Abstract
If the core of chemistry is making molecules, then the construction of those found in nature—natural products—has long been regarded as one of the highest forms of the art in synthesis. These molecules, produced by living organisms for a variety of purposes, are a key source of pharmaceuticals such as antibiotics and anticancer agents. The medicinal value of natural products has been known for centuries via herbal treatments, and such compounds are still collected, refined and screened for potential drugs today, sometimes being identified from local ‘folk medicine’ practices. By identifying the active ingredients of natural extracts used in traditional medicine, chemists can then synthesize modified forms that may be even more active: this was how the analgesic aspirin was first identified as a derivative of the plant hormone salicylic acid from willow bark. As well as offering such derivatives, natural-product synthesis in organic chemistry can potentially provide a more plentiful alternative source of natural products that are available in only tiny amounts from their natural sources. Efforts to devise cheap and efficient synthetic strategies for molecules such as paclitaxel (Taxol, an anticancer agent present in the Pacific yew) and artemisinin (an anti-malarial extracted from the herb sweet wormwood, qinghao (青蒿), and recognized by the 2015 Nobel Prize for Medicine) are still on-going to satisfy global demand.
Organic synthesis is about much more than making natural products: it contributes, for example, to catalysis, polymer chemistry, food science and the development of wholly synthetic drugs. Yet efforts to make complex natural products may supply a motivational testing ground for developing new synthetic techniques with broader applications. Indeed, many chemists prize the discovery of a new synthetic method above the recreation of some complex natural molecule: it is the means, not the end, that matters.
The field of organic and natural-product synthesis has a strong history in China, where there is a long tradition of herbal medicine. The use of the qinghao extract for treating malaria is first recorded in AD 340, in a manual that the 2015 Nobel laureate Tu Youyou says she consulted for clues about isolating the compound in the beginning of 1970s. Some say that, in the past decade, Chinese natural-product chemistry has entered a ‘golden era’ (Zheng Q-Y and Li A. Sci China Chem 2016;59: 1059–60). Qi-Lin Zhou of Nankai University and Xiaoming Feng of Sichuan University have been at the forefront of this upsurge. Both of them have developed methods for making so-called chiral molecules: arrangements of atoms that have a handedness, so that they can exist in two mirror-image versions. Natural products typically are chiral molecules, and their biological activity may depend on having the correct handedness. The selective synthesis of chiral molecules (asymmetric synthesis) is therefore vital to natural-product chemistry, and typically involves the use of catalysts that are chiral themselves. National Science Review spoke to Zhou and Feng about their work and their perspectives on organic synthesis in China.
Qi-Lin Zhou of College of Chemistry at Nankai University, China. (Courtesy of Q Zhou)
σ-Bond Hydroboration of Cyclopropanes
