Semi-synthetic Chemical Medicines

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7. Example - Anti-cancer medicines

Cancer is often treated with chemotherapy medicines that kill cells undergoing rapid growth (which most cancer cells do). One example of a semi-synthetically derived anti-cancer medicine is irinotecan, which is mainly used to treat colon cancer.

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Figure 1.2 Camptotheca acuminata (source: here)

Irinotecan is produced by chemical modification of camptothecin, a molecule naturally produced by Camptotheca acuminata, called the ‘happy tree’ that is native to China. When researchers discovered camptothecin and tested its potential as a cancer medicine, they observed anti-tumour activity – but also found that the treatment induced unpredictable side effects. Consequently, camptothecin was chemically modified to develop the new medicine irinotecan, which has a more predictable side-effect profile than the naturally occurring molecule. The synthesis of irinotecan from camptothecin requires extensive modification of the chemical structure (Figure 3.3).

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Figure 3.3. Chemical structure of naturally occurring camptothecin and the semi-synthetic irinotecan.