Phloroglucinol moieties

The glycosides of normal flavonoids (Table VII), except naringin, showed some precipitation alone, and without exception, precipitation increased considerably when they co-reacted with a few moles of phloroglucinol. The chalcones tended to precipitate more completely than the true flavonoids, probably because of the more free and reactive phloroglucinol moiety. 

Determine the conversion yield by summing the mass of the subunits (not including the phloroglucinol moiety) and dividing by the starting mass of proanthocyanidins ... 

The benzylic position in the phloroglucinol moiety of (+)penta-0-acetylcatechin in hot carbon tetrachloride reacted in preference to the ring in bromination during 5 hours with N-bromosuccinimide plus a small quantity of benzoyl peroxide with a 50% yield (83% conversion) and formation of the p-produrt (ref.22). 

Similar difficulties would be encountered using the acid sulfite process on other woods containing stilbenes or polyphenols such as proanthocyanidins containing resorcinol of phloroglucinol moieties. For example, dihydroquercetin has been identified as the cause of inhibition of calcium base sulfite pulping of Pseudo-tsuga menziesii (138). 

In the first of these, the key step in the synthetic sequence involves an oxidative phenol coupling reaction patterned after the biosynthesis of the natural product. Preparation of the moiety that is to become the aromatic ring starts by methyla-tion of phloroglucinol (5) with methanolic hydrogen chloride to give the dimethyl ether (6). Treatment of that intermediate with sulfuryl chloride introduces the chlorine atom needed in the final product (7). 

Consideration of the generalized aflatoxin structure represented in (I) leads one to the inescapable conclusion that at the core of the system is the A-ring in the form of a phloroglucinol nucleus, in which each of the pendant phenolic oxygen atoms is uniquely differentiated. Furthermore, two of the three carbon sites on this nucleus are differentially substitued with carbon moieties. This constitutes a potentially difficult synthetic circumstance in that not only must a high degree of substitution be provided for, but also a certain amount of regiochemical control must... 

Thus, in addition to the intact basic ring structure of the ABC system, one has attained both regioisomeric differentiation of the phenol necessary for the vonPech-mann condensation, and provision for the vinyl ether insertion in the form of the C-15 hydroxyl (or a possible derivative thereof). Indeed, it is evident that any of several directions may be taken in this route by variations in (a) the nature of the functional groups on the phloroglucinol nucleus and C-15 hydroxyl, (b) the timing of their introduction and removal and, (c) the timing for the introduction of the vinyl ether moiety. 

However, the structural combination of the phloroglucinol and terpenoid moieties appears to be a biosynthetic peculiarity of the Hypericum plants. 

Important antimicrobial activity is also described for phloroglucinol derivatives other than hyperforin. Thus, some of the phloroglucinols isolated from H. japonicum [55] have been assayed against Gram-positive bacteria and found to be particularly effective against S. aureus. The presence of a benzoyl group on the filicinic acid moiety, typical of their structure, seems to be essential for their bioactivity. 

Moreover, phloroglucinols from H. brasiliense, also containing a filicin acid moiety in their structure, have been found effective against B. subtilis [54]. 

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