobor-ate this assignment: in asterosaponins with a C-20 OH group, a singlet at about 118 LC NMR and Related TechniquesHPLC unitUV detectorPeak samplingunit (BPSU)20:1Flow splitterSyringe pumpNMRspectrometerMassspectrometerEsquire LCMS/MSFigure 5.1.3 Schematic of an LC NMR MS set-up1.25 ppm appears, while in those without one a doublet between 0.8 and0.9 ppm appears.However, the H3-21 methyl resonances sometimes overlapwith other signals.A further example is the ready assignment of an olefinic resonance whichappears in the spectrum of ruberoside G in addition to the H-11 signal at5.3 ppm, common to asterosaponins.Its low-field chemical shift of 6.2 ppm(solid frame in Figure 5.1.4, and Figure 5.1.5) indicates the presence of a doublebond in the steroidal side-chain in proximity to a deshielding functional groupsuch as a carbonyl.2.The comparison of sub-spectra of unknowns with those of known compounds orwith those of other unknowns in order to recognise structural analogies or differ- Solid frame: olefinic resonance Dashed frames: identical Dashed-dotted frames: identical Dotted frames: upfield shift of the CH3-18 methylat 6.2 ppm indicates a double bond sugar methyl resonances side-chain methyl resonances resonances suggest the absence of a hydroxyin the side-chain in the vicinity of a function at C-20Abund.1253.7 6: MS, T ime=399.5m in ( #9 , 100% =15006a35) rb100Ruberoside Bcarbonyl function 80604020 1270.611 7 1179.1 1194.4 1233.8 1293.7 1316.7 1333354.01150 117 1200 122 1250 1275 1300 1325 m/z5 5Abund.1243.7 5: MS, T ime=373.7m in (#868) , 10 =19276arb0%10022 24 2780sec sec6018 20 23 25 40500 50012 20 1225.611 2 1167.4 1195.7 1277.8 1310.2 1327.7 1350.250
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Tematy
IndexLucas Derks Techniki NLP W Tworzeniu Dobrych Zwišzków Z LudŸmi
Nizinski Stanislaw Informatyczne systemy zarzadzania eksploatacja obiektow technicznych
Lewandowski Artur Kod umysłu (techniki sprzedaży)
Zarzšdzanie eksploatacjš obiektów technicznych Żółtowski Niziński
Andrew Stark Drawing the Line, Public and Private in America (2009)
techniki negocjacji (21 stron)
Christopher G Nuttall [The Em The Thin Blue Line (epub)
allianz ubezpieczenia techniczne
Chris Ewan Dead Line (epub)
Przykladowe sprawozdanie finansowe on line