The analytical values of the glycoside A agree with that of a mixture of kaempferol monorhamnoside and 3, 5, 7, 4′-tetrahydroxyflavanone monorhamnoside but the separation of these two substances by various solvents proved difficult. Methylation of glycoside A with diazomethane under mild conditions and hydrolysis of the product afforded 3, 5-dihydroxy-7, 4′-dimethoxyflavone (III) as yellow needles, m.p. 179-180° and 3, 5-dihydroxy-7, 4′-dimethoxyflavanone (IV) as colorless needles, m.p. 189-190°. when a large excess of diazomethane was applied, hydrolysis of the product afforded 3-hydroxy-5, 7, 4′-trimethoxyflavone (V) as pale yellow needles, m.p. 145-146°, and 3-hydroxy-5, 7, 4′-trimethoxyflavanone (VI) as amorphous substance of m.p. 60° (indistinct). Therefore, the glycoside A is assumed to be a mixed cystals of kaempferol 3-L-rhamnoside (VII) and 3, 5, 7, 4′-tetrahydroxyflavanone 3-L-rhamnoside (VIII). (VIII) can be isolated by adsorption of (VII) on carbon from 70% ethanolic solution of the glycoside A.
The hydrolysis of glycoside B (IX), C
21H
22O
10, afforded L-rhamnose and
rac.-3, 5, 7, 4′-terahydroxyflavanone, m.p. 231-232°. Application of an excess of diazomethane followed by hydrolysis results in the formation of 3-hydroxy-5, 7, 4′-trimethoxyflavanone as an amorphous substance of m.p. 60° (indistinct). Therefore, (IX), as (VIII), is assumed to be 3, 5, 7, 4′-tetrahydroxyflavanone 3-L-rhamnoside.
Both (VIII) and (IX) give reactions common to flavonoids and their ultraviolet absorption spectra suggest them to be flavanonol compounds (Fig. 1) They are probably stereoisomers. Both are new substances and were named engelitin (VIII) and isoengelitin (IX).
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