Split-and-mix Libraries

Split-and-mix libraries have found numerous applications in the search for a substrate for a given receptor and vice versa. A typical affinity assay encompasses labeling of the host of interest with, e.g., a dye, a fluorophore, or radioactivity and equilibrating the labeled host with the bead-supported library of potential guests. The labeled host will be concentrated by those beads that carry molecules with affinity for the receptor. These beads are easily identified by visual inspection of the assay under a low-power microscope. Isolation and structural analysis reveals the structure of the active compound [3]. Recently, split-and-mix libraries are also successfully applied in the search for catalysts (see Chapter 5.4). 

In parallel libraries each compound is located in a defined reaction container, for example, one well of a 96-well plate. Because the molecular diversity of split-and-mix libraries usually exceeds that of parallel libraries, many more potential catalysts can be tested in split-and-mix libraries. Their screening is, however, a much greater challenge if the ensemble of all the beads is tested simultaneously. In contrast to parallel libraries, in which each potential catalyst is located in a defined reaction container, reactants and products are free to diffuse in the solvent that surrounds all the beads and leave the catalyst - naturally - unchanged. The challenge has been met by ... 

Testing of Split-and-mix Libraries for Catalytic Activity 440 5.4.3.1 IR-thermography 440... 

One other application of such monoliths, for the S5mthesis of a split and mix library, was presented by Janda (115). The preparation of euclidean-shape monoliths was performed using a monomer mixture of styrene, chlroromethylstyrene, and 1,4- bis(vinylphenoxy)butane as cross-linker. Dodecanol was used as inert diluent and benzoyl peroxide as initiator. 

Mmray JK, Sadowsky JD, Scalf M et al (2008) Exploration of structure—activity relationships among foldamer ligands for a specific protein binding site via parallel and split-and-mix library synthesis. J Comb Chem 10 204-215... 

The solid-phase technique of split and mix synthesis relies on the efficiency of mixture-based synthesis to provide very large libraries (millions) of discrete compounds (Figure 4).[161 In this approach, each resin bead is treated with a single building block for each synthesis step. Thus any single resin bead possesses identical copies of one library member, but the identity of the library member on any bead is lost due to the mix step of the process. Elegant strategies have been developed to chemically encode the syn-... 

Solution-phase library Resin scavenging Resin capture Split and mix... 

This dendritic support (1) was used to generate a library of indole derivatives with three centers of diversity following the Fischer protocol and the split and mix strategy. One example of this sequence is outlined in Scheme 7.1. 

In Section II.C we will present novel tricyclic xanthene derived amino acid templates, which allow the construction of libraries of cyclic conformationally constrained peptide loop mimetics using the split-and-mix method without having to use tagging and deconvolution strategies. In Section III we will focus on parallel and combinatorial approaches devoted to the synthesis of small molecule, non-peptidic compound collections, which in addition offer the possibility to incorporate structural features derived from protein epitope mapping into conformationally constrained peptide mimetics. 

As shown in template 91, a linker group can be attached to the tricyclic skeleton which results in the possibility to graft the template onto a solid support and synthesize template-bridged cyclic petide libraries using the split-and-mix method. 

Combinatorial synthesis on solid supports is usually carried out by using either the parallel synthesis (see section 6.2.1) or the Furka split and mix procedures (see section 6.2.2). The precise method and approach adopted when using these methods will depend on the nature of the combinatorial library being produced and also the objectives of the investigating team. However, in all cases it is necessary to determine the structures of the components of the library by either keeping a detailed record of the steps involved in the synthesis or giving beads a label that can be decoded to give the structure of the compound attached to that bead (see section 6.3). The method adopted to identify the components of the library will depend on the nature of the synthesis. 

Taylor and Morken extended the use of IR-thermography to the monitoring of the change in the heat of reaction on and in the surroundings of a bead carrying an active catalyst (Figure 5.4.4) [13]. In a search for acylation catalysts an encoded library of 3150 different potential nucleophilic catalysts was prepared by the split-and-mix procedure and tested for their acylation properties. The library beads were spread in a reaction solution of chloroform-ethanol-triethylamine-acetic anhydride, 40 6 6 3, and monitored with an IR camera. Whereas no detectable thermal... 

Combinatorial chemistry is the production of libraries of compounds that represent permutations of a set of chemical variables. These variables include the nature of the substituent in a particular molecule, both in type and size, changes in the components in a mixture of materials, e.g. in ceramics and changes in process parameters, e.g. temperature, pH etc. Chemical libraries are usually created by one of two methods split and mix or parallel synthesis . Split and mix synthesis is used to produce small quantities of a relatively large number of compounds and requires assays to be performed on pools of compounds. Parallel synthesis is used to produce libraries... 

In this chapter we will discuss current approaches for analytical characterization of combinatorial libraries in a pharmaceutical industry environment. Recently, several analytical groups have presented very similar strategies for analysis of libraries [7-9]. As will be shown later, the key to successful analytical characterization of a combinatorial library is to perform analytical and chemical work in parallel with the library development. The accumulation of data and analytical experience during this process results in an assessment of library quality with a high level of confidence, even if as little as 5-10% of the library components are analyzed. Utilization of the strategy will be demonstrated using two examples analysis of a library synthesized on a robotic station in spatially addressed format and analysis of a library synthesized in accordance with split-and-mix technology. 

---