Figure 5.3 The actual degradation made of radio-labelled griseofulvin. A indicates the relative radioactivity at each stage, to show that the labelling is as predicted by the hypothesis

Today acetic acid enriched in 13C would probably be used, which would not require this lengthy degradation. One would look for stronger signals in the 13C NMR spectrum of the product compound for the marked carbon atoms and normal intensity for the unmarked carbon atoms, and also 13C-13C coupling (see later).

The biosynthesis of the compound 2-hydroxy-6-methylacetophenone by the ant Rhytidoponera aciculata has been studied by Tecle, Brophy and Toia, {Insect Biochemistry, 1986, 16, 333) by injecting sodium [2-14C]acetate into mealworm larvae and feeding these to the ants. The radioactive extract of ants was diluted with unlabelled 2-hydroxy-6-methylacetophenone, which was then purified and isolated as its 2,4-dinitrophenylhydrazone, to give a solid with which the radioactivity could be counted. The compound was oxidized with hydrogen peroxide to remove the acetyl group, which removed one unit of radioactivity. The 3-methylcatechol resulting was oxidized by the powerful Kuhn-Roth method which gives acetic acid from methyl groups while the rest of the molecule is oxidized to C02 (Figure 5.4).

Sometimes double or even triple labelling can be useful. Some poner-ine ants have dimethyl disulphide in their mandibular glands. Crewe and Ross {Insect Biochemistry, 1975, 5, 839) used doubly labelled methionine to show that the methyl and sulphur were incorporated together into the dimethyl disulphide by Paltothyreus tarsatus ants (Figure 5.5).

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