Flavonoids isolation

The K-R reaction has also been useful for structural confirmation of natural products such as tambulin (71), a flavonoid isolated from the seeds of Xanthoxylum acanthopodium In the critical reaction (O-ethoxyphloroacetophenone (72) was allowed to react with anisic anhydride (38b) in the presence of sodium anisate (73) at 170 C to deliver flavone 74 in 65% yield. Flavone 74 was then converted after multiple steps to diethyl ether 75 which corresponded to the diethyl ether of tambulin (71). 

Avallone R, Zanoli P, Puia G, Kleinschnitz M, Schreier P, Baraldi M. Pharmacological profile of apigenin, a flavonoid isolated from Matricaria chamomilla. Biochem Pharmacol 2000 59 1387-1394. 

Li J and Jiang Y. 2007. Litchi flavonoids isolation, identification and biological activity. Molecules 12(4) 745-758. 

Maruyama, H., Sumitou, Y., Sakamoto, T., Araki, Y. and Hara, H. (2009) Biol. Pharm. Bull., Antihypertensive effects of flavonoids isolated from Brazilian green propolis in spontaneously hypertensive rats, 32(7), 1244-1250. 

Rattanachaikunsopon P, Phumkhachom P. (2007) Basteriostatic effect of flavonoids isolated from leaves of Psidium guajava on fish pathogens. Fitoterapia 78 434 36. 

Na MK, Jang JP, Njamen D, Mbafor JT, Fomum ZT, Kim BY, Oh WK, Ahn JS. (2006) Protein tyrosine phosphatase-IB inhibitory activity of isoprenylated flavonoids isolated from Erythrina mildbraedii. J Nat Prod 69 1572-1576. 

Bastle, A. Giordano, S. Lopez-Saez, J.A. Cobianchi, R.C. (1999) Antibacterial activity of pure flavonoids isolated from mosses. Phytochemistiy, 52,1479-82. 

The aim of this chapter is not a detailed description of the technique and instrumentation but to show applications of HPLC in the preparative separation of flavonoids. Some representative examples are given in Table 1.1. In a 1982 review of isolation techniques for flavonoids, preparative HPLC had at that time not been fully exploited. However, the situation is now very different and 80% of all flavonoid isolations contain a HPLC step. Approximately 95% of reported HPLC applications are on octadecylsilyl phases. Both isocratic and gradient conditions are employed. 

Modern mass spectrometric techniques are very well suited for the analysis of flavonoids isolated from plants and foodstuffs and in their in vivo metabolite forms (Table 2.8). Progress during the last two decades has made MS the most sensitive method for molecular analysis of flavonoids. MS has the potential to yield information on the exact molecular mass, as well as on the structure and quantity of compounds with the nature and within the mass range of flavonoids. Furthermore, due to the high power of mass separation, very good selectivities can also be obtained. 

Li, Q.M. et al., Mass spectral characterization of C-glycosidic flavonoids isolated from a medicinal plant (Passiflora incarnata), J. Chromatogr., 562, 435, 1991. 

Table 1. Flavonoids isolated from Kyrgyz and European Glycyrrhiza glabra...

The low-molecular-weight water-soluble fraction of LCP flour was found by thin layer chromatographic methods to contain several flavonoid components. To establish the role of flavonoids in the production of yellow color in biscuits, these components were extracted from LCP and glandless cottonseed flours with 85Z aqueous isopropyl alcohol (which is a better solvent for flavonoids than water). Before removal of the flavonoids, the flours had been treated with petroleum ether to extract residual lipids that could interfere with flavonoid isolation. Extraction of the residual lipids did not significantly alter the color of biscuits prepared with the extracted flours (Figure 7). 

It was shown later that the streptomycete can only modify rather than biosynthesize these compounds [66] and that all such derivatives, i.e. even genisteins (64,65) come from the soy meal or cotton seed and are not produced by streptomycetes. These results demonstrate clearly that flavonoids isolated from streptomycetes cultivated on media containing plant components, such as soy meal or cotton seed, always come from the cultivation medium and are not of microbial origin. The same effect was observed in S. griseus [65] producing two additional chlorinated genisteins (66,67). This also holds true [67] for isoflavone (68) isolated from Japanese soil. 

