Derivatisation alkylation

Transformation of bromocriptine free base 2 into water soluble salt -mesylate, is the only way to obtain a suitable therapeutical form. Crystallization of mesylate using alcohol as a solvent in the presence of excess of strong acid, e.g. methanesulphonic acid can induce formation of 12 -0-alkyl-derivative 2. Until now this derivatisation of ergot molecule has been practically unknown. In continuation we developed the preparative method for obtaining these compounds, (using tetrafluoroboric acid as a catalyst) (ref. 20). 

The hydrosi(ly)lations of alkenes and alkynes are very important catalytic processes for the synthesis of alkyl- and alkenyl-silanes, respectively, which can be further transformed into aldehydes, ketones or alcohols by estabhshed stoichiometric organic transformations, or used as nucleophiles in cross-coupling reactions. Hydrosilylation is also used for the derivatisation of Si containing polymers. The drawbacks of the most widespread hydrosilylation catalysts [the Speier s system, H PtCl/PrOH, and Karstedt s complex [Pt2(divinyl-disiloxane)3] include the formation of side-products, in addition to the desired anh-Markovnikov Si-H addition product. In the hydrosilylation of alkynes, formation of di-silanes (by competing further reaction of the product alkenyl-silane) and of geometrical isomers (a-isomer from the Markovnikov addition and Z-p and -P from the anh-Markovnikov addition. Scheme 2.6) are also possible. 

Another way for covalent immobilisation is to synthesise indicator chemistry with polymerizable entities such as methacrylate groups (Figure 4). These groups can then be copolymerized with monomers such as hydrophobic methyl methacrylate or hydrophilic acryl amide to give sensor copolymers. In order to obtain self-plasticized materials, methacrylate monomers with long alkyl chains (hexyl or dodecyl methacrylate) can be used. Thus, sensor copolymers are obtained which have a Tg below room temperature. Similarly, ionophores and ionic additives (quaternary ammonium ions and borates) can be derivatised to give methacrylate derivatives. 

A potentially more sensitive and selective approach involves reaction of formic acid with a reagent to form a chromophore or fluorophore, followed by chromatographic analysis. A wide variety of alkylating and silylating reagents have been used for this purpose. Two serious drawbacks to this approach are that inorganic salts and/or water interfere with the derivatisation reaction, and these reactions are generally not specific for formic acid or other carboxylic acids. These techniques are prone to errors from adsorption losses, contamination, and decomposition of the components of interest. Enzymic techniques, in contrast, are ideal for the analysis of non-saline water samples, since they are compatible with aqueous media and involve little or no chemical or physical alterations of the sample (e.g., pH, temperature). 

Alkyl halides, alkyl sulfonates and other alkylating agents have also been subject to scmtiny in spheres other than pharmaceuticals, such as in environmental analysis. Various approaches have included two-step SPE, derivatisation with trifluoroacetic anhydride followed by GC/MS (for cyclophosphamide and its analogues in sewage water) SPE on surface water to isolate the antineoplastic agents carmustine, chlorambucil, cyclophosphamide and melphalan for LC-UV and LC-fluorescence measurements and derivatisation of alkyl halides and epoxides with 4-nitrothiophenol followed by HPLC-UV detection (claimed to be better than NBP derivatisation). A patent exists for a field test kit for mustard gases in military use based on NBP derivatisation. 

A-nitrosomethylurea and other carcinogens Food products incubated with nitrite under simulated gastric conditions Column chromatography NBP derivatisation Photometric Measuring alkylating activity [10]... 

The metabolites are then simultaneously eluted from the disk and derivatised to their ethyl esters by adding 100 jtl of ethyl iodide and heating the vial at 100 °C for one hour. Using this approach, only a single sample is analysed, and because the disk-catalysed alkylation reaction does not transesterify Dacthal, the speciation of Dacthal is maintained. In addition, no sample clean-up steps are required, and only a total of 5 ml of nonchlorinated organic solvent is used. 

Blais et al. [12] has described a method using HPLC coupled with AAS for the determination of ionic alkyl lead compounds in soils. They demonstrated that previously published methods gave poor recoveries of lead and the formation of artifacts during the isolation and derivatisation procedures. An alternative procedure is described involving a series of selective extractions... 

Consequently, the mixture of hydroxyknotanes was used for the alkylation and only the resulting mixtures of dendroknots were later resolved on HPLC. The difficulty can be overcome by selecting a better protecting group whose expected reactivity will neither affect the amide-knotane synthesis nor its further derivatisation. 4-allyloxypyridine 2,6-dicarboxytic acid dichloride seemed to be a suitable protected... 

Cold-trapping has been used successfully for the determination of alkyl-Sn and Se compounds, Pb and some As compounds (Donard, 1987). The technique presents the advantages of both concentrating the species and sequentially separating them according to their specific volatility. One drawback of this method is that only volatile forms of elements (hydrides, ethylated or methylated forms) may be separated, requiring a derivatisation step other molecules of low... 

---