There are two major classes of
condensed tannins (or as they are known more properly, polyphenolics)
naturally occuring in grapes. The only difference between the
two classes is the presence of one additional hydroxyl group on the B ring of
the three ring structure for prodelphinidin. The names for the
two classes are derived from the following: when a polymer of procyanidin is
hydrolyzed in strong acid, it will yield anthocyanidin cyanidin;
prodelphinidin will yield delphinidin.
This strucure represents a longer procyanidin
structure with the lower terminal unit and subsequent extension units of either
catechin or epicatechin. A gallic acid may be esterified to the
3 position, which would increase the hydrophobicity at the center of the
oligomer or polymer.
Structure of the main procyanidin dimers from V.
The upper two structures
illustrate examples of dimers of eppicatechin and catechin, each bonded between
the 4 position of the upper molecule and the 8 position of the lower molecule.
The configuration cis or trans of the bond between the C and B rings with the
hydroxyl located on the 3 position of the C ring determines whether or not the
structure is epicatcechin (cis) or catechin (trans). The lower
set of structures shows bonding between the 4 and 6 positions which would cause
branching of longer oligomers of polymers.