Problems and exercisesA Complete Case: the Epothilones
1. Degrees of unsaturation
Epothilone C has the molecular formula C26H39NO5S. Calculate its degrees of unsaturation and distribute them among the groups you know from its structure. How does the result differ from that of epothilone A, C26H39NO6S?
2. Choosing the technique
Say which technique you would use, and why, to settle each question: a) whether the two carbonyls are of the same kind; b) how many methyl groups there are; c) whether the ester is cyclic or open-chain; d) which of the two possible enantiomers is the natural one.
3. Why COSY is not enough
In epothilone B, COSY chains the protons into four loose pieces and no more. Explain why the chain breaks at each of the points where it does, and which experiment allows the pieces to be joined.
4. The resin in the fermenter
Why is an adsorbent resin added to the fermenter instead of extracting the broth at the end? Give three distinct advantages.