Proanthocyanidins reactions during

There are several caveats associated with this assay that may affect accuracy and precision. (+)-Catechin is the natural form in proanthocyanidins. Part of (+)-catechin epimerizes at the C2 position to form (+)-epicatechin during depolymerization. Similarly, part of (—)-epicatechin epimerizes to form (—)-catechin as an artifact. (+)-Catechin and (+)-epicatechin are an epimer pair in solution (similar to a- and 3-glucose in solution), i.e. they are chiral isomers that cannot be separated on a common reversed-phase HPLC column. The degree of epimerization increases with reaction temperature and time. Depolymerization at room temperature for 10 h caused less than 10% of flavan-3-ols to undergo epimerization. Toluene-a-thiol also causes the heterocyclic ring fission of flavan-3-ols to form adducts that... 

The elegance of this simple biomimetic approach to the synthesis of proanthocyanidin oligomers was demonstrated during synthesis of the mixed profisetinidin trimers (22) and (23), i.e. analogues possessing different ABC and GHI chain extender units. Triflavanoid (22) with its fisetinidol ABC and epifisetinidol GHI units was formed by acid-catalyzed reaction of fisetinidol-(4a->8)-catechin (24) (57) and epifise-... 

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