New lipophilic catechin derivatives by oxa-Pictet-Spengler reaction

Synthesis of lipophilic catechin derivatives was carried out to improve their solubility in lipidic substances that must be protected against oxidation. For this purpose, an oxa-Pictet-Spengler coupling reaction, which is not only conservative for antioxidative activity, but also simple, mild and inexpensive, was applied. This method permitted grafting of alkyl chains, from various methyl ketones, between the C and B rings of catechin. The derivatives were isolated, on the one hand, by silica gel column chromatography and, on the other, by simple aqueous washing of the crude product. Both treatments produced almost the same purity; products of the second one had best antioxidative activities given by inhibition of the induced oxidation of methyl linoleate and by reactivity with the free radical 2,2-diphenyl-picrylhydrazyl. All derivatives acquired a lipophilic character as proven by measurement of the partition coefficient between octanol and water.