Separation, purification and identification have yielded baicalein, baicalin and other Free-B-Ring flavonoids as the major active components in the organic extract from the roots of Scutellaria baicalensis, and S. orthocalyx. In Table 2, we demonstrated the potencies of five Free-B-Ring flavonoids isolated from three different Scutellaria species. 

Diprenyleriodictyol (83), the simplest diprenylated flavanone, is a citotoxic compound first reported by Harborne et al in 1993 from Vellozia coronata and V. nanuzae [66]. The structure of dorsmanine E (84) was established from analysis of the spectroscopic data for the presumed natural product as well by synthesizing it from 6, 8-diprenyleriodictyol (83) upon treatment of the latter with methanolic HC1. Dorsmanin B (85) [39] as dorspoinsettifolin (79) and 78 lack the 5-hydroxyl functionality that is common in most of the flavonoids isolated so far from Dorstenia spp and the range of compounds isolated from D. 

Iwli et al [97] have reports based on the evaluation of plant-extract of D. multiradiata for antileishmanial activity using a mechanism-based radiorespirometric micro-technique. Extracts were found to be active at concentrations of 50 pg/ml or less against a visceral leishmania isolate. A number of Dorstenia species used traditionally as anti-snake venom were subjected to a pharmacological screening process and were found to possess analgesic and anti-inflammatory activities [98]. Many of the flavonoids isolated from African Dorstenia show moderate to good antioxidant activities [Croft, unpublished results]. The cytotoxic properties of... 

Flavonoids isolated firom Astragalus spp. belong to the following classes of constituents flavones, flavonols, flavanones, isoflavones and isoflavans, all as aglycones than glycosides, and pterocarpans (Table 5). 

Structure analysis has been revealed that 6-hydroxylation of flavonols and flavones is a common feature in Tanacetum species. Flavonoids isolated from several Tanacetum species are represented in alphabetical order in Table 5 and their structures are shown in Fig. (1-3). 

Table 5. Flavonoids Isolated from Tanacetum Species...

Other species from the Artemisia genus also yielded antimicrobial flavonoids. Flavonoids isolated from the Polish medicinal herbs Artemisia molinieri, Artemisia selengensis Turcz. ex Bess, and Artemisia stolonifera (Maxim.) Kom. showed antifungal activity against some species of phytopathogenic fungi [219]. 

The antimicrobial activity of luteolin. Fig. (35), a flavonoid isolated from Wedelia paludosa was also evaluated [205]. The compound showed activity towards the dermatophytes Epidermophyton floccosum. Trichophyton rubrum and Trichophyton mentagrophytes. 

Several studies describe the hypnotie activity of flavonoids. Apigenin is a flavonoid that showed sedative and antidepressant activity [367]. The flavonoids and indole alkaloids of P. incarnata L., also showed sedative effects [368]. Linarin, a flavonoid-isolated from Valeriana officinalis L. showed sedative and sleep-enhancing properties (Fernandez et al., 2004). The nonvolatile fraction of L. alba, extracted in ethanol, presented sedative and myorelaxing effects among the extracts tested, these possess the highest flavonoid content [296]. 

Fig. (11). Chemical structure of flavonoids isolated from Slachys spruney (family Lamiaceae) quercetin (a) and its glycoside rutin (c), isoscutellarein (b) and its glycoside...

Sohn, H. Y. Son, K. H. Kwon, C. S. Kwon, G. S. Kang, S. S., Antimicrobial and cytotoxic activity of 18 prenylated flavonoids isolated from medicinal plants Moms alba L., Moms mongolica Schneider, Broussnetia papyrifera (L.) Vent, Sophora flavescens Ait and Echinosophora koreensis Nakai, Phytomedicine, 2004, 11, 666-672. 

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