2.  Used extensively in relation with drug discovery  Principle of Combinatorial Chemistry ◦ Generation of Compound Libraries from Molecular Building blocks

3.  Establishment of Libraries ◦ Unbiased libraries  Typically a common chemical core (starting point scaffold)  Large number og building blocks  Generating ”lead” structures ◦ Directed libraries  Again a common chemical core  Limited number of building blocks  Directed towards a specific target  Used to optimize ”lead” structures

4.  Product is Linked to a Solid Support ◦ Easy removal of excess reagents through filtration ◦ Dendrimer and poly ethylene glycol resins has been developed to improve the yield

5.  Reaction proceeds in Solution ◦ Faster validation times relative to solid phase synthesis ◦ Standard analytical protocols can be used to characterize products between each reaction step

6.  Solid phase synthesis + Easy purification -Low yield, Tagged at the point of attachment, Dificult to apply standard characterization methods on intermediates  Solution phase synthesis + Easy characterization of intermediates as well as end pruduct, No limitations in attachment point. - Difficult to drive the reaction towards the product, extensive purification is needed

7.  Polymer-supported reagents and scavangers ◦ Hybrid between solid and solution phase synthesis ◦ Reagents and scavangers are brougth to the reaction on solid supports

8.  Parallel Synthesis ◦ Each compund is prepared in a specific vessel ◦ Array of reaction vessels ◦ Automated control of reactions

9.  Pool/Split Synthesis ◦ Beads are split into different vessels ◦ Then reacted, shuffled, and split again. ◦ 1000 compund library prepared from 10 building blocks in each step  30 reaction steps. (1110 steps for parallel synthesis)

10.  Radio Frequency (RF) tagging ◦ Transponder tags incase in porous glass beads with a loading capacity of 30-300 mg of resin beads  Nano tagging ◦ One reacent development in the labeling of beads is the nano-reactors these are labled with 2D- barcodes making it possible to keep track of libraries with up to 100,000

11.  Parallel synthesis + Easy to keep track of each compund, High yield - Large libraries takes manny reaction steps  Pool/Split + Large libraries are prepared through a limited number of reaction steps - Labelign are required to keep track of each compound

12.  Liquid-Liquid extraction ◦ Extensivley used for solution-phase combinatorial synthesis. ◦ Automated by frezing liquid phase. Extraction Techniques for Purification  Fails when; ◦ Emulsions form ◦ The impurities have the same solubility properties

13.  Fluorous phase technique ◦ Attach a insoluble perfluorinated moiety to the compound. ◦ Retain the molecules from fluorous solvent.  Solid-phase extraction ◦ Based on adsorption to a suitable surfacesurface. ◦ Impurities are washed away with a solvent where in the compound are insoluble.

14.  Combinatorial Libraries vary in size, amount, purity and structual complexity  The libraries can be devided into 3 groups ◦ 1: One-bead one-compound ◦ 2: Preencoded libraries ◦ 3: Spatially addressable libraries

16.  1991-2003; ~2500 libraries  ”Unbiased libraries”; 1-2 million compounds  Screening does not always result in hits. ◦ ”Directed libraries” build on a privileged structure” ◦ Libraries based on a modelling.

17.  By screening pool/split solid-phase library of 128 000 2-arylindoles (1) split split into 320 pools of 400 compounds and screened against16 G-protein coupled receptor targets ◦ Some pools both active and selective  Compund 2 higly selective for Natural Killer Cell receptors, therefore viable lead for medical chemitsry

18. Lead Identification vs. Lead Optimization  Lead identification libraries < 10 000  Lead optimization libraries 1000-2000  Lead optimization via focussed libraries based on a privileged structure  Both solution and solid-phase synthesis

19.  Solid phase synthesis with RF tagging  Screening of ~650 000 compounds  28; active in a human erythropoietin (EPO) assay and have phosphodiesterase 3 activity  32; treatment of anemia