Bioassay-guided

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... 

Parasitic hymenoptera hold promise in integrated pest management schemes, because they parasitize many economically important insect pests in a species-and stage-selective manner. The pheromones and kairomones of the parasitic hymenoptera have been studied for a long time, and there are many examples where there is evidence of chemical mediation of parasitoid behavior. This review emphasizes work done since the last major reviews [11, 12, 42] and, where it is available, on the primary bioassay-guided chemical identification of the semiochemical (Fig. 2 and Tables 3 and 4). 

In Alloxysta victrix, 6-methylhept-5-en-2-one 16, which is produced by both males and females, was identified as potentially attractive to the males and slightly repellent to the females in Y-tube olfactometer assays [60]. In this study, the activity was also dependent on prior exposure of the insects to the compound. Naive insects responded more strongly than previously exposed ones. This underscores a second difficulty in the bioassay-guided identification of parasitoid hymenopteran pheromones the responses are very dependent on the context and on prior exposure. Learning has been demonstrated in several species of parasitic hymenoptera [61-65]. 

One example for a chemically defended zooplankton species is the Antarctic pteropod Clione antarctica. This shell-less pelagic mollusk offers a potentially rich source of nutrients to planktivorous predators. Nonetheless fish do not prey on this organism, due to its efficient chemical defense. In a bioassay-guided structure elucidation, pteroenone 37 could be isolated and characterized as the main defensive principle of C. antarctica [82,83]. If embedded in alginate, this compound is a feeding-deterrent in nanomolar concentrations. This unusual metabolite is likely to be produced by C. antarctica itself and not accumulated from its food, since its major food sources did not contain any detectable quantities of 37. 

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. 

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