Complete Structure Elucidation of New Steviol Glycosides Possessing 9 Glucose Units Isolated from Stevia rebaudiana

In our continued effort to discover new diterpene glycoside sweeteners from Stevia rebaudiana Bertoni with a better taste profile than that of rebaudioside M, we have isolated three novel steviol glycosides with 9 glucose units, 3 at the C-13 site of the aglycone backbone and 6 at the C-19 site. Compounds 2-4 contain an additional tri-glucosyl unit attached to the C-19 glycoside region of rebaudioside M. For compounds 2 and 3 this unit is attached via the relatively rare 1 -> 6 alpha-glycoside linkage. For compound 4 this additional unit is attached via the uncommon 1 -> 3 alpha-glycoside linkage. In this paper, we describe the complete structure elucidation of novel diterpene glycosides with 9 sugar moieties by NMR (H-1, C-13, COSY, HSQC-DEPT, HMBC, 1D TOCSY, NOESY) and mass spectral data.