Irritant diterpene ester toxins were isolated from Euphorbia nubica and E. helioscopia, which are contaminants of the green fodder of livestock in Egypt. Fractionations of
methanol extracts of aerial parts of both plants were monitored by the irritation unit on the mouse ear.
Plant extracts were subjected to multiplicative distribution methods, yielding
irritant hydrophilic fractions that were further purified by column chromatography. Final purification of the materials was achieved by TLC (
silica gel) followed by HPLC, or by TLC alone. In this way, from E. nubica, five Euphorbia factors (Nu1-Nu5) were isolated and characterized as short-chain polyfunctional
diterpene esters of
tigliane-type parent
alcohols. The two weak irritants Nul and Nu3 were triesters of 4-deoxy(4alpha)phorbol. Nu2 was shown to be a triester of the stereoisomeric
tigliane-type parent alcohol 4-deoxyphorbol. Weak
irritant Nu4 probably is a positional isomer of Nu2. Nu5 was characterized as a short-chain triester of 4,20-dideoxy-5xi-hydroxyphorbol. From E. helioscopia, six short- to medium-chain polyfunctional
diterpene esters of the
ingenane type, generally containing unsaturated
acids were obtained, i.e., four
irritant esters of
ingenol (Euphorbia factors H1, H2, H5, and H6) and two
esters of
20-deoxyingenol (non-
irritant Euphorbia substance HS4, and
irritant Euphorbia factor H8). All
irritant Euphorbia factors of the
tigliane and
ingenane diterpene ester type described in this investigation are considered to be more or less active
tumor promoters, i.e., conditional (non-genotoxic) cancerogens. The Euphorbia factors assayed exhibited moderate (H1) to low (H8) relative
tumor-promoting potency in comparison to the
ingenane prototype DTE
tumor promoter 3-TI.