From leaves of Stevia rebaudiana, the major sweet principle, stevioside(S) has been isolated together with rebaudioside A (RA) and several other minor sweet glycosides (Table 1). From leaves of Rubus suavissimus, the homologuous sweet glycoside, rubusoside (RU) has been isolated(Table 1). A number of more glucosylated compounds were prepared from S, Ru and their derivatives by trans-1,4-α-glucosylation with starch and cyclodextrin-glucosyltransferase (CGTase) (Tables 2,3 and Fig. 1). Evaluation of sweetness of these products revealed that elongation of 13-O-glycosyl moiety (total: 3 or 4 glucosyl units at 13-OH) resulted in remarkable improvement of the sweetness, while compounds with more glucosyl units in this moiety (total: 5 or 6 glucosyl units) exhibited rather worse sweetness. An increase in glucosyl units at the 19-position led to a change in the sweetness for the worse. Selective synthesis of the good sweeteners found in the above study was schieved by using a galactosyl group as a blocker against the transglucosylation with starch and CGTase (Figs. 2, 3).
