medicinal interest, for this reason, the structures of ellagitannins have been elucidated by analytical techniques (Fig. 10.17). The elucidated structures comprise
geraniin sequestered from Geranium robertianum known as Herb Robert and also
Geranium maculatum called as American cranesbill (Catarino et al. 2017) and
tellimagrandins 1 and 2 sequestered from Quercus alba called as Oak bark, Punica
granatum known as pomegranate and Filipendula ulmaria called as Meadowsweet
(Yi et al. 2004).
Condensed tannins, or proanthocyanidins, or non-hydrolyzable tannins are very
much reverberating to hydrolysis. These substances are oligomeric flavonoids
derived from flavones like flavan-3-ol, flavan 3,4-diol, or catechin. The characteristics of such types of tannins depend upon four parameters namely, the type of
linkages between flavonoid units; hydroxyl group arrangement, or the enantiomeric
COOH
OH
OH
O
H
Gallic acid
O
H
O
H
O
H
OH
OH
CO- O-Glu
OH
OH
OH
Pyrogallal
Catechol
Glucogallin
CO
O
O CO
OH
O
H
OH
OH
Ellagic acid
O
H
OH
OH
COOH
COOH
O
COOH
O
Chebulic acid
Catechin (Condensed tannin)
O
O
H
OH
OH
OH
OH
Fig. 10.17 The structure of some hydrolyzable tannins
350
C. C. Kandar