Mixture-based synthetic combinatorial libraries

Appel, J.R., Johnson, )., Narayanan, V.L., and Houghten, R.A. Identification of novel antitumor agents from mixture-based synthetic combinatorial libraries using cell-based assays. Mol Div. 1999, 4, 91-102. 

Preparation of Mixture-Based Synthetic Combinatorial Libraries... 

Two major techniques are generally employed in solid-phase chemistry to generate mixture-based synthetic combinatorial libraries (SCL) of millions of compounds. Multiple functionalities at diverse positions within the library are incorporated either by mixing multiple resins or by using mixtures of incoming reagents. 

Generally, when developing a mixture-based synthetic combinatorial library, reaction conditions for all the steps in the reaction scheme need to be optimized to achieve the widest possible breadth of diversity and... 

Nefzi A, Ostresh JM, Yu Y, Maggiora GM, Medina-Franco JL, 46. Brunner D, Schneider J. Strategies for the use of mixture-based synthetic combinatorial libraries scaffold ranking, direct testing 47. in vivo, and enhanced deconvolution by computational methods. 

Mixture-based synthetic combinatorial libraries. J Med Chem 42 3743-3778... 

Richard A. Houghten, Darcy B. Wilson and Clemencia Pinilla, Drug discovery and vaccine development using mixture-based synthetic combinatorial libraries. Drug Discovery Today, 5 (2000), 276—285. 

Houghten, R.A., Pinilla, C., Giulianotti, M.A., Appel, J.R., Dooley, C.T., Nefei, A., Ostresh, J.M., Yu, Y., Maggiora, G.M., Medina-Franco, J.L., Brunner, D., and Schneider, J. (2008) Strategies for the use of mixture-based synthetic combinatorial libraries scaffold ranking, direct testing in vivo, and enhanced deconvolution by computational methods. Journal of Combinatorial Chemistry, 10,3-19. 

Finally, libraries aimed to chiral resolution of racemates will be covered here in particular, the use of chiral stationary phases (CSPs) has recently been reported for the identification of materials to be used for chiral separation of racemates by HPLC. The group of Frechet reported the selection of two macroporous poly methacrylate-supported 4-aryl-1,4-dihydropyrimidines (DHPs) as CSPs for the separation of amino acid, anti-inflammatory drugs, and DHP racemates from an 140-member discrete DHP library (214,215) as well as a deconvolutive approach for the identification of the best selector phase from a 36-member pool library of macroporous polymethacrylate-grafted amino acid anilides (216,217). Welch and co-workers (218,219) reported the selection of the best CSP for the separation of a racemic amino acid amide from a 50-member discrete dipeptide iV-3,5-dinitrobenzoyl amide hbrary and the follow-up, focused 71-member library (220). Wang and Li (221) reported the synthesis and the Circular Dichroism- (CD) based screening of a 16-member library of CSPs for the HPLC resolution of a leucine ester. Welch et al. recentiy reviewed the field of combinatorial libraries for the discovery of novel CSPs (222). Dyer et al. (223) reported an automated synthetic and screening procedure based on Differential Scanning Calorimetry (DSC) for the selection of chiral diastereomeric salts to resolve racemic mixtures by crystallization. Clark Still rejxrrted another example which is discussed in detail in Section 9.5.4. 

As for all synthetic products to be tested in biological systems, a careful analytical characterization of peptide libraries is crucial in order to confirm their identity and establish their quality. Compared to individual peptides, however, the analysis of peptide libraries is complicated due to the fact that the peptides are either bound to a solid support or arranged in highly complex mixtures. This poses certain restrictions on which analytical methods can be used to characterize combinatorial libraries. For example, analytical methods that are based on the separation of product components, such as high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), are only of limited use for the analysis of peptide libraries, in particular of those made up of complex nnixtures (>100 peptides per mixture). The analytical methods beneficially applicable to peptide libraries include amino acid analysis, mass spectrometry, and sequencing. 

If combinatorial libraries consist of compound mixtures (e.g., after cleavage from the resin beads), a reliable analytical characterization is difficult. In this case the utilization of mass spectrometry for analysis is based on the prediction of mass distribution of the library. Computer-generated distribution profiles can be compared with the actual profile obtained from the compound library [93,94]. Evaluation of mass distribution detects synthetic problems based on incomplete coupling (shift toward lower molecular masses), incomplete deprotection, or unwanted library modification, such as oxidation, acylation, or alkylation (shift toward higher molecular masses). However, for a larger library of compound mixtures many different compounds will have the same molecular mass. This greatly complicates structural determination and even makes it impossible at a certain mixture complexity. 

Some of the early examples of libraries yielding receptor agonists and antagonists were peptide-based. Houghten, Dooley and co-workers introduced synthetic peptide combinatorial libraries (SPCLs) in which defined mixtures of peptides were synthesized, cleaved from resin and assayed free in solution against either soluble (enzyme) or membrane associated (re-... 

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