Small molecule modulators of biological function can be discovered by the screening of compound libraries. However, it became apparent that some human disease related targets could not be addressed by the libraries commonly used which typically are comprised of large numbers of structurally similar compounds. The last decade has seen a paradigm shift in library construction, with particular emphasis now being placed on increasing a library's structural, and thus functional diversity, rather than only its size. Diversity-oriented synthesis (DOS) aims to generate such structural diversity efficiently. This tutorial review has been written to introduce the subject to a broad audience and recent achievements in both the preparation and the screening of structurally diverse compound collections against so-called 'undruggable' targets are highlighted.

A prerequisite for successful screening campaigns in drug discovery or chemical genetics is the availability of structurally and thus functionally diverse compound libraries. Diversity-oriented synthesis (DOS) provides strategies for the generation of such libraries, of which the build/couple/pair (B/C/P) algorithm is the most frequently used. We have developed an advanced B/C/P strategy that incorporates multidimensional coupling. In this approach, structural diversity is not only defined by the nature of the building blocks employed, but also by the linking motif installed during the coupling reaction. We applied this step-efficient approach in a DOS of a library that consisted of 73 macrocyclic compounds based around 59 discrete scaffolds. The macrocycles prepared cover a broad range of different molecular shapes, as illustrated by principal moment-of-inertia analysis. This demonstrates the capability of the advanced B/C/P strategy using multidimensional coupling for the preparation of structurally diverse compound collections.

Syntheses under microwave irradiation were performed in sealed tubes using a Biotage AB SmithSynthesizer. TLC was performed on Merck Silica Gel 60 F 254 aluminum sheets. Reagents used for developing plates include Cer-Reagent (5 g molybdatophosphoric acid, 2.5 g ceric sulphate tetrahydrate, 25 ml sulfuric acid and 225 ml water), ethanolic ninhydrine (3 % w/v), ethanolic sulfuric acid (15 % v/v) and detection by UV light was used when applicable. Flash column chromatography was performed on Macherey-Nagel Silica Gel 60 (0.04 -0.063 mm; 230 -400 mesh ASTM). Combustion elemental analyses were performed on an elementar vario EL analyzer.Warning: In the case of reactions with azide sources in dichloromethane, formation of explosive diazidomethane has been reported.1 Therefore, the triflyl azide solution in dichloromethane should always be prepared freshly and the reaction time of 2 h should not be exceeded. Special caution should also be exercised during the workup procedure (especially during evaporation of the reaction mixture) due to excess triflyl azide and possibly formed copper azides, although we never observed any incident. General Procedure 1: Sequential One-Pot Process for Diazo Transfer and Azide-Alkyne Cycloaddition Using CuSO 4 and Sodium AscorbateTriflyl azide (TfN 3 ) was freshly prepared prior to each reaction. 2 NaN 3 (6 eq per substrate amine) was dissolved in a minimum volume of water (solubility of NaN 3 in water is approximately 0.4 g/ml). At 0 °C an equal volume of dichloromethane was added and triflic anhydride (Tf 2 O) (3 eq) was added dropwise to the vigorously stirred solution. After stirring for 2 h at 0 °C the aqueous phase was onceKonstanzer Online-Publikations-System (KOPS)

Carbohydrate microarrays are an emerging tool for the high-throughput screening of carbohydrate-protein interactions that represent the basis of many biologically and medicinally relevant processes. The crucial step in the preparation of carbohydrate arrays is the attachment of carbohydrate probes to the surface. We examined the Diels-Alder reaction with inverse-electron-demand (DARinv) as an irreversible, chemoselective ligation reaction for that purpose. After having shown the efficiency of the DARinv in solution, we prepared a series of carbohydrate-dienophile conjugates that were printed onto tetrazine-modified glass slides. Binding experiments with fluorescently labeled lectins proved successful and homogeneous immobilization was achieved by the DARinv. For immobilization of nonfunctionalized reducing oligosaccharides we developed a bifunctional chemoselective linker that enabled the attachment of a dienophile tag to the oligosaccharides through oxime ligation. The conjugates obtained were successfully immobilized on glass slides. The presented strategies for the immobilization of both synthetic carbohydrate derivatives and unprotected reducing oligosaccharides facilitate the preparation of high-quality carbohydrate microarrays by means of the chemoselective DARinv. This concept can be readily adapted for the preparation of other biomolecule arrays.

Bulky amino acids in positions 2 and 3 of proteins protect both Met and noncanonical azidohomoalanine, introduced by the auxotrophy‐based method, from being excised by the enzymes responsible for N‐terminal Met excision. Bioorthogonal transformation enables new specific functionalization of target proteins. We validated this general concept by designing an N‐terminal glycoconjugated barstar capable of lectin binding without losing its biological activity.

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Macrocyclic compounds represent a structural class with exceptional potential for biological activity; however, they have historically been underrepresented in screening collections and synthetic libraries. In this article we report the development of a highly step-efficient strategy for the diversity-oriented synthesis of complex macrocyclic architectures, using a modular approach based on the two-directional synthesis of bifunctional linear precursors and their subsequent combination in a two-directional macrocyclisation process. In this proof of principle study, the synthesis of 14 such compounds was achieved. Cheminformatic analysis of the compounds produced suggests that they reside in biologically relevant regions of chemical space and the compounds were screened for activity against two cancer cell lines.

SummaryA series of six mono-, di-, and trivalent N,N’-diacetylchitobiose derivatives was conveniently prepared by employing a one-pot procedure for Cu(II)-catalyzed diazo transfer and Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) starting from commercially available amines. These glycoclusters were probed for their binding potencies to the plant lectin wheat germ agglutinin (WGA) from Triticum vulgaris by an enzyme-linked lectin assay (ELLA) employing covalently immobilized N-acetylglucosamine (GlcNAc) as a reference ligand. IC50 values were in the low micromolar/high nanomolar range, depending on the linker between the two disaccharides. Binding enhancements β up to 1000 for the divalent ligands and 2800 for a trivalent WGA ligand, compared to N,N’-diacetylchitobiose as the corresponding monovalent ligand, were observed. Molecular modeling studies, in which the chitobiose moieties were fitted into crystallographically determined binding sites of WGA, correlate the binding enhancements of the multivalent ligands with their ability to bind to the protein in a chelating mode. The best WGA ligand is a trivalent cluster with an IC50 value of 220 nM. Calculated per mol of contained chitobiose, this is the best WGA ligand known so far.