Polyphenols Oligomeric proanthocyanidins

Recent scientific investigations of natural polyphenols have demonstrated their powerful antioxidant property (Niki et al, 1995). Several classes of polyphenols have been chemically identified. Some of these are grape polyphenols, tea polyphenols, soy polyphenols, oligomeric proanthocyanidines (OPA) and other natural polyphenols of the flavone class. Rice bran polyphenols are different from the above in that they are p-hydroxy cinnamic acid derivatives such as p-coumaric acid, ferulic acid and p-sinapic acid. Tricin, a flavone derivative, has also been isolated from rice bran. 

Proanthocyanidins is a class of flavonoids. Proanthocyanidins are derived from the flavonoids oligomeric proanthocyanidins (OPCs) and therefore proanthocyanidins have been formerly called condensed tannins. Moreover, all proanthocyanidins have similar structures and the only differences are slight changes in the shape and attachments of the polyphenol rings. The diverse proanthocyanidins could always be found together, ranging from a proanthocyanidin unit to complex molecules with many linked units as the oligomers in nature. 

Phytochemical Content high in carotenoids (beta-carotene), polyphenols (anthocyanins, oligomeric proanthocyanidins, tannins, luteolin, quercetin, apigenin)... 

Roles of Polyphenols, Flavonoids, and Oligomeric Proanthocyanidins in Cancer Chemoprevention... 

The polyphenols are a series of phytochemicals synthesized by plants. They include the bioflavonoids anthocyanins, coumestanes, flavonoids, isoflavonoids, and stil-benes (Figure 4.1). Each bioflavanoid class is subdivided into other groups, e.g., flavones, flavans, flavanols, flavonols, and flavanones (Figure 4.2). Another class of polyphenol is the oligomeric polyphenols, such as the proanthocyanidins, found in the grape and various berries (black currant, blueberry, etc.). 

The in vivo assay for evaluation of antitumor activity of other tannins and related polyphenols was thus routinely performed by administration of tannins with a single intraperitoneal injection (10 mg/kg) to female ddY mice 4 days before inoculation of sarcoma 180 cells (1 x 10 ). Sixty days after inoculation of the tumor cells, survivors were killed and autopsied. The antitumor activity of each tannin was estimated by the number of regressors and the % increases in the life span (% ILS) [107]. Among approximately 100 polyphenols of different types tested, most of the oligomeric hydrolyzable tannins exhibited a potent activity in contrast to the negligible activity of the monomeric hydrolyzable tannins, proanthocyanidins and their related low-molecular weight polyphenols such as gallic acid, catechins and caffeoyl derivatives. 

More recently, Roux and co-workers (149) have isolated a complex array of oligomeric polyphenols based on (2jR,3S)-3,3, 4, 7,8-pentahydroxyflavan from the heartwood of mesquite (Prosopis glandulosa). These include some oligomers linked by normal proanthocyanidin interflavanoid linkages (i.e. 4- 6), but predominantly the form of linkage has arisen from oxidative coupling to form biphenyl and m-terphenyl interflavanoid bonds. These are just the sort of bonds expected to be formed in secondary processes in any proanthocyanidin polymer, and it is still an open question as to the extent of these processes in outer bark and heartwood. 

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