8-Prenylated flavanones

Three prenylated flavanones (144-146) isolated from stem barks of Erythrina abyssinica (family Liguminosae) exhibited inhibitory activity against protein tyrosine phosphatase IB (PTPIB) in an dose-dependent manner with IC50 values of > 60, 18.9 1.9 and 15.7 0.4 /tM, respectively hence, the flavanone (143) bearing a 2,2-dimethylpyran moiety on B ring is less potent than the other two (144 and 145) in the series. The... 

Garo, E. et al., Prenylated flavanones from Monotes engleri. Online structure elucidation by LC/ UV/NMR, Helv. Chim. Acta, 81, 754, 1998. 

The formation of phytoalexins such as glyceollins and phaseollins requires C-prenylation by a range of pterocarpan prenyltransferase (PTP) activities, with dimethylallyl pyrophosphate (DMAPP) as the prenyl donor. For glyceollins and phaseollins, prenylation occurs at position C-2 or C-4 of glycinol or C-10 of 3,9-dihydroxypterocarpan. ° ° However, there are differing activities in other species. For example, in Lupinus albus (white lupin) a prenyltransferase acting at the C-6, -8, and -3 positions of isoflavones has been identified.PTPs have also been characterized in detail for the formation of prenylated flavanones in Sophora flavescens (see, e.g., Ref. 207). However, no cDNA clones for flavonoid-related prenyltransferases have been published to date. 

From a chemosystematic point of view, it is interesting to note that prenylated flavonoids such as microfolione (56) have been found in a species of the family Ptaeroxylaceae, because the relationships of this family with other families were disputed in the past. Most taxonomists considered the Ptaeroxylaceae closely related to families in the order Rutales to which the Rutaceae and Meliaceae belong, whereas others considered it related to the Sapindaceae. Flavonoid chemistry supports a close relationship to the Rutaceae and Meliaceae, as iso-prenylated flavanones also occur in these families, e.g., 58 and 98 in Boronia coerulescens ssp. spinescens, the farnesyl-bearing 121 (Figure 15.3) in B. ramosa (Rutaceae)," and flowerine (59) and flowerone (60) in Azadirachta indica (Meliaceae). Microfolione is one of the few new flavanones for which the (2i )-configuration has been determined. 

Aranguo, A.I. and Gonzales, G.J., Prenyl flavanones oi Dalea caerulea. Rev. Columb. Quim., 23,... 

Souleles, C., A new prenylated flavanone from Melilotus alba, Set Pharm., 60, 10, 1992. 

Yenesew, A. et al.. Two prenylated flavanones from stem bark of Erythrina burttii. Phytochemistry, 48, 1439, 1998. 

Matsuura, N. et al., A prenylated flavanone from roots of Maackia amurensis subsp. buergeri. Phytochemistry, 36, 255, 1994. 

Seo, E.-K. et al., Cytotoxic prenylated flavanones from Monotes engleri, Phytochemistry, 45, 509, 1997. 

Lemos, V.S. et al.. Total assignments of and NMR spectra of a new prenylated flavanone from Dioclea grandiflora, Magn. Reson. Chem., 40, 793, 2002. 

Ferrari, F. and Messana, L, Prenylated flavanones from Sorocea ilicifolia. Phytochemistry, 38, 251, 1995. 

Rao et al. revised the structure of crotaramosmin (286), formerly described as a prenyl-flavanone, to 2, 4-dihydroxy-6",6"-dimethylpyrano[2",3" 4, 3 ]dihydrochalcone. Two derivatives of crotaramosmin, crotaramin (287) and crotin (292), were later isolated from the same source, Crotalaria ramosissima (cited incorrectly as Crotolaria ramosissima) Kanzo-nol Y (294) is an uncommon diprenylated a-hydroxydihydrochalcone found in cultivated licorice (Glycyrrhiza glabraf for which the absolute configuration was determined by... 

Glycyrrhiza glabra L. (hairy root cultures) Prenylbiaurone. Licoagrone (258). Ketalized prenyl flavanone-prenylisoflavan-. Licoagrodin (375). Asada et al., 1999[221] Li et al., 2000[222]. 

The mixture of compounds contained in the crude extract were separated by chromatography on silica gel using various organic solvents. This process led to the isolation of three chalcones, 11 prenylated flavanones, three pterocarpanoids and one isoflav-3-ene (Figure 3). While the details of the characterization of these compounds have been reported elsewhere, it is worth pointing out that in the bioassay assessment referred to above, they had reasonable LC50 values (Table 4). They had antimalarial activities comparable to those of the crude extracts and should be the principles responsible for the activity. 

We also re-investigated the cyclization reactions of 309 and 310. Both prenylflavanones gave dihydropyranoflavanones 311 and 312 but no 312 (Fig. 25). The substituent effect on the 5-OH signal of synthetic flavanones (309,310,313,314 and 315) agrees with the rule for the other prenylated flavanones as shown in Fig. 25. The difference in the chemical shift of such isomers, i.e., flavanones with a prenyl group at the 6- or 8-position, is considerable (0.32-0.39 ppm). Thus, the chemical... 

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