Cleaved from Individual Beads

A second paradigm for deconvolution is through libraries based on an encoded bead method (Fig. 6). In this method a readable chemical tag was simultaneously attached to the individual bead for each step in the synthesis of the actual molecule on the bead [66], Herein the library is based on a one-bead-one-compound method, and the activity is measured for individual beads. This determination of activity can be while the test compound is still attached to the bead, where the tag is read directly after the activity is measured. Alternatively, the test compound is cleaved from the bead in a manner that, once activity is detected, allows one to directly return to the individual bead in order to read the tag. The original research in this area was done by Lam and co-workers [14,67, 68], These efforts have progressed to the issuance of a U.S. patent on the one-bead-one-compound methodology with claims for peptide libraries [69], The consequences of the appearance of this patent to those using one-bead-one-compound methods are undetermined at this time. 

There are two approaches to analytical evaluation of OBOC libraries analysis of compounds from individuals bead [51,60] and analysis of mixtures of compounds detached from multiple beads [61, 62], It should be mentioned that analysis of mixtures from OBOC libraries is quite different from that described in section Analysis of Libraries Synthesized in the Format of Small Mixtures of 4-12 Compounds per Mixture. In the mixture of compounds cleaved from a few beads, which are randomly picked for analysis from the OBOC library, the structures of components of the mixture are unknown. Consequently, it is not possible to apply the strategy developed for the analysis of mixtures synthesized in spatially addressed format, which is based on information about the structures of components of each mixture. In the case of OBOC libraries, analysis of only very large mixtures is meaningful when the theoretical distribution of molecular weights within the whole library is compared with that experimentally observed [61, 62], The focus of this section is on characterization of OBOC libraries through analysis of individual beads. 

In 1985, Houghten [11] used this method in his tea bag approach described in section 3.4.4.2 of this chapter. As an elemental synthesis unit, instead of individual resin beads, he used small batches of resin packed into a polypropylene mesh. Furka [12,13] described the split/pool methodology for the synthesis of peptides. The peptides were cleaved and analyzed as mixtures and separated by HPLC as a rapid method for multiple peptide synthesis. In his work, Furka did not suggest explicitly to cleave individual compounds from individual beads. This seemingly obvious idea was recognized by Lam [14,15]. Split/pool synthesis was further developed and widely used by many others working in-the field of combinatorial chemistry [16]. The new Journal of Combinatorial Chemistry published a very interesting historical perspective on the major events in this field [17],... 

Libraries prepared by application of real combinatorial synthetic methods are usually submitted to screening experiments, either as soluble mixtures or as unknown discrete compounds cleaved from, or tethered to individual beads of the solid support. The task in deconvolution is to identify the substance that has a desired property. The deconvolution methods can be classified into two groups deconvolution of mixtures, cleaved from support and deconvolution of tethered libraries. 

As each resin bead contains only a single molecule the beads can be screened individually for bioactivity by either screening for activity of bound peptide in the biological assay or by cleaving the resultant peptide from the bead before undertaking the bioanalysis. The identity of any active compounds can then be determined by using mass spectrometry to sequence the active peptide. 

Cleaving the product from a single bead and test it as an individual... 

Peptides synthesised as individuals or mixtures on solid supports such as resin beads derived from polystyrene, polyacrylamide, polyacrylamide/polystyrene co-polymers (cf. Chapter 15) and cleaved to be assayed in solution. 

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