Singlet oxygen-mediated synthesis of malarial chemotherapeutic agents

Malaria is the leading infectious disease found in humans, affecting third-world countries. Worldwide, more than two billion people are at risk of malaria, with about 500 million clinical cases of malaria each year and one million deaths. In this focused review, an effort has been made to summarize the reactions of singlet oxygen with organic substrates, their stereoselectivity, stereospecificity and utilization in generating dioxetanes and endoperoxides. The study of production and reactivity indications of this exceptional molecule has emerged as a rich and diverse area in the synthesis of antimalarials like artemisinin and its semisynthetic derivatives, structurally simple 1,2,4-trioxanes, sesquiterpene isonitriles, synthetic cyclic, and other acyclic peroxides. Artermisinin, a mainstay in antimalarial drug therapy, meets the dual challenge posed by drug-resistant parasites and rapid advancement of lethal malarial threat. The cardinal mechanism of peroxidation and ring closure in its production are induced by singlet oxygen and acid. Moreover, its complex structure restricts the complete chemical synthesis of artemisinin. Consequently, the limited availability coupled with increasing demand for artemisinin has paved the way for the preparation of synthetic alternatives of artemisinin and its derivatives. Likewise, past evidence of the structure-activity relationship indicate the importance of singlet oxygen in antimalarial drug synthesis. It is anticipated that this compendium on the chemistry of singlet oxygen will be of use to organic/medicinal chemists and pharmacologists working on antimalarial drug development.