Indirect synthesis techniques

Because natural samples often have background levels of organic material and the chemical substrate concentration is low, indirect measurement techniques can not be used and 14C, other radiolabelled techniques, or sensitive specific analytical methods are required. If radiolabelled methods are used, the cost of the method increases, due to the cost of synthesis of the radiolabelled material. Use of radiolabelled chemicals is required for registration studies on environmental fate testing of pesticides. 

Electroorganic Synthesis by Indirect Electrochemical Methods New Applications of Electrochemical Techniques ... 

Chiral separation of drng molecules and of their precursors, in the case of synthesis of enantiomerically pure drugs, is one of the important application areas of HPLC in pharmaceutical analysis. Besides HPLC, capillary electrophoresis (CE) is another technique of choice for chiral separations. Chapter 18 provides an overview of the different modes (e.g., direct and indirect ones) of obtaining a chiral separation in HPLC and CE. The direct approaches, i.e., those where the compound of interest is not derivatized prior to separation, are discussed in more detail since they are cnrrently the most frequently used techniques. These approaches require the use of the so-called chiral selectors to enable enantioselective recognition and enantiomeric separation. Many different molecnles have been nsed as chiral selectors, both in HPLC and CE. They can be classified into three different groups, based on their... 

The reactions of transient silylenes are so rapid that most of the limited mechanistic information that has been obtained over the past quarter-century has been through indirect means. Direct measurements of silylene reaction rates by kinetic spectroscopy in the past decade have yielded important new insights. One can predict with some confidence an explosion of mechanistic studies of silylenes employing fast spectroscopies capable of providing more structural information than traditional electronic absorption and emission techniques. The nearly universal reversibility of silylene reactions remains to be fully exploited through kinetic studies of retro-reactions. The mechanisms of most silylene reactions remain to be fully elucidated, and this task will increase in urgency as silylenes see more use in synthesis. 

Direct synthesis of metal-substituted zeolites has long been sought. However, since the post-synthesis modifications can be made under wide-ranging conditions (temperature, solvent, atmosphere, pH, etc.) far from those for the zeolite synthesis, the modifications of zeolites present us with powerful indirect methods for manipulating the properties of zeolites. Therefore, the fine-tuning of the properties of zeolites will continue to be achieved by developing various post-synthesis modification procedures as well as direct synthetic techniques. 

The first section will be devoted to the synthesis of these libraries using the so-called mix-and-split or divide-and-recombine approach (2, 3) and to their analytical characterization. The following sections will focus on different methods to determine the structure of an active component from an SP pool library direct structure determination (Section 7.2) and indirect structure determination, via deconvolutive methods (Section 7.3) or encoding methods (Section 7.4), will be covered. Finally, a section will be devoted to new trends in SP pool libraries, paying particular attention to innovative methods for the fast and reliable discovery of new active structures through miniaturization (bead-based techniques). 

Besides the group of psychotropic compounds, we must quote here the antibiotics as drugs where a rapid recent development of techniques can be observed. D.c. polarographic techniques for the determination of chloramphenicol [242], tetracycline [243] and streptomycin [244] are available. The polarographic determination of penicillin G potassium salt is only indirect and is preceded by the introduction of a nitroso group [245]. The synthesis of chloramphenicol comprises the chemical reduc-... 

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