Cucurbitacins

Cucurbitacins are tetracyclic terpenes with steroidal structures that are isolated from plants of the family Cucurbitaceae such as pumpkins, gourds, and cucumbers. Ancient peoples used cucurbits medicinally, but they also recognized their toxic properties. Medicinal uses included emetics, narcotics, and antimalarials.

Twenty cucurbitacins have been isolated from the ≈965 known species (in ≈95 genera) of Cucurbitaceae. By the 1950s, the research groups of P. R. Enslin (South African Council for Scientific and Industrial Research, Pretoria) and David Lavie (Weizmann Institute of Science, Rehovot, Israel) had isolated 17 cucurbitacins and studied their properties. Lavie’s group showed that cucurbitacin E (also called α-elaterin) has antitumor properties.

The two most common cucurbitacins are B and E. Cucurbitacin B, whose structure is shown, is extremely toxic when ingested (see hazard information box); E is not as toxic but is still harmful if swallowed.

Cucurbitacins are also known as “bitter principles” of cucurbits. In a recent article, Logan Kistler at the University of Warwick (Coventry, UK), George H. Perry at Penn State (University Park), and colleagues at several other institutions reported that, despite the fruits' bitter taste, prehistoric animals such as mastodons and mammoths ate wild cucurbits and distributed their seeds in their excrement. As the ancient beasts died out, the cucurbits also faded because their primary means of seed dispersal was gone.

Humans came to the rescue. They found that they could eat cucurbit seeds, probably by washing off the bitter constituents. Later, they domesticated squashes and gourds and, by selecting the less bitter seeds, were able to produce more palatable cucurbits. Thus, humans and cucurbits evolved together.