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Steviol glycosides obtained from Stevia rebaudianaleaves are increasingly used in the food industry as natural low-calorie sweeteners. Among them, the sweetness of major glycosides composed of glucose residues (e.g., stevioside and rebaudioside A) has been widely studied. However, the properties of minor natural products containing rhamnose or xylose residues are poorly investigated. In this study, five unreported steviol glycosides containing rhamnose or xylose were extracted from our developing stevia leaves, and their sweetness was evaluated. The highly glycosylated steviol glycosides were identified, and their structures were examined by fragmentation analysis using mass spectrometry. Chemical synthesis of these glycosides confirmed their structures and allowed sensory evaluation of minor steviol glycosides. Our study revealed that a xylose-containing glycoside, rebaudioside FX1, exhibits a well-balanced sweetness, and thus, it is a promising candidate for natural sweeteners used in the food industry.

Dibenzyloxycarbonyl- and di-t-butyloxycarbonyl-l-β-lysine were synthesized from corresponding diacyl-l-ornithine by modified Arndt-Eistert reaction involving diazoketone preparation viathe mixed carbonic carboxylic anhydride. These diacyl-β-lysine derivatives are required for total- or semi-syntheses of peptide antibiotics, tuberactinomycins or streptothricins.