1. Consider the double bonds in the ring of cembrene as drawn in Figure 7.2. How many are cis and how many transi How many possible ring isomers are there for cembrene, presuming there are no stereochemical restrictions?

2. What is the isoprene unit structure of trinervitriol diacetate in Figure 7.3? There is a unique solution.

3. The first cyclized triterpene in plants is cycloartenol. Suggest a way in which the cyclized carbocation formed in the cyclization of squalene ho ho cycloartenol cycloartenol epoxide (Figure 7.6) is converted to cycloartenol. Hint: a different hydrogen atom is eliminated.

4. Suggest a way in which lycopene is cyclized to |3-carotene (a part structure is sufficient).

5. [la-3H]Cholesterol (total activity 160 x 106 cpm) was injected into the larvae of the blowfly Calliphotra stygia. Each larva received 2 jllI of emulsion. Later the pupae which formed were extracted with ethanol, and after purification 20-hydroxyecdysone (activity 30 x 103 cpm) was recovered. What was the specific incorporation of cholesterol into 20-hydroxyecdysone?

6. In another experiment 3p,14a-dihydroxy-5p-[3a-3H]cholest-7-en-6-one (see Figure 7.14 structure A) (28 x 106 cpm) was similarly used with Calliphora stygia larvae. When the pupae were collected 12 h later the activity isolated in 20-hydroxyecdysone was 140,000 cpm. What was the specific incorporation, and does it suggest compound A is an intermediate between cholesterol and 20-hydroxyecdysone?

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