Derivatization during development

Dehydrocorticosterone 221 Demeton-S-methyl 362 Demeton-S-methylsulfone 362 Deoxynivalenol 89,147,148 Derivatization, aims 56, 57 -, during development 57 -, for clean up 56 -, in situ 56... 

Reactions can also occur during chromatographic development. These can either be undesired reactions or planned derivatizations. Thus, Weicker and Brossmer [11] have reported, for example, that hexoses, pentoses and disaccharides can be ammated when ammonia-containing mobile phases are employed on silica gel G layers. On the other hand, fluorescamine or ninhydrin have been added to the... 

The algorithm described above is for a three-step combinatorial synthesis. However, the method is not limited to only three-step combinatorial libraries the solid-phase support can be derivatized before the directed split-and-pool synthesis on the Encore synthesizer. The necklace coding can also be a very useful tool during the chemistry development process. 

Phenols are important industrial chemicals, for example, in the production of various plastics and resins, and may leach into surface and ground waters either during production or from the discharged products at landfill sites. Because of their ecological importance and their widespread use, methods for phenols and related compounds (e.g., anilines) were developed already at an early stage. Many of these methods rely on GC (or GC/MS), which normally requires derivatization prior to GC analysis. Standard methods for the derivatization of phenols are silylation, methylation, or acetylation.5 The last mentioned has the advantage that it can be carried out in the aqueous sample directly. The deriva-tized phenols can thus be extracted more easily and with a higher yield from the aqueous sample by... 

Pyridine or another solvent with a large solvation capacity (acetonitrile, dimethyl-formamide) are mostly used as solvents in the silylation reactions. Pyridine provides on some phases a broad tailing peak and can overlap lower components. Lehrfeld [85] therefore developed a procedure for the removal of pyridine from the sample before the analysis. During the derivatization anhydrous conditions are essential because the derivatives are decomposed by traces of water. However, a method has been described for the preparation of silyl derivatives even in the presence of water its principle consists in the addition of such a large excess of the silylating agent that all of the water present is removed [86]. This can be of importance in the treatment of samples that cannot be previously dried as losses of more volatile components could occur. The extent to which the presence of water affects the reaction yield and whether or not a large excess of by-products has an adverse effect must be tested, however. 

From these and other studies we have developed a rule of thumb for prediction of stereochemical induction during enolate derivatization for both syn and anti substrates, the relative stereochemistry at the newly created asymmetric center is opposite to that of the sulfoxide moiety when the structure is drawn as shown above. 

---