Chemical Study on Structure and Activity of Cucurbitane type Triterpene Glycosides.

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Isolation and structure elucidation of cucurbitane glycosides from Chinese cucubitaceous plants, were conducted.From tubers of Hemsleya carnosiflora. eight new glycoside named carnosifloside I-VI(C-I-CI) were isolated and their structures were established. From tubers of H.panacis-scandens, seven new glycosides named scandenoside R1-7(S-R1-7) were isolated together with C-1-III, V and VI. Structures of S-R1-7 were elucidated.From fruits of Siraitia siamensis, mogrosides-IV and V sweet principles of Siraitia grosvenorii (=Mordica grosvenori) together with two new glycosides, the structures of which were assigned as 11-keto-mogroside-V and 3-0-B-glucosyl-26-0-[B-glucosyl-(1 2)]-[B-glucosyl-(1 6)]-B-glucosyl-mogro, respectively.For these natural glycosides as well as compounds derived from the natural glycosides by chemical or enzymic procedures, the relationship between taste and structure was investigated. (1) Compounds with only one or two glucosyl units such as C-i, S-R1-4, are tasteless. (2) 11 -0H glycosides with more than three glucosyl units such as mogroside-V,C-V, -VI and S-R6, are sweet. (3) 11B-0H glycoside a such as S-R7 are tasteless even if they have more than three glucosyl units. (4) 11-keto glycoside a taste bitter. However, the increase of glucosyl unit results in change of taste from bitter to sweet. For example, 11-keto-mogroside V is a glucopentoside, exhibiting sweetss. The bitterness of an 11-keto glucotrioside, C-III is decreased by enzymic glucosylation at the 26-gentiobiosyl moiety with starch and cyclodextrin-glucosyl transferase.