Poterat and Hamburge Complexation Polymerisation with template reviewed by Xu and Chen [73].Molecular imprinted e (28)was used to identify harmine of e (SPE)of plant extracts or [79. nclude the preparative ration of matrine (25)from the inhibitors of the hepatitisC virus NS3 protease in a 761 The oids from ngko biloba leaves [77]. 36 of the template molecu often als fit into the rated and identified.These data were in or o ucturally related MIPs are suited for bio ed as a t to o new MS-BASED METHODS from and ctivi har mplate qu for drug di h e MIP natrine (25 0. harmaline (30) 910 Current Organic Chemistry, 2006, Vol. 10, No. 8 Potterat and Hamburger reviewed by Xu and Chen [73]. Molecular imprinted polymers (MIP) are well suited for a selective trapping of target molecules in complex matrices. Solid phase extraction (SPE) of various compounds from plant extracts or biological fluids has been reported. Typical examples include the preparative separation of matrine (25) from the Chinese medicinal plant Sophora flavescens Ait (Leguminosae) [76], and the selective extraction of flavonoids from Gingko biloba leaves [77]. A particularly interesting feature of molecular imprinting is that structural analoges of the template molecule often also fit into the imprinted cavities. Thus, a known inhibitor of a receptor or an enzyme can be used as template to screen for unknown structurally related inhibitors. In a representative example of this approach, quercetin (20), a known protein tyrosine kinase inhibitor was used as a template to search for inhibitors of the epidermal growth factor (EGFR) in Caragana jubata (Pall.) Poir. (Leguminosae), a traditional Tibetan medicine [78]. Two new inhibitors, (E)-piceatannol (26) (IC50 = 4.5 mM) and butein (27) (IC50 10 mM) could be selectively separated from the EtOAc extract, and were shown to be the main active constituents of the extract. Interestingly, both compounds exhibited stronger activity than the template quercetin itself (IC50 = 15 mM). Molecular imprinted stationary phases have been used in analytical chromatographic and electrophoretic separation systems as well. A LC-MS system equipped with a MIP column imprinted with harmane (28) was used to identify harmine (29) and harmaline (30) as the antitumor components from the methanolic extract of Peganum nigellastrum Bunge (Zygophyllaceae) seeds [79]. In another example, LC separation on MIP phases enabled to selectively trap inhibitors of the hepatitis C virus NS3 protease in a crude extract of Phyllanthus urinaria L. (Euphorbiaceae). The known inhibitor RD3-4078 (31) was used as a template, and ellagic acid (32), corilagin (33), geraniin (34), phyllanthusiin U (35) and 1,3,6-tri-O-galloyl-b-D-glucose (36) were selectively separated and identified. These data were in good agreement with results obtained with frontal immunoaffinity chromatography (see below) [80]. In the form of thin films, MIPs are well suited for biosensor applications. In a recent example, a biomimetic covalently imprinted polymeric sensor with subpicomolar affinity has been developed for the d-opioid G-protein coupled receptor agonist [D-Pen2 , D￾Pen5 ] enkephalin [81]. MS-BASED METHODS A growing number of MS-based approaches taking advantage of the selectivity and high affinity of macromolecule-ligand interactions have been proposed as alternative screening methods for drug discovery. The developments in this field have been recently discussed in an excellent review which pays attention to both the technical aspects and the potential of the respective methods as tools Fig. (8). Outline of the molecular imprinting process. (Adapted from [82]; © 2002 Kluwer Academic Publishers with kind permission of Springer Science and Business Media). N N O H H H matrine (25) HO OH OH OH (E)-piceatannol (26) OH O OH OH HO butein (27) N H N O harmaline (30) N H N R R = H harmane (28) R = OMe harmine (29)