Equisarmine, a new steroidal glycoalkaloid, from sterile stems of <i>Equisetum arvense</i>

Glutaminase is an important target that is often over expressed in neurodegenerative and lifestyle related diseases but few effective inhibitors of this enzyme have yet reached clinical trials. To select plants with high glutaminase inhibitory activities, this study was to compare glutaminase inhibitory activities of 20 plant extracts and investigate the isolation, structural elucidation and the inhibitory activity of an active compound from the selected extract of <i>Equisetum arvense</i> L. (horsetail). Equisarmine (<b>1</b>), a new steroidal glycoalkaloid, was elucidated by analyzing its nuclear magnetic resonance (NMR) and electrospray ionization mass spectrometry (ESI-MS) spectral data. The half maximal inhibitory concentration (IC₅₀) values of <b>1</b> and 6-diazo-5-oxo-L-norleucine (DON) as control were 0.72 mM and 0.27 mM, respectively. The results suggest that the extract from horsetail shows the strongest biological activity among 20 tested plant extracts, and that <b>1</b> may serve as a lead compound for the prevention and treatment of neurodegenerative and lifestyle-related diseases by targeting glutaminase. This is the first report on the structure and glutaminase inhibitory activity of <b>1</b>.