Penta-0-galloyl

Finally brief comment should perhaps be made on the overall pattern of metabolites which derive in a large number of plants from the pivotal intermediate B-penta-0 -galloyl-g-glucose (40). The pathways leading to a great many of the biosynthetic end-products are clearly catabolic in character (Fig. 19) - dehydrogenation is the common means of chemical transformation of 40. 

Fig. 7.2.4. Conversion of )5-penta-0-galloyl-D-glucose (15) to gallo- and ellagitannins...

Tb date, the ester 17a,b is the most widely encountered in the plant kingdom and it is worth noting that in plants that metabolize this phenol it overwhelmingly dominates the phenolic extract. The ester 17a,b has Rp values very similar to those of )ff-penta-0-galloyl-D-glucose (15) and is distinguished by preparative chromatography on Sephadex LH-20. Thble 7.2.4 shows plants in which this complex phenol has been identified. 

From the leaves of Comus officinalis a novel gallotannin, 1,7-di-O-galloyl-D-sedoheptulose, has been isolated. 1,2,3,4,6-Penta- and 1,2,3,4-tetra-O-galloyl- -D-glucose have been shown to be inhibitors of human placenta aldose reductase and of a mitochondrial oxidoreductase, respectively, and the ability of penta-0-galloyl-/J-D-glucose and twenty-four related, more complex, natural, hydrolysable tannins to scavenge radicals (e.g.. superoxide radicals) has been demonstrated. ... 

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