Chapter 10 - Studies on Prodelphinidins: Isolation, Synthesis, and Their Biological Activities

Abstract

Proanthocyanidins are known as condensed or nonhydrolyzable tannins whose structures are consisted of flavan-3-ols. These compounds are widely distributed in the nature such as vegetables, fruits, and plants. Proanthocyanidins have been reported to exhibit strong free-radical scavenging and antioxidative activities. Many significant biological activities such as antitumor, antiviral, and antiinflammatory were reported. Thus proanthocyanidins are increasingly recognized as possessing health beneficial effects for humans. The various types of proanthocyanidins exist in the nature. Among the proanthocyanidins, the reports of the studies on prodelphinidins which possess (-)-gallocatechin and/or (+)-epigallocatechin units are quite limited probably due to the difficulty to obtain pure materials from the nature. The structural diversity of these compounds exhibits various types of the configurational differences such as C3 and C4 chiral centers and the regioisomers and stereochemistries of the interflavan bonds (C4 to C8). Because their identification as well as purification is extremely difficult even using modern methods of isolation techniques, further investigation of the biological activities, ie, mechanism of action of the bioactivities, remains unknown. Quite recently, in order to obtain pure prodelphinidins, Makabe and coworkers reported the first synthesis of prodelphinidin B1–B4, and C2 and their antitumor activity [1], [2]. Here the author wishes to introduce isolation, the recent synthetic approaches toward prodelphinidins, and their biological activities.