The active principles of Cucumis africanus, Cucumis myriocarpus and Cucumis leptodermis have been isolated and examined chemically.
In the case of Cucumis africanus and Cucumis myriocarpus only one poisonous substance was found to which the name "cucumin" has been given since the same substance has been found, so far, in all species of the genus that have been examined. Cucumis leptodermis was found to contain in addition to cucumin a second crystalline toxic principle to which the name "leptodermin" has been given.
Cucumin and leptodermin are chemically very similar. Although differing widely in melting point (cucumin suffers decomposition with constant loss of weight at 110-120° whilst leptodermin melts at 184°) they possess practically the same optical rotatory power, each contain 3 hydroxyl groups and one ketonic group and yield the same product when boiled with dilute acid. They suffer similar decomposition under the action of dilute alkali, three equivalents of alkali being neutralised per molecule. Cucumin and leptodermin are equally toxic towards fish and to rabbits (intravenous route). The M.L.D. in the latter case is ± 2 mgm. per kilo body-weight.
The formula for cucumin has been established as C₂₇H₄₀0₉ and for leptodermin C₂₇H₃₈0₈. They thus differ by H₂0, the elements of water. Preliminary chemical investigations designed to throw light upon the structure of these molecules, shows that cucumin and leptodermin yield complex phenolic substances under suitable conditions.
It is considered likely that certain reactions suggesting a lactone structure can be as satisfactorily explained on the assumption that the acid properties evinced are due to these phenolic groups.
Cucumin is devoid of anthelmintic properties.