Potterut and H epibatidine(15】 piquinamide(16) HPLC-BASED ON-FLOW BIOASSAYS ension to the reader [55]. 906 Current Organic Chemistry, 2006, Vol. 10, No. 8 Potterat and Hamburger HPLC-based activity profiling has been also recently reported for the search of new radical scavengers and antibacterial compounds. Scavenging activity was detected with the stable DPPH radical, while antimicrobial properties were assayed against Streptococcus pyrogenes. After lyophilization, the chemical reagent and the bacterial suspension, respectively, were directly added to the microplate. UV absorbance of DPPH and turbidity resulting from bacterial growth were measured using a microplate reader [55]. HPLC-BASED ON-FLOW BIOASSAYS A particularly remarkable line of development has been in the field of continuous-flow bioassays capable of detecting the desired biological activity directly in the HPLC effluent. Most of the work in this area has been carried out at the University of Amsterdam in close collaboration with the biotech company Kiadis (formerly Screentec) in Leiden. The numerous assay formats, which have been implemented, have been comprehensively reviewed by van Elswijk and Irth [56]. In this technology, complex mixtures such as R1 = R2 = H R1 = H R2 = OH R1 = R2 = OH 10 11 12 NH HN HN N HN HN HN NH HN N O O O O O O O O O NH NH2 OH O HN HO O NH HN N NH N HN N H NH HN O O O O O O O O O O N H S OH S O HO O OH OH OH O O O O OH OH HO OH OH O O O HO OH OH O HO O OH OH R1 R2 7 resistomycin (9) cephalochromin (8) 13 N H HO H O OH 14 H N NH Cl epibatidine (15) N HN O H epiquinamide (16)