Page 128 - Medicinal Plants_PharmD general

Test for Anthraquinone glycosides:
Modified Borntrager’s test:

1- If only glycosides are present, the test should be modified by first
hydrolysis with alcoholic potassium hydroxide solution then filter.

2- Acidify the filtrate with dilute hydrochloric acid and then filter (to
liberate the free aglycones).

3- Cool and shake with ether or benzene, (extract the free aglycones).
4- Separate the yellowish ethereal layer into a clean test-tube and shake

with dilute solution of ammonium hydroxide; an orange or deep
orange-red colour is produced in the aqueous layers.

Chromatographic identification of anthraquinone derivatives:
Silica gel is preferred for TLC of anthraquinone derivatives, many

solvent systems can be used for separating anthraquinone derivatives e.g.
ethyl acetate: methanol: water (100:16.5:13.5).
Visualisation: Anthraquinone derivatives may be detected on silica gel
layer through their fluorescence in UV light and also by spraying with
alkali solution where a more intense yellow, orange or red colour is
observed.

3. Flavonoid glycosides:

Definition:
- They are the largest group of naturally occurring phenols and occur in

the plant both in the free state and as glycosides.
- The flavonoid group may be described as a series of C6-C3-C6

compounds i.e. their carbon skeleton consists of two C6 groups
(substituted benzene rings) connected by a three carbon aliphatic chain.

C6 - C3- C6 skeleton

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