Prenylated phenolic compounds

One reason that dominant plants are successful in semi-arid and arid ecosystems is due to the high concentration of terpenoids and prenylated phenolics that repel and/or deter feeding by herbivorous insects. Compounds like sesquiterpene lactones and benzopyrans are present in high quantities in the leaves of species of Pjajl t h ij jn, E n c e l i a and D i c o r i a and have been demonstrated to be effective feeding deterrents against known economic insect pests. Ijt vivo experiments are still needed in the field with bioactive constituents to better understand their effects on native phytophagous insects. 

Other antimicrobial phenolic compounds from the Anthemideae tribe are coumarins, which are derivatives of benzo-a-pyrone. Feresin et al. [199] isolated eight / -coumaric acid derivatives from the Argentinian medicinal plant Baccharis grisebachii. Two of them, 3-prenyl-/ -coumaric acid, Fig. (38) and 3,5-diprenyl-p-coumaric acid were active towards Epidermophyton floccosum and Trichophyton rubrum, with MIC values of 50 and 100-125 ig/ml, respectively. 

It is also noteworthy that some of the phloroglucinols isolated from Hypericum species, are characterized by O-prenylation, which, in contrast to C-prenylation, is quite rare for natural phenolic compounds. 

Synthesis of Prenyl Oxygen Ring Phenolic Compounds... 

Triterpenoid Saponins Phenolic Compounds Recent Methods of Structure Determination of Prenylated Phenols Biological Activities of Phenolic Constituents of Glycyrrhiza Species... 

In our study of the species, the main phenolic compounds with prenyl group(s) were licoricidin (164,0.011%), licorisoflavan A (165,0.0025%) and glycyrol (169, 0.0023%). We also isolated twelve new isoprenoid-substituted phenols as minor constituents, kanzonols F-Q (178-189), from the underground parts (261, 284, 285). Kanzonols M (185), N (186), and O (187) are rare isoflavans with a formyl group on the A ring. The structures of the diprenylated isoflavones, kanzonols K (183) and L... 

There are a number of reports dealing with the phenolic constituents of the aerial parts of Glycyrrhiza species. About thirty new prenylated phenols have been isolated these compounds are not generally found in the underground parts. 

Forty phenolic compounds have been isolated from the aerial parts. We isolated twenty-one phenolic compounds from the aerial parts collected in Heilogjang Province in northeastern China 346-348). Among these, gancaonin A (274) was isolated for the first time as a natural product and fifteen compounds, gancaonins B-E and L-V (275-289) were isolated as new compounds. Among these, gancaonins A (274), B (275), L (279), M (280) and N (281) are prenylated isoflavones. 

Table 3. The Chemical Shifts of Methylene Carbons of Prenyl (Geranyl) Groups of Phenolic Compounds (6 in ppm)...

Table 13. Structures and Plant Sources of Phenolic Compounds (the structure shows in parenthesis as follows isoflavone (3, 5,7-3 x OH, 6-prenyl, Dmp[5, 4 ]) means 2",2"-dimethylpyrano[5",6" 5, 4 ]-6-prenyl-3, 5,7-trihydroxyisoflavone (260) HPLC = detection with HPLC analysis ud = our unpublished data n.r. = not reported callus means cell cultured of Glycyrrhiza species)...

The synthesis of 4 involves ten initial steps to achieve alcohol 54 from tyrosine (16% overall yield) and pursues with the change of the alkyl side chain on the phenolic hydroxyl group (Scheme 46). Thus, O-demethylation of 54 followed by prenylation and treatment of the resulting lactam with LiAlH4 gaves azaspiranic compound 149. Protection of the secondary amine and oxidation of both alcohols using TPAP/NMO lead to the keto aldehyde 150. Treatment of the latter with Cd/Pb couple [78] allows the deprotection of the secondary amine as well as the cyclization process to provide (+)-TAN1251C (4). 

Probably because prenyl derivatives of dihydric phenols are more involved naturally and more reactive than those of the monhydric series as the precursors of many cyclic oxygen ring compounds they have attracted synthetic interest. Although the alkylation of hydroquinones affords good yields, the more reactive resorcinol series do not respond well and isomer formation occurs. Thus, (ref.9), hydroquinone as the disodium salt in hot benzene with 3-methylbuten-2-yl chloride gave 4-hydroxy-2-(3-methylbuten-2-yl)phenol in 66%... 

As with prenylphenols in the monohydric series mild acid-catalysed procedures have been developed for the prenylation of polyhydric phenols. Thus a variety of these compounds have been condensed with 3-methylbut-2-enol and with 2-methylbut-3-en-2-ol in dilute aqueous formic acid. Hydroquinone for example afforded isopentenylhydroquinone, 4-hydroxy-2-(3-methylbuten-2-yl)phenol (ref. 15). 

Although many of the complex natural chromene, chroman, pyran and benzofuran structures clearly have arisen from reactive prenyl precursors which themselves have invariably not been isolated, certain prenyl derivatives of dihydric phenols have served as model compounds in cyclisation processes likely to be the pathways towards those naturally occurring compounds. 2-Prenylphenols and 2- and 4-prenylresorcinols and orcinols with C5, C o, and... 

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