Plant cells are superior chemists and humans will never catch up with these skills: the fanciest tannins must be purified from plant sources now and in the future?
It is quite difficult to study the true bioactivities of polyphenols without both full purification and full identification of the studied molecules. We can achieve both of these goals and the purification can be extended to even gram quantities, if needed. In these cases all the polyphenols are isolated from plant sources, since we currently do not synthesize any other polyphenol in addition to pentagalloyl glucose (production from tannic acid).
Only a very limited number of monomeric ellagitannins can be produced via synthesis and with oligomers the situation is even worse. Therefore it is important to be able to produce these compounds by the help of chemical machineries of plants. Our expertise in purification remains especially with complex polyphenols such as ellagitannins. At the moment these can be purified from monomers up to heptamers range. Naturally the more simple polyphenols like flavonoid glycosides can be purified with less the effort.
Typically all the polyphenol purification steps include large-scale extraction, extract purification, gel chromatography and preparative or semi-preparative LC.