Pentahydroxyflavan

Assembly of fragments A-C, taking into aecount the ninth double-bond equivalent, leads to the 3,5,7,3, 4 -pentahydroxyflavane skeleton D and to the following assignment of H chemieal shifts ... 

Figure 11.4.1 Generalized proanthocyanidin structure indicating subunit type (extension or terminal) and interflavonoid bond location (4p- 8). The most common proanthocyanidin classes in the plant kingdom, as well as in the food and beverage industry, are the procyanidins (3,3, 4, 5,7-pentahydroxyflavans) and prodelphinidins (3,3, 4, 5, 5,7-hexahydroxyflavans). In addition, these proanthocyanidins can be galloylated at C3.

Samaraweera U, Sotheeswaran S, Sultanbawa M U S 1983 3,4,7,3, 5 -Pentahydroxyflavan and 3-methoxyfriedelan from Humboldtia laurifolia. Phytochemistry 22 565-567... 

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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