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A frequently studied environmental contaminant is the active substance diclofenac, which is removed insufficiently in sewage treatment plants. Since its inclusion in the watch list of the EU Water Framework Directive, the concentrations in surface waters will be determined throughout Europe. For this, still, more precise analytical methods are needed. As a reference, HPLC-MS is frequently employed. One of the major metabolites is 4’-hydroxydiclofenac (4’-OH-DCF). Also, diclofenac lactam is important for assessing degradation and transformation. Aceclofenac (ACF), the glycolic acid ester of diclofenac is used as a drug, too, and could potentially be cleaved to yield diclofenac again. In various sewage treatment plant influent samples, diclofenac, 4’-OH-DCF, DCF lactam and ACF could be determined with detection limits of 3 µg/L, 0.2 µg/L, 0.17 µg/L and 10 ng/L, respectively.
For many heterogeneous sensor applications as well as the synthesis of hapten antigens to produce antibodies, protein conjugates of the target substance are essential. A requirement is that the target substance already offers or is modified to contain a functionality that allows for coupling to a protein, that is, an amino acid residue. Ideally, to avoid shielding of the compound by the carrier protein, a sufficient distance to the protein surface should be provided. With its carboxyl function diclofenac (DCF) allows for direct binding to lysine residues after in situ synthesis of the NHS ester. One problem is that diclofenac as free acid tends to autocondensation, which results in low yields. Here we describe the 'insertion' of a C6 spacer via synthesis of the amide with 6-aminohexanoic acid. To carry out the reaction in solution, first the methyl ester of the amino acid had to be produced. Due to otherwise low yields and large cleaning efforts, solid-phase synthesis on Fmoc Ahx Wang resin is recommended. The crude product is mainly contaminated by cleavage products from the resin which were removed by chromatography. The structure of the highly pure hapten was completely determined by nuclear magnetic resonance (NMR) spectroscopy.