Pentafluorobenzoyl ester

The quantitative determination by mass spectrometry of 2- and 3-hydroxy fatty acids in complex food matrices and as chemical markers for the detection of endotoxins derived from Gram-negative bacteria requires their transformation into the corresponding methyl esters and, often, the additional derivatization of hydroxyl groups in trimethylsilyl ethers or other derivatives. In a research work on the content of 2- and 3-HSAs in bovine milk, deuterated hydroxy fatty acids have been particularly useful as internal standards for mass analyses. [20] For this study, the methyl ester of 2-HSA-9,10-J2 was prepared from methyl 2-hydroxy-9-cis-octadecenoate by deuteration in the presence of Wilkinson s catalyst. The hydroxy group was transformed into the pentafluorobenzoyl ester and the product was used as standard in gas chromatography with electron-capture negative ion mass spectrometry. 

Although underivatized TDG can be analyzed by GC, the peak shapes are not ideal, and derivatization is required for analysis at concentrations < 1 ppm. Two types of derivative have been used for TDG. The ones most commonly used are silyl ethers, either trimethylsilyl, or tert-butyldimethylsilyl. Pentafluorobenzoyl and heptafluorobutyryl esters have been used for biomedical sample analysis. The conditions are extensively described by Black et al. ... 

Recently, m our laboratories, an improved method for quantitative analysis of amino acids has been developed (Yeung, Baker, and Courts, manuscript in preparation). The carboxylic acid moiety IS derivahzed quantitatively by adding one drop of concentrated HCl to an isobutanol solution of the amino acids, rather than bubbling HCl gas in the conventional manner, prior to heating. Benzoyl chloride is known to be more reactive chemically than acid anhydrides, and pentafluorobenzoyl derivatives are highly sensitive to electron-capture detection (Moffat et al., 1972, Matin and Rowland, 1972, McCallum and Armstrong, 1973 Midha et al., 1979 Cristofoli et al, 1982, Nazarali et al., 1983). Pentafluorobenzoyl chloride (PFBC), therefore, was chosen to derivatize the other reactive groups of the amino acid isobutyl esters. Pentafluorobenzoylation (Fig. 7) was conducted at room temperature in aqueous conditions. 

Most derivatizations for gas chromatography are esterifications or etherifications. For example, analytes containing carboxyl groups are often converted into methyl [156], [161], pentafluorobenzyl [255]-[258], or triethyl esters [259]-[261], Analytes containing acidic hydroxyl groups (phenols, chlorophenols, glycol ethers) or amino groups (e.g.. aniline) can be derivatized with such per-fluorinated compounds as heptafluorobutyric anhydride, pentafluoropropionic anhydride [169], or pentafluorobenzoyl chloride [262]. 

Chromone-3-carboxylic acid esters (34) containing four fluorine atoms on the benzene ring were synthesised by Vorozhtsov, Barkhash, Prudchenko and Khomenko [122, 123] from pentafluorobenzoyl chloride and ethyl acetoacetate in the presence of magnesium ethoxide. During cyclisation, an o-fluorine atom is eliminated the tetrafluorochromone was isolated (in high... 

To detect TDG, TDG sulfoxide, and their acid-labile esters, Black and Read (1991) used TiCla reduction, converting these products into single anal5de TDG. TDG was then converted to its bis(pentafluorobenzoyl) derivative and quantified by GC-MS using negative ion chemical ionization. TDG sulfoxide could also be extracted directly using solid-phase extraction, followed by a Florisil cleanup. Derivatization and quantification was conducted as described previously. TiCls was also used by Daly and O Hehir (2007) to reduce the p-lyase pathway biotransformation product l,l-sulphonylbis[2-(methylsulfinyl)ethane] to l,l -sulfonylbis[2-(methylthio) ethane] (SBMTE). This was followed by automated solid-phase extraction and LC-positive ion-ESI-tandem mass spectrometry. 

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