What compound does Artemisia annua produce that is used against malaria?

Artemisia annua, commonly known as sweet wormwood, is known for producing artemisinin, a compound that has been pivotal in the treatment of malaria. This sesquiterpene lactone has demonstrated significant antimalarial properties, particularly against Plasmodium falciparum, the most deadly species of malaria-causing parasites.

Artemisinin works by generating free radicals when it interacts with iron found in the malaria parasite’s cells, leading to damage of the parasite's membranes and ultimately its death. This mechanism is what has made artemisinin-based therapies, like artemisinin combination therapies (ACTs), effective for treating malaria in both uncomplicated and severe forms.

In contrast, the other compounds listed don't have the same established connection to malaria treatment. Colchicine is used primarily for gout and certain other conditions but not for malaria. Coumarin is a compound found in many plants and used in various applications, but it does not possess the antimalarial properties associated with artemisinin. Allicin, derived from garlic, is noted for its antimicrobial and health benefits but is unrelated to malaria treatment. Thus, artemisinin is uniquely recognized for its direct role in combating malaria, establishing it as the correct answer.