The story
In the late 1960s, a Chinese research programme known as Project 523 set out to find new malaria drugs. Tu Youyou and her team went through old medical texts and tested plant extracts. A text from the fourth century pointed to sweet wormwood, and, by Tu's account, to soaking the herb instead of boiling it. A low-temperature extraction worked where hot extraction had failed.
In 1972 her team isolated the active compound, now called artemisinin. Tu received the 2015 Nobel Prize in Physiology or Medicine, sharing it with William Campbell and Satoshi Omura.
Artemisinin has an unusual feature: a peroxide bridge, an O-O bond, inside a cage of rings. Drugs rarely contain peroxides because they are reactive. Here the bridge is essential, and without it the activity is lost. It is thought to be broken by iron from the heme that the parasite releases when it digests haemoglobin, producing reactive species that damage the parasite.
Artemisinin leaves the body quickly, so it is used today as derivatives such as artesunate and artemether, combined with a longer-acting partner drug. The World Health Organization recommends these combinations as first-line treatment for falciparum malaria.
What to look for in the 3D view
Look for the pair of red oxygen atoms bonded to each other near the middle of the cage. That O-O bond is the peroxide bridge. It is one bond long, and it is the whole mechanism. Notice also that there is no nitrogen anywhere in the molecule, and that it is a compact, rigid cage rather than a long chain.
