Identification of PTP1B and α-Glucosidase Inhibitory Serrulatanes from Eremophila spp. by Combined use of Dual High-Resolution PTP1B and α-Glucosidase Inhibition Profiling and HPLC-HRMS-SPE-NMR

According to the International Diabetes Federation, type 2 diabetes (T2D) has reached epidemic proportions, affecting more than 382 million people worldwide. Inhibition of protein tyrosine phosphatase-1B (PTP1B) and α-glucosidase is a recognized therapeutic approach for management of T2D and its associated complications. The lack of clinical drugs targeting PTP1B and side effects of the existing α-glucosidase drugs, emphasize the need for new drug leads for these T2D targets. In the present work, dual high-resolution PTP1B and α-glucosidase inhibition profiles of Eremophila gibbosa, E. glabra, and E. aff. drummondii "Kalgoorlie" were used for pinpointing α-glucosidase and/or PTP1B inhibitory constituents directly from the crude extracts. A subsequent targeted high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy (HPLC-HRMS-SPE-NMR) analysis and preparative-scale HPLC isolation led to identification of 21 metabolites from the three species, of which 16 were serrulatane-type diterpenoids (12 new) associated with either α-glucosidase and/or PTP1B inhibition. This is the first report of serrulatane-type diterpenoids as potential α-glucosidase and/or PTP1B inhibitors.

The genus Eremophila (Scrophulariaceae): an ethnobotanical, biological and phytochemical review

Objectives

Eremophila (Scrophulariaceae) is an endemic Australian genus with 214 species, which is commonly known as Fuchsia bush, Emu bush or Poverty bush. Plants of this genus played an important role for the Australian Aborigines who used them widely for medicinal and ceremonial purposes. Many studies have been carried out on many species of this genus and have generated immense data about the chemical composition and corresponding biological activity of extracts and isolated secondary metabolites.

Key findings

Thorough phytochemical investigations of different Eremophila species have resulted in the isolation of more than 200 secondary metabolites of different classes with diterpenes as major constituents. Biological studies and traditional clinical practice demonstrated that Eremophila and its bioactive compounds possess various pharmacological properties. Plants were employed especially as a cardiotonic drug and also as potent anti-inflammatory, antimicrobial and antiviral agents.

Summary

Further investigations are required to explore other Eremophila species, to evaluate the different biological activities of either their extracts or the isolated compounds and the possible underlying modes of action.

Antimicrobial compounds from the Australian desert plant Eremophila neglecta

A crude extract from the Australian desert plant Eremophila neglecta has recently been shown to possess antibacterial activity in a survey of candidate plants that may bear novel antimicrobial compounds. Bioassay-directed fractionation of the Et(2)O extract of E. neglecta using a broth microdilution assay led to the isolation of three new serrulatane-type diterpenoids, 2,19-diacetoxy-8-hydroxyserrulat-14-ene (2), 8,19-dihydroxyserrulat-14-ene (3), and 8-hydroxyserrulat-14-en-19-oic acid (4), and a known o-naphthoquinone commonly referred to as biflorin (5). The structures of 2-5 were determined using 1D and 2D NMR, FTIR, and high-resolution mass spectrometry. Compounds 3-5 showed antimicrobial activity against Gram-positive bacteria including Staphylococcus aureus, Streptococcus pyogenes, and S. pneumoniae. The minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) ranged from 6.5 to 101.6 microM and 12.7 to 202.9 microM, respectively. No activity was observed for these compounds against Gram-negative bacteria.

Bactericidal and cyclooxygenase inhibitory diterpenes from Eremophila sturtii

Two serrulatane diterpenes, 3,8-dihydroxyserrulatic acid (1) and serrulatic acid (2), have been isolated from Eremophila sturtii through bioassay-guided fractionation. These compounds inhibit the inflammation pathway enzymes cyclooxygenase 1 and 2, and exhibit bactericidal activity against Staphylococcus aureus.

An approach to serrulatane diterpenes via endo-selective conjugate nucleophilic addition to arene-Cr(CO)3 complexes

[formula: see text] Starting from a nonracemic planar-chiral arene tricarbonyl chromium complex, the serrulatane diterpenoid (+)-20-methoxy-serrulat-14-en-7,8-diol was synthesized in a highly stereoselective fashion. The key step of the synthesis is an endo-selective conjugate nucleophilic addition of lithio-methylphenyl sulfone to a 1-ethylidene-tetralin-Cr(CO)3 derivative. By employing different substrates and nucleophiles it was shown that the surprising and rather general endo selectivity must result from a unique complex induced proximity effect under participation of the Cr(CO)3 moiety.

The phytochemistry of the Myoporaceae

The secondary metabolites isolated from members of the Myoporaceae are reviewed. More than 200 compounds, whose structures have been elucidated, are listed together with their source in the Appendix.