Catechin washing

Catechin (226.7 mmol) was dissolved in 720 ml DMF and NaH (975 mmol) in 180 ml DMF added. After stirring at ambient temperature 50 minutes, the flask was cooled to -10 °C and benzyl bromide (1.02 mol) added dropwise over 80 minutes. The reaction mixture was warmed to ambient temperature overnight and the solution concentrated. The residue was dissolved in CH2CI2, washed with water, and extracted with chloroform. It was purified by chromatography using silica gel with acetone/chloroform/hexane, 1 12 7, the crude product re-crystallized in trichloroethene, and the product isolated 24% yield. H-NMR, IR, and MS data supplied. 

Gravimetric Method 25 ml of extract were acidified with HCl to pH=l and a molar excess of formaldehyde was added. This excess was calculated assuming that catechin and formaldehyde react in a 1 1 proportion. The suspension was refluxed during 30 min. The reaction products were filtrated, washed several times with hot water and dried to constant weight at 100 X. The polyphenol content is expressed in absolute terms by the Stiasny precipitation number with formaldehyde , %, defined by ... 

Brugirard and Tavernier (1952) used the property of true tannins of flocculating a solution of 1% gelatine in 10% sodium chloride for their tannin determination in cider. They determined the total tannoids (T) by the Neubauer-Loewenthal procedure, then precipitated the true tannin in a buffered solution with 2.0% cinchonine sulfate, and determined the non-tannin polyphenols (< ) in the centrifugate. T — V thus equals the true tannins. Since the tannin content decreases with time, Fessler (1947) noted that the age of the sample should be stated along with the tannin results. Rentschler and Hauser (1950) precipitated the catechin tannins in a hot acid solution with formaldehyde, filtered, washed with alcohol and ether, dried and weighed. The anthocyanin pigments were reported not to interfere. 

The approach we have found to be most useful for the isolation and purification of Type 1 or 2 proanthocyanidin polymers is extraction from plant tissue with acetone-water mixtures (25, 37), separation of the monomers and lower oligomers from the resulting aqueous solution with ethyl acetate, adsorption on Sephadex LH-20 of the aqueous solution diluted with an equal volume of methanol and washing with the same solvent to eliminate impurities. The polymer is then displaced with acetone-water to yield freeze-dried analytically pure material (25). In the case of procyanidins, the ethyl acetate fraction contains monomers (catechin or epicatechin), dimers, trimers, and some tetramers, whereas the LH-20 fractions contain tetramers, on up to genuinely polymeric species. 

---