Bioassay guided fractionation

Only a few studies have reported the antiprotozoal activity of proantho-cyanidins. Bioassay-guided fractioning of the extract of Geranium niveum led to the isolation of two new A-type proanthocyanidins epf-afzelechin-(4j6 8,2j6 0 7)-afzelechin and EC-(4/l 8,2/1 0 7)-afzelechin... 

A survey of current available chemical data, suggests that methylated flavones and, to a lesser extent flavonols, frequently aglycones, are the main classes of antimicrobial and antiviral flavonoids found in medicinal plants. Some of these compounds have been isolated by bioassay-guided fractionation, after previously detecting activity on the part of the plant. 

Zeyheria tuberculosa (Veil.) Bur. (Bignoniaceae) is a species used in Brazilian folk medicine for the treatment of cancer and skin diseases. From the extracts of this plant, four flavones namely 5,6,7,8-tetramethoxyflavone, 5,6,7-trimethoxyflavone, 4 -hydroxy-5,6,7,8-tetramethoxyflavone and 4 -hydroxy-5,6,7-trimethoxyflavone, were isolated through bioassay-guided fractionation and evaluated for in vitro antimicrobial activity. These results showed that isolated flavones may be particularly useful against two pathogenic microorganisms. Staphylococcus aureus and Candida albicans, which may justify the popular use of this species. 

In order to identify novel lead compounds with antiviral effects, methanol and aqueous extracts of some medicinal plants in the Zingiberaceae family were screened for inhibition of proteases from human immunodeficiency virus type 1 (HIV-1), hepatitis C virus (HCV) and human cytomegalovirus (HCMV). By bioassay-guided fractionation, eight fiavones were isolated from the black rhizomes of Kaempferia parviflora Wall, ex Baker. The most effective inhibitors, 5-hydroxy-7-methoxyfiavone and 5,7-dimethoxyflavone, inhibited HIV-1 protease, with an inhibitory concentration 50 (IC50) values of 19 0,M. Moreover, 5-hydroxy-3,7-dimethoxyflavone inhibited HCV protease and HCMV protease, with IC50 values of 190 and 250 pM, respectively. 

Eine, J. M. and Sorensen, P. W. (2004). Bioassay-guided fractionation demonstrates that the sea lamprey migratory pheromone is a mixture of at least three sulfated steroids. lnAnnualMeetingoflnternationalSocietyofChemicalEcology,July 2004, Ottawa, Canada. 

Numerous additional examples of the evaluation of plant essential oils as insect repellents exist in the literature however, rarely are bioassay-guided fractionations performed to determine the constituents responsible for the activity of these plant essential oils. When attempts are made to identify active constituents, they are often of a non-systematic manner and usually focus on those constituents that are commercially available or the major constituents. Such approaches have the potential of missing unusual or novel structural types which could be highly active compounds with the potential for commercial development. 

Bioassay-guided fractionation of a phytotoxic extract led to the isolation of two major phytotoxic agents (Fig. 8) characterized as 2 -(2 -hydroxy-4 -methylphenyl)-2 -oxoethyl acetate and designated with the trivial names of hofmeisterin (29) and 3 4 4tz 9rz -tetrahydro-6,7 -dimethylspiro [benzofuran-3(2//), 2 -pyrano [2, 3- ] benzofuran]-2, Aa -diol (30), along with several inactive compounds. 

The bioassay-guided fractionation of the extracts of Plumeria rubra barks also proved to be a successful strategy, leading to the isolation of eleven substances, of which eight were iridoids. In this context, the aqueous extract of Plumeria rubra bark has iridoids such as the epimers, a-allamcidin and (l-allamcidin, which were resolved by preparative TLC on Si-gel G plates (20 x 20 cm, 250 pm, Merck ), using chloroform/ethyl acetate/methanol (3 3 1) as solvent system [44]. 

---