intermediates and ellagitannins are formed due to the oxidation leading to C–C
linkage.
21.4.1 Biosynthesis of Hydrolysable Tannins
Hydrolysable tannins biosynthesis starts from gallic acid synthesis from quinic acid.
Quinic acid comes from the one of the most important intermediate in glycolysis in
plant, phosphoenolpyruvate. Phosphoenolpyruvate via phosphoenolpyruvate
O
OH
HO
OH
OH
O
O
HO
HO
OH
OH
OH
OH
O
16
O
HO
OH
OH
OH
OH
17
O
OH
OH
18
19
O
OH
HO
OH
OH
O
O
HO
OH
HO
HO
OH
20
O
HO
OH
OH
OH
OH
21
O
HO
OH
OH
OH
OH
O
HO
OH
OH
OH
OH
OH
OH
22
(Prodelphinidin B 1 )
O
HO
OH
OH
O
HO
OH
OH
23
O
HO
OH
OH
OH
24
O
HO
OH
OH
OH
OH
25
O
HO
OH
OH
26
Fig. 21.3 Structures and basic units of condensed tannins
OH
HO
HO
HO
HO
HO
HO
HO
O
O
HO
O
O
O
O
O
O
O
O
OH
OH
OH
OH
OH
HO
O
HO
HO
HO
OH
OH
27
O
O
HO
OH
OH
OH
OH
O
OH
OH
OH
28
OH
O
O
OH
HO
HO
OH
HO
HO
O
O
HO
HO
OH HO
OH
OH
O
O
O
O
OH
HO
OH
HO
OH
29
Fig. 21.4 Structures of some complex tannins
21 Tannins and Polyphenols Extracted from Natural Plants …
727