Proanthocyanidins (19) can be classified according to variation in hydroxylation
pattern into several subgroups like propelargonidins (3,4ʹ,5,7–OH) (20), procyanidins
(3,3ʹ,4ʹ,5,7–OH) (21), prodelphinidins (3,3ʹ,4ʹ,5,5ʹ,7-OH) (22), proguibourtinidins
(3,4ʹ,7-OH) (23), profisetinidins (3,3ʹ,4ʹ,7-OH) (24), prorobinetinidins
(3,3ʹ,4ʹ,5ʹ,7-OH) (25), proteracacidins (4ʹ,7,8-OH) (26), promelacacidins
(3ʹ,4ʹ,7,8-OH) (27), pro-apigeninidins (4ʹ,5,7-OH), and proluteolinidins
(3ʹ,4ʹ5,7-OH) (Fig. 21.3) (Khanbabaee and Van Ree 2001).
21.3.4 Complex Tannins
Complex tannins are formed when, a hydrolysable unit binds with a gallotannins or
an ellagitannins through a glycoside linkage. An example of complex tannin is
acutissimin A (27), which is isolated from the bark Korean chestnut (Castanea
OH
OH
OH
O
O
O
HO
O
O
O
O
OH
OH
HO
O
OH
OH
OH
HO
OH
HO
OH
HO
OH
O
O
O
O
O
O
O
O
O
OH
OH
HO
OH
OH
HO
OH
HO
OH
HO
HO
HO
O
OH
HO
HO
O
HO
HO
O
OH
HO
HO
OH
O
HO
OH
HO
4
1
2
3
O
O
O
O
O
O
O
OH
OH
O
O
O
OH
OH
O
O
OH
OH
HO
OH
HO
HO
O
OH
HO
O
O
OH
OH
OH
O
HO
HO
O
O
OH
HO
HO
O
HO
OH
O
O
HO
HO
HO
5
O
OH
O
O
O
O
OH
OH
OH
HO
OH
HO
OH
O
O
O
O
O
O
O
O
O
OH
OH
HO
OH
OH
HO
OH
O
OH
HO
HO
HO
O
OH
HO
O
O
HO
OH
HO
O
OH
HO
HO
O
OH
O
O
O
O
OH
OH
HO
HO
OH
HO
OH
OH
8
7
6
Fig. 21.1 Structures of some gallotannins
21 Tannins and Polyphenols Extracted from Natural Plants …
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