The First Total Synthesis of Rebaudioside R

With easily available monosaccharides and steviol as starting materials, the first total synthesis of rebaudioside R with a xylosyl core in the C13–OH linked sugar chain was accomplished via two distinct approaches. The first approach features the stepwise installation of branch-sugar residues via an order of C2–OH first and then C3–OH of the xylosyl core, laying a firm foundation for the synthesis of analogues with different branch sugars, while the second route features the introduction of the C13 trisaccharide sugar chain via a convergent strategy, securing the overall synthetic efficiency. Through the synthetic study, the effect of protecting groups (PGs) at the vicinal hydroxy group on the reactivity of OH acceptors was illustrated.