Efficient preparation of catechin thio conjugates by one step extraction/depolymerization of pine (Pinus pinaster) bark procyanidins

The skin penetrating antioxidant cysteamine derivative of (-)-epicatechin as well as other thio conjugates were efficiently obtained with high yields from pine (Pinus pinaster) bark by simultaneous one pot extraction and depolymerization using water and cysteamine hydrochloride. The influence of the concentration of bark, acid, and cysteamine, as well as the reaction time on the total conversion, was studied. The total conversion into the epicatechin and catechin conjugates was as high as 47 g/kg pine bark with 1666 g cysteamine/kg bark and 28 g/kg with 166 g cysteamine/kg bark. A fast cleanup step by absorption/desorption on XAD-16 greatly facilitated further purification of the active major component. At a pilot scale, 4beta-(2-aminoethylthio)epicatechin (1) (conversion 263 g, purity 35% by reversed phase high-performance liquid chromatography/weight) was obtained from 17 kg of pine bark after simultaneous extraction/depolymerization followed by cleanup with the polymeric resin in approximately 10 h. The results show that pine (P. pinaster) bark is a suitable source of flavanols for the preparation of active thio derivatives. Conditions are given for the fast and efficient preparation of the conjugates.