New diterpenoids isolated from Stevia rebaudiana fermented by Saccharomyces cerevisiae

Five new labdane-type diterpenoids, sterebins Q1 (1), Q2 (2), Q3 (3), Q4 (4), and R (5), were isolated from Stevia rebaudiana fermented by Saccharomyces cerevisiae. The structures of these compounds were established using NMR, MS, and IR methods and their absolute configurations were determined by the ECD spectra of their benzoate derivatives. Through the structures of these new compounds, it was established that the fermentation process caused selective epoxidation and nucleophilic addition of water. Thus, fermentation is an effective way to develop new natural resources for use as drug candidates by enhancing the diversity of natural compounds. (c) 2015 Elsevier Ltd. All rights reserved.