Preparative-scale chromatography high-pressure

Concerning the synthetic applications, it is clear that these reactions have allowed the obtaining of new structures and are useful for the synthesis of many polyfunctional molecules not easily obtainable by more classical ways. Moreover, starting materials are nearly always very simple and often commercially available. One limitation should be perhaps in some cases — the separation of formed products. However now, low- and high-pressure preparative liquid chromatographies become more and more usual in laboratories. Those techniques allow work on a large scale and are no more difficult to handle than other usual methods. Thus these techniques improve the interest of our reactions which lead to elaborate structures from trivial starting molecules. 

Figure 11.5. Schematic diagram of continuous compression columns for high-pressure Preparative-scale liquid chromatography. The arrows represent the force directions. A = radial compression, B = dynamic axial compression, and C = annular expansion.

As the last physical method useful for stereochemical studies of carotenoids one should mention high pressure liquid chromatography. This was first applied to the carotenoid field in 1971 by Stewart and Wheaton 159) and subsequently shown to be superior for separation of geometrical isomers (75, 76, 158) and diastereomers (46, 75). Future developments on a preparative scale are anticipated. 

High Pressure Liquid Chromatography.—Reverse phase h.p.l.c. using octadecyl bonded groups has been developed for the rapid and efficient separation of nucleosides, nucleotides, and protected oligonucleotides on both analytical and preparative scales. ... 

The synthesis of 6-hydroxy fluvastatin with M. rammaniana DSM 62752 gave high conversion (>95 %) in shake flask culture on 400 mL scale with 0.1 g L of fluvastatin as well as on 22 L scale in a Wave bioreactor-fed batch process at a final substrate concentration of 0.4 g L Instead of the partial purification by a second solid-phase extraction described above, 6-hydroxy fluvastatin can be obtained in high purity ( 95 %) by, for example, preparative medium-pressure liquid chromatography (MPLC) on RP18 silica gel. ... 

High-performance liquid chromatography does similar things with more sophisticated instrumentation. It can separate closely related chemical compounds on a research scale or on a preparative scale liquid solvents, or mixtures of several solvents under positive pressure, replace the "carrier gas" of Fig. 11.3. The solid support must have small particle sizes (3- to 10-pm diameter), so that relatively high pressures can be sustained throughout the column, and it is at the interface between the liquid eluant and the solid particles that the chromatographic separation is accomplished. 

High performance and low pressure liquid chromatography (adsorption) Separation of lipid classes, separation of lipids by molecular weight and degree of unsaturation Impractical for most preparative or large-scale processes... 

Cyclone separators can be effective as collection devices in SFC. However, they tend to be best suited for semipermanent applications, like preparative-scale chromatography. They are not user friendly for the separation of a large number of different samples in a short time. Each fraction requires a separate cyclone separator. For modest scale separations, the cyclone separators are bulky, with a very large internal surface area, which is difficult to clean out. Because they are subjected to relatively high pressures, they are usually made of stainless steel. Connections are usually made with large-diameter stainless-steel tubing and the whole apparatus is bolted to some sort of rack mount. One could think of this approaches a scaled-down pilot plant. 

Fig. 5-2) Column B of Fig. 13-2 is useful for preparative scale separations, while column C is intended for routine analytical separations (see Section 13-2C). High efficiency separations, which require long columns, high pressures, and semiautomated equipment, are best carried out in metal columns. For a further discussion of the columns used in adsorption chromatography, see Ref. (/). 

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