A minor product, rebaudioside M2 (2), from the bioconversion reaction of rebaudioside A (4) to rebaudioside D (3), was isolated and the complete structure of the novel steviol glycoside was determined. Rebaudioside M2 (2) is considered an isomer of rebaudioside M (1) and contains a relatively rare 1→6 sugar linkage. It was isolated and characterized with NMR (1H, 13C, COSY, HSQC-DEPT, HMBC, 1D-TOCSY, and NOESY) and mass spectral data. Additionally, we emphasize the importance of 1D and 2D NMR techniques when identifying complex steviol glycosides. Numerous NMR spectroscopy studies of rebaudioside M (1), rebaudioside D (3), and mixture of 1 and 3 led to the discovery that SG17 which was previously reported in literature, is a mixture of rebaudioside D (3), rebaudioside M (1), and possibly other related steviol glycosides.

Abstract:To supply the increasing demand of natural high potency sweeteners to reduce the calories in food and beverages, we have looked to steviol glycosides. In this work we report the bioconversion of rebaudioside A to rebaudioside I using a glucosyltransferase enzyme. This bioconversion reaction adds one sugar unit with a 1→3 linkage. We utilized 1D and 2D NMR spectroscopy ( 1 H, 13 C, COSY, HSQC-DEPT, HMBC, 1D TOCSY and NOESY) and mass spectral data to fully characterize rebaudioside I.

Five new ent-atisene diterpene glycosides (1-5) have been isolated from Stevia rebaudiana Bertoni. This adds to a list of only 2 new ent-atisene diterpene glycosides isolated previously from S. rebaudiana. Diterpene glycosides isolated from S. rebaudiana, such as the rebaudiosides, are typically associated with the ent-kaurene core and glycosylation at the C-13 and C-19 positions. Extensive application of nuclear magnetic resonance spectroscopy techniques (1H, 13C, 1D-TOCSY, COSY, HSQC-DEPT, HMBC, and ROESY) as well as high-resolution mass spectrometry demonstrated that the ent-atisenes 1 to 5 had glycosylation patterns identical to rebaudiosides J, N, O, K, and T, respectively. We have named these compounds stevatisene J, N, O, K, and T, respectively.

In a continued search for novel diterpenoid glycosides, we recently isolated and characterized a Rebaudioside M derivative with a hydroxyl group at position 15 in the central diterpene core from an extract of Stevia rebaudiana Bertoni. Here we report the complete structure elucidation of 15α-hydroxy-Rebaudioside M (2) on the basis of NMR (1 H, 13 C, COSY, HSQC-DEPT, HMBC, 1D TOCSY, NOESY) and mass spectral data. Steviol glycoside with a hydroxyl group at C-15 in the central diterpene core has not been previously reported.

With our interest of new diterpene glycosides with better taste profile than Rebaudioside M, we isolated and characterized two steviol glycosides with three additional glucose attached at the C-13 of Rebaudioside M or Rebaudioside D from an extract of Stevia rebaudiana Bertoni. Here we report the complete structure elucidations of diterpene glycosides on the basis of NMR experiments (1H, 13C, COSY, HSQC-DEPT, HMBC, 1D TOCSY, NOESY) and mass spectral data. Steviol glycosides that possess eight or nine glucose units are rarely reported in literature and could have an impact on the natural sweetener catalog.