Structural Elucidation of Quinovose-Containing Steviol Glycosides from Enzymatic Biotransformation of Stevia rebaudiana

Two steviol glycosides containing quinovose were isolated from a biotransformation mixture of stevia extract derived from <i>Stevia rebaudiana</i> Bertoni leaves. These compounds were elucidated using comprehensive spectroscopic techniques, including nuclear magnetic resonance (NMR) and mass spectrometry (MS). These compounds were designated as Rebaudioside <i>QM</i> and the novel Rebaudioside <i>2QM</i>. Based on structural similarity, we hypothesize that Stevioside <i>E</i> may serve as a biosynthetic precursor for Rebaudioside <i>QM</i>. Comprehensive LC-MS profiling also suggests potential precursors for Rebaudioside <i>2QM</i>. Tentative biosynthetic pathways were proposed for both compounds. The presence of these unknown compounds further supports the notion that <i>S. rebaudiana</i> harbours a wide array of yet-undiscovered steviol glycosides, potentially driven by the inherent diversity of UDP-dependent glycosyltransferases (UGTs) within the plant itself. The discovery of Rebaudioside <i>QM</i> and Rebaudioside <i>2QM</i> expands the known diversity of steviol glycosides and provides new insights into glycosylation patterns in <i>S. rebaudiana</i>, which may support the development and production of novel sweeteners with improved sensory and physicochemical properties.