Orthogonal reversed-phase C₁₈ and pentafluorophenyl HPLC separation for phytochemical profiling of serrulatanes in Eremophila denticulata

Serrulatanes constitute a class of unique diterpenoids derived from all-Z nerylneryl diphosphate rather than the conventional all-E diterpenoid precursor geranylgeranyl diphosphate and thus provide an intriguing expansion of the chemical space of plant specialized metabolites. Plants of the Australian Eremophila genus are rich sources of structurally diverse serrulatanes. Here, we report the identification of 15 hitherto undescribed serrulatanes (eremoculatanes A-N), together with 16 previously reported compounds, from the EtOAc extract of Eremophila denticulata leaves. Isolation was performed by a combined use of systematic HPLC-PDA-HRMS-based phytochemical profiling and orthogonal reversed-phase C₁₈ and pentafluorophenyl separations. Among the new compounds isolated, eremoculatane A contains a C₁₂ backbone, for which the configuration was established by comparison of experimentally measured and theoretically calculated ECD spectra. The antihyperglycemic and antibacterial activities of the E. denticulata extract were investigated by high-resolution inhibition profiling, and they indicated that major constituents, mainly serrulatanes and flavonoids, contributed to the observed activity of the extract. One flavonoid, eupafolin (4), displayed moderate α-glucosidase inhibitory activity with an IC₅₀ value of 41.3 μM, and four serrulatanes (8, 9, 19g, and 19j) showed more than 50% PTP1B inhibition at 200 μM.