Bioassay-guided fractionation of the hexane/ethyl acetate/water (H/EtOAc/H2O) crude extract of the aerial parts of Haplophyllum sieversii was performed because of preliminary screening data that indicated the presence of growth inhibitory components against Colletotrichum fragariae, Colletotrichum gloeosporioides, and Colletotrichum acutatum. Fractionation was directed using bioautographical methods resulting in the isolation of the bioactive alkaloids flindersine, anhydroevoxine, haplamine, and a lignan eudesmin. These four compounds were evaluated for activity against C. fragariae, C. gloeosporioides, C. acutatum, Botrytis cinerea, Fusarium oxysporum, and Phomopsis obscurans in a dose-response growth-inhibitory bioassay at 50.0, 100.0, and 150.0 microM. Of the four compounds tested, flindersine demonstrated the highest level of antifungal activity. Additionally, flindersine, eudesmin, and haplamine were screened against the freshwater phytoplanktons Oscillatoria perornata, Oscillatoria agardhii, Selenastrum capricornutum, and Pseudanabaena sp. (strain LW397). Haplamine demonstrated selective inhibition against the odor-producing cyanobacterium O. perornata compared to the activity against the green alga S. capricornutum, with lowest observed effect concentration values of 1.0 and 10.0 microM, respectively.

Columnaris disease, enteric septicemia of catfish, and streptococcosis are common bacterial diseases of certain freshwater fish and are caused by Flavobacterium columnare , Edwardsiella ictaluri , and Streptococcus iniae , respectively. During the process of evaluating several species of plants to isolate and identify compounds with toxicity against these bacteria, a promising extract from the aerial parts of the terrestrial plant Atraphaxis laetevirens (Ledeb.) Jaub. et Spach (Polygonaceae Juss.) was selected for bioassay-guided fractionation using a rapid microplate bioassay. The active dichloromethane extract was subjected to liquid-liquid partitioning, and active fractions were further separated by normal-phase column chromatography and normal-phase high-performance liquid chromatography (HPLC). Nepodin (3) and emodin (4) were isolated from two fractions with strong toxicities against S. iniae . A chloroform fraction was further separated by normal-phase column chromatography to yield two active fractions against F. columnare , and these fractions contained chrysophanol (1), physcion (2), and nepodin (3). Compound 1 had strong activity, and compound 3 had moderate activity against F. columnare , while compounds 2 and 4 were not toxic at the concentrations tested.

Four diterpenes with biological activity were isolated from Salvia deserta roots. Taxodione was considered leishmanicidal with an IC50 value of 1.46 µM (0.46 mg/L) against Leishmania donovani and also exhibited antifungal and antimicrobial activities. Ferruginol displayed the greatest activity [24-h IC50 of 4.5 µM (1.29 mg/L)] against the fish pathogenic bacteria Streptococcus iniae. The crude extract fraction that contained the isolated compounds 7-O-acetylhorminone and horminone showed stronger in vitro antibacterial activity (1.3 mg/L for Staphylococcus aureus and 1.1 mg/L for methicillin-resistant S. aureus) than the compounds tested alone. 7-O-Acetylhorminone and horminone exhibited a synergistic effect against methicillin-resistant S. aureus (FIC of 0.2), and horminone had better activity against S. aureus with respect to other compounds isolated from S. deserta roots. In larvicidal bioassays, these extracts and isolated pure compounds did not show any activity at the highest dose of 125 mg/L against 1-d-old Aedes aegypti larvae.

Over 70 crude plant extracts, primarily from Kazakhstan, were screened against the freshwater phytoplanktons Oscillatoria perornata and Selenastrum capricornutum. Extracts from Limonium myrianthum and Inula helenium both demonstrated selective inhibition against the odorproducing cyanobacterium O. perornata compared to activity against the green alga S. capricornutum. Bioassay-guided fractionation of the L. myrianthum dichloromethane extract resulted in the identification of nepodin, torachrysone, chrysophanol, and physcion. Nepodin demonstrated the desired selective inhibition with lowest-complete-inhibition concentration values of 100 µg/mL and >100 µg/mL towards O. perornata and S. capricornutum, respectively. Similarly, chrysophanol also demonstrated the desired selective inhibition with lowest-completeinhibition concentration values of 10 µg/mL and >100 µg/mL, respectively. Bioassay-guided fractionation of the I. helenium hexane extract resulted in the isolation of alantolactone, isoalantolactone, and 11αH,13-dihydroisoalantolactone. Activities of these three isolated constituents as well as those of synthetic isomers are reported.