1. Show two possible polyketides that could give rise to emodin (Figure 8.16).

2. Show a common biosynthetic route that accounts for m-propylphenol and mellein (Figure 8.10).

3. Suggest biosynthetic precursors for the two aromatic compounds in the queen substance of honeybees, methyl ^-hydroxybenzoate and 4-hydroxy-3-methoxyphenylethanol (Figure 3.32).

4. What kind of experiment would you suggest to decide whether the plant compound eugenin was derived by the polyketide route or the shikimic acid route?

5. Marginalin is a yellow pigment in the pygidial glands of the water beetle Dytiscus marginalis. Also present are /7-hydroxybenzaldehyde and homogentisic acid (Figure 8.11). Suggest biosynthetic origins for all three.

oh o eugenin oh o eugenin marginalin marginalin

6. The pterins are shown in their amide forms, because these are the more stable tautomers. Below is the violet-blue pterorhodin in its amide form, draw it in its fully aromatic imidol form.

nh2 nh2

nh2 nh2

pterorhodin pterorhodin

7. The enzyme tyrosine phenol lyase can convert tyrosine to phenol and phenol back to tyrosine. Working on tyrosine, it also produces pyruvic acid and ammonia. The tyrosine is attached to pyridoxal phosphate during the reaction, and the phenol goes through a quinonoid form. Write the reaction going either from tyrosine or from phenol. This route may be a way by which insects can de-toxify phenol they themselves have produced.

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