Complex mixtures of natural products

Today, using of the capillary columns can solve many kinds of analytical problems, such as isomer separation and analysis of complex mixtures of natural products and biologicals. 

Gas chromatography, first described by James and Martin in 1952, has become one of the most frequently used separation technique for the analysis of gases, volatile liquids, and solids. The major breakthrough of GC was the introduction of the open mbular column by Golay and Desty in 1958 and the adoption of fused silica capillary columns by Dandeneau and Zerenner in 1979. Today, using of the capillary columns can solve many analytical problems, such as isomeric separation and analysis of complex mixtures of natural products and biological samples. 

Many of these screening systems are not sufficiently robust to handle complex mixtures of natural products from ill-defined biological systems and may be... 

Because of a support-free partition system, HSCCC provides an important advantage over other chromatographic methods by eliminating various complications, such as adsorptive loss and deactivation of samples, as well as contamination from the solid support. As shown by our examples, HSCCC can isolate various components from a complex mixture of natural products by carefully selecting the two-phase solvent system to optimize the partition coefficient (K) of the target component(s). The HSCCC system can also be applied to microanalytical-scale separations without excessive dilution of samples. We believe that HSCCC is an ideal method for the separation and purification of natural products. 

Because of the nature of PCR the identifications can be made either directly from clinical or environmental samples or after culture. However, because environmental samples contain many bacterial species, among which bacilli are the most common, the design of primers is important to avoid complex mixtures of PCR products. Such mixtures are extremely difficult to analyze by direct MS analysis. Furthermore the sensitivity of the analysis may be compromised if the signal is spread among many components. Successful analysis directly from environmental samples therefore is still a topic for current research. 

Terpenes, specifically monoterpenes, are naturally occurring monomers that are usually obtained as by-products of the paper and citms industries. Monoterpenes that are typically employed in hydrocarbon resins are shown in Figure 2. Optically active tf-limonene is obtained from various natural oils, particularly citms oils (81). a and P-pinenes are obtained from sulfate turpentine produced in the kraft (sulfate) pulping process. Southeastern U.S. sulfate turpentine contains approximately 60—70 wt % a-pinene and 20—25 wt % P-pinene (see Terpenoids). Dipentene, which is a complex mixture of if,/-Hmonene, a- and P-pheUandrene, a- and y-terpinene, and terpinolene, is also obtained from the processing of sulfate Hquor (82). 

The nature of the product strongly depends on the length of the hydroxy acid generally when the hydroxyl group is remote the yield of lactone drops significantly. For example, 10-hydroxydecanoic acid [1679-53-4] does not produce any decanoUde instead, the reaction proceeds by intermolecular oligomerization, and a complex mixture of di-, tri-, tetra-, and pentalactones results (90). However, when Pseudomonas sp. or Candida iylindracea]i 2Lses are incubated with 16-hydroxyhexadecanoic acid [506-13-8] hexadecanoUde is the predorninant product (91). 

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the ratio of the analyte is measured versus a... 

An obvious drawback in RCM-based synthesis of unsaturated macrocyclic natural compounds is the lack of control over the newly formed double bond. The products formed are usually obtained as mixture of ( /Z)-isomers with the (E)-isomer dominating in most cases. The best solution for this problem might be a sequence of RCAM followed by (E)- or (Z)-selective partial reduction. Until now, alkyne metathesis has remained in the shadow of alkene-based metathesis reactions. One of the reasons maybe the lack of commercially available catalysts for this type of reaction. When alkyne metathesis as a new synthetic tool was reviewed in early 1999 [184], there existed only a single report disclosed by Fiirstner s laboratory [185] on the RCAM-based conversion of functionalized diynes to triple-bonded 12- to 28-membered macrocycles with the concomitant expulsion of 2-butyne (cf Fig. 3a). These reactions were catalyzed by Schrock s tungsten-carbyne complex G. Since then, Furstner and coworkers have achieved a series of natural product syntheses, which seem to establish RCAM followed by partial reduction to (Z)- or (E)-cycloalkenes as a useful macrocyclization alternative to RCM. As work up to early 2000, including the development of alternative alkyne metathesis catalysts, is competently covered in Fiirstner s excellent review [2a], we will concentrate here only on the most recent natural product syntheses, which were all achieved by Fiirstner s team. 

The treatment of sucrose with anhydrous HF89 results in the formation of a complex mixture of pseudooligo- and poly-saccharides up to dp 14, which were detected by fast-atom-bombardment mass spectrometry (FABMS). Some of the smaller products were isolated and identified by comparison with the known compounds prepared86 88 a-D-Fru/-1,2 2,1 -p-D-Fru/j (1), either free or variously glucosylated, was a major product, and this is in accord with the known stability of the compound. The mechanism of formation of the products in the case of sucrose involves preliminary condensation of two fructose residues. The resultant dianhydride is then glucosylated by glucopyranosyl cation.89 The characterization of this type of compound was an important step because it has permitted an increased understanding of the chemical nature of caramels. 

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