Euphorbia species were widely used in traditional medicines for the treatment of several diseases. From the aerial parts of Egyptian endemic plant, Euphorbia sanctae-catharinae, three new premyrsinane diterpenoids, namely, euphosantianane E−G (1−3), alongside four known triterpenes, 9,19-cyclolanostane-3β,24S-diol (4), 25-methoxycycloartane-3β,24S-diol (5), 25-methylenecycloartan-3β,24R-diol (6), and 25-methylenecycloartan-3β,24S-diol (7), were isolated and identified. The chemical structures were proven depending upon spectroscopic analysis, including FTIR, HRFABMS, and 1D/2D-NMR. The chemotaxonomic significance of the isolated compounds, especially diterpenes from E. sanctae-catharinae compared to those documented from different Euphorbia species was also studied via agglomerative hierarchical clustering (AHC). The Egyptian endemic Euphorbia sanctae-catharina was grouped with E. bupleuroides, E. fidjiana, E. fischeriana, E. pithyusa subsp. cupanii, E. prolifera, and E. seguieriana, where myrsinol diterpenoids were the characteristic compounds.
