Biodiscoveries within the Australian plant genus Eremophila based on international and interdisciplinary collaboration: results and perspectives on outstanding ethical dilemmas

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.

MS/MS-Based Molecular Networking: An Efficient Approach for Natural Products Dereplication

Natural products (NPs) have historically played a primary role in the discovery of small-molecule drugs. However, due to the advent of other methodologies and the drawbacks of NPs, the pharmaceutical industry has largely declined in interest regarding the screening of new drugs from NPs since 2000. There are many technical bottlenecks to quickly obtaining new bioactive NPs on a large scale, which has made NP-based drug discovery very time-consuming, and the first thorny problem faced by researchers is how to dereplicate NPs from crude extracts. Remarkably, with the rapid development of omics, analytical instrumentation, and artificial intelligence technology, in 2012, an efficient approach, known as tandem mass spectrometry (MS/MS)-based molecular networking (MN) analysis, was developed to avoid the rediscovery of known compounds from the complex natural mixtures. Then, in the past decade, based on the classical MN (CLMN), feature-based MN (FBMN), ion identity MN (IIMN), building blocks-based molecular network (BBMN), substructure-based MN (MS2LDA), and bioactivity-based MN (BMN) methods have been presented. In this paper, we review the basic principles, general workflow, and application examples of the methods mentioned above, to further the research and applications of these methods.

Serrulatane diterpenoids with unusual side chain modifications from root bark of Eremophila longifolia

The plant genus Eremophila is endemic to Australia and widespread in arid regions. Root bark extract of Eremophila longifolia (R.Br.) F.Muell. (Scrophulariaceae) was investigated by LC-PDA-HRMS, and dereplication suggested the presence of a series of diterpenoids. Using a combination of preparative- and analytical-scale HPLC separation as well as extensive 1D and 2D NMR analysis, the structures of 12 hitherto unreported serrulatane diterpenoids, eremolongine A-L, were established. These structures included serrulatanes with unusual side chain modifications to form hitherto unseen skeletons with, e.g., cyclopentane, oxepane, and bicyclic hexahydro-1H-cyclopenta[c]furan moieties. Serrulatane diterpenoids in Eremophila have recently been shown to originate from a common biosynthetic precursor with conserved stereochemical configuration, and this was used for tentative assignment of the relative and absolute configuration of the isolated compounds. Triple high-resolution α-glucosidase/α-amylase/PTP1B inhibition profiling demonstrated that several of the eremolongines had weak inhibitory activity towards targets important for management of type 2 diabetes.