Radical Reactions in Combinatorial Chemistry

Organic synthesis is dominated by polar transformations, in which an electron-rich center reacts with an electron-deficient center. By contrast, homolytic processes involving organic radicals were largely unexploited for many years. The general belief was that such ''free radicals'' would be undisciplined in their reactions, and prone to undesirable pathways such as premature radical-radical recombination or hydrogen atom abstraction from the solvent. Even under successful chain-propagating...

Electrophilic Substitution in Combinatorial and Solidphase Synthesis

Jan-Gerd Hansel and Stephan Jordan 9.1 Reactions in which an electron-deficient reagent attacks a substrate and an electron-deficient leaving group is displaced are called electrophilic substitutions (SE). The most common leaving group is the proton. While the reaction is typical for aromatic systems, aliphatic substrates only react when hydrogens of sufficient acidity are available. This chapter focuses on the application of SE in the generation of chemical diversity. Compared with...

Analysis of Combinatorial Libraries

Combinatorial syntheses need fast and reliable analyses in order to determine the identity of products and intermediates in each step of a parallel reaction sequence. 6.3 Analysis of Combinatorial Libraries 217 Tab. 6.5. Analytical methods and their applications in combinatorial chemistry. Method Application FT-IR Characterization of resin-bound intermediates in reflection (ATR (ATR attenuated total reflectance) DRIFTS (DRIFTS diffuse reflectance infrared fourier transform spectroscopy)) NMR...

Radiofrequency Tags

Microreactor System

One of the most successful automated solutions for the synthesis of encoded chemical libraries is utilizing electronic identification devices. Scheme 5.12 illustrates one such device - the radiofrequency RF identification ID tag. Similar Rectifier Trarumitter feceiver circuitry Scheme 5.12. Schematic of an RF memory chip useful for encoded synthesis. Scheme 5.12. Schematic of an RF memory chip useful for encoded synthesis. devices have been used for years to tag laboratory mice subcutaneously,...

Privileged Structures

The term ''privileged structures'' was introduced by Evans and coworkers for structural types of small molecules that are able to bind with high affinity to multiple classes of receptors 42 . Benzazepine analogs were found to be effective ligands for 768 27 Virtual Compound Libraries and Molecular Modeling Tab. 27.1. GPCR-like building blocks. Structurea GPCR likeness Structure Structure Structurea GPCR likeness Structure Structure a Building blocks were taken from the Available Chemicals...

OnVyn2 1sclg2H20NMP oW

Synthesis of a benzimidazole library via tin-mediated nitro reduction. cally accompany nitro reduction with SnCl2, which presents a potential problem with acid-sensitive polymer supports. Addition of a small amount of buffer such as sodium acetate often remedies this situation 35, 115 . DMF is the solvent of choice for tin reductions, but N-formylation of o-diaminobenzenes generated from 2-amino-substituted nitrobenzenes and subsequent cyclization to benzimidazoles has been...

Nucleophilic Substitution in Combinatorial and Solidphase Synthesis

Jan-Gerd Hansel and Stephan Jordan 8.1 Nucleophilic substitution SN reactions are widely used in combinatorial chemistry. Two reasons account for this prevalence first the potential to combine building blocks by SN and second the availability of building blocks that can participate in SN reactions. In addition, SN reactions are typically very reliable transformations, robust, and thus ideally suited for high-throughput synthesis of organic compounds. In this chapter the application of SN...