Hydrolysable tannins activity

On the basis of the studies concerning the activity of the hydrolysable tannins from Phyllanthus amarus (Euphorbiaceae), it seems that their effectiveness against common protein kinases is lower than that of condensed tannins. In fact, IC50 values ranged from 0.2 to 1.7 pM for the rat liver PKA-catalytic subunit, and was 26 pM for geraniin (11) and other closely-related compounds against rat brain PKC. Other tannins of the same plant inhibited PKC at the high fixed dose of 167 pM [38]. 

This information, in concert with the fact that no aflatoxin-suppressing activity is extractable with hexane, but with the demonstrated occurrence of activity in all other solvent extracts and even in exhaustively extracted residue, is consistent with activity being associated with the hydrolysable tannin content or composition of the pellicle. 

Black walnut cultivars Rawlins and Thomas had considerably lower gallic acid levels of -1% dw, quite close to that of the pistachio cultivar Kerman (0.5% dw), and in vitro aflatoxin production for the walnut Thomas and pistachio Kerman were also similar at 45 and 40 J,g/plate, respectively [17], The hydrolysable tannin in pistachios has a core of quinic acid, rather than glucose (unpublished results), and its stereochemistry is such that dimerization of gallic acid moieties to hexahy-droxydiphenic esters, and consequent formation of ellagic acid, cannot occur. Any aflatoxin inhibitory activity is, therefore, dependent on either the tannin itself or gallic acid. 

Yoshida T, Chou T, Matsuda M, Yasuhara T, Yazaki K, Hatano T, Nitta A, Okuda T (1991) Woodfordin D and oenothein A, trimeric hydrolysable tannins of macro-ring structure with antitumor activity. Chem Pharm Bull 39 1157-1162... 

Yoshida, T, Chou, T., Nitta, A., Miyamoto, K., Koshiura, R. Okuda, T. (1990a). Woodfordin C, a macro-ring hydrolysable tannin dimer with antitumor activity and accompanying dimers from Woodfordia frutocosa flowers. Chemical and Pharmaceutical Bulletin, 38, 1211-1217. 

The dimeric hydrolysable tannin isolated from Cornus ojficinalis fruits, comusiin A, showed a potent inhibitoiy effect on reverse transcriptase of avian myeloblastosis virus [Kakiuchi et al., 1985] and also antisarcoma activity [Myamoto et al., 1987], Comusiin B presented a high a-glucosidase inhibitory effect [Omar et al., 2012],... 

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