Monomeric ellagitannins

PADPRH (tetrameric> trimeric > dimeric > monomeric ellagitannins gallotannins i.e. more complex more potent)... 

Fig. 64,17 Punicalagin, a glucopyranosic monomeric ellagitannins found in Punica granatum...

This classification still left out many monomeric ellagitannins the structures of many of which result from chemical transformations other than those strictly mediated by oxidative processes. In this vein, some important structural modifications have to do with the opening of the o-glucopyranose core, the formation of C-aryl glucosidic bonds, and condensation reactions taking place at the glucose C-1 locus. As these ellagitannins still... 

The DOG type units are also subdivided into their meta and para variants. In these units, a HHDP unit is 0-C-linked to a G unit. The m-DOG type unit that is also referred to as the valoneoyl unit is found in numerous oligomeric ellagitannins (Okuda et al, 1993), as well as in some monomeric ellagitannins such as the aforementioned type III+ mallotusinic acid (15, Fig. 4.4). The dimer oenothein B (20, Hatano et al, 1990a), isolated in... 

Fig. 4.9 Punicalagin, an example of glucopyranosic monomeric ellagitannins featuring a tetiaphenyi ellagic acid-containing gallagyl unit.

Li, H. Tanaka, T. Zhang, Y.J. Yang, C.R. Kouno, I. 2007. Rubusuaviins A-F, Monomeric and oligomeric ellagitannins from Chinese sweet tea and their alpha-amylase inhihitory activity. Chem. Pharm. Bull. 55 1325-1331. 

The ellagitannin composition of extracts from the duramen depends on the species of oak. All four monomeric and four dimeric (roburin A, B, C, and D) ellagitannins are present in the three species of European oak, while the American species have practically no dimers. 

Fig. 64.12 Putative pathway from monomeric C-glycosidic ellagitaimins to oligomeric and glycosilated C-glycosidic ellagitannins as well as to llavano-ellagitannins. Acid-catalyzed condensation reactions of C-glycosidic ellagitannins via benzylic-type carbocation intermediates...

No evidence has yet been obtained to show that dimeric products are formed by oxidative coupling of the monomeric species such as was noted in Class 2B (vide supra). However, brief comment should be made on two phenolic metabolites, isolated early in the studies of the ellagitannins chebulinic acid (91,140) and chebulagic acid (91) (Table 7.2.9). It is clear from biogenetic considerations that these are phenolic metabolites very probably derived by further oxidative ring fission of one aryl ring in a precursor such as geraniin (51). 

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