Questions

1. Leaves of Nerium oleander were injected with sodium [2-2H3]acetate. Aphis nerii were allowed to feed on the leaves and then the aphids were fed to the ladybirds Coccinella undecimpunctata. The cardiac glycoside oleandrin was isolated from the ladybirds and subjected to mass spectrometry. There was a small, but distinct mass spectral peak at M+3. What do you conclude?

2. What experiment do you suggest to discover whether pyrrolizidine alkaloids are reduced from the N-oxide form of the plants to the free base in the gut of an insect and later re-oxidized?

3. By NMR spectrometry, how would you check that the labelling of valine in Figure 10.9 had remained intact in linamarin?

4. In a study of the conversion of phenylalanine to mandelonitrile, benzaldehyde and HCN, DL-phenylalanine (0.17 ^moles) labelled with 14C in the phenyl ring (specific activity 82 jnCi mmoL1) was injected into each of 10 individual millipedes. The specific activity of the benzaldehyde isolated from all ten at the end of the experiment was 7.39 x 10"6 \iCi mmol-1. Allowance must be made for the dilution with endogenous precursors, because 2.3 jimoles of benzaldehyde was isolated while only 0.17 jimoles of phenylalanine was injected. Presuming that only the radioactivity in L-phenylalanine is used for incorporation, what was the %age conversion of radio-labelled phenylalanine to benzaldehyde? No radioactivity was found in the HCN.

5. The secretion of the grasshopper Romalea microptera contains, in addition to romallenone (Figure 10.18) verbenone, isophorone and 2,6,6-trimethylcyclohex-2-en-l,4-dione, below. What is the likely source of these compounds?

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