Positional scanning deconvolution

A rather powerful deconvolution method reported is positional scan deconvolution developed by Houghten and co-workers [56] (Fig. 4). In this method a number of copies... 

The advantage of positional scanning over iterative deconvolution is that the sublibrary syntheses are carried out at once. But the number of split and pool operations that would be required for library synthesis is rather high so that building block mixtures are used in several of the library synthesis steps in order to reduce the number of operations. A thorough examination of the theoretical and experimental aspects of iterative and positional scanning deconvolution has been published [110],... 

A special type of combinatorial library is the positional scanning library (43, 49,58). This array contains a set of combinatorial libraries with one or more (two positions = dual positional scan (4, 59))deconvoluted positions. In each of the synthesized libraries the deconvoluted positions are different. After screening one can combine the positions of the spot with the peptides of highest activity of each library to obtain the complete sequence of a peptide with most likely the greatest activity. 

Although not identical, both the orthogonal and positional scan formatted libraries share the features that all mixtures are made at the start of the library process and only individual compound synthesis is required after the first screening of mixtures. This is an extra initial effort with regard to the synthesis of mixtures when compared to an iterative method. The advantage is that no intermediate mixture syntheses will be required. If prepared in sufficient quantity, the library can be screened over a large number of assays, and the added effort of initial mixture syntheses will be translated into an efficiency in deconvolution relative to the continual resynthesis of mixtures with iterative deconvolution. 

These techniques can be broadly split into two groups, the first of which can be represented by pooling methods, where deconvolution is obtained via various chemical steps, run in parallel or after the library synthesis. Pooling methods normally require multiple synthesis of many library members, including inactive individuals, in different pool formats. They are not single bead methods, so they are independent from analytical methods for structure determination. This group includes iterative deconvolution, recursive deconvolution, subtractive deconvolution, positional scanning and mutational... 

Iterative deconvolution Recursive deconvolution Subtractive deconvolution Positional scanning/indexing Mutational surf other methods... 

This is, together with positional scanning, the most popular deconvolution technique. It was introduced by Geysen et al. [9] and exploited by Houghten et al. [10] and Ecker et al. [11] for the deconvolution of peptide and oligonucleotide libraries, but it has been applied to the deconvolution of many small molecule libraries. 

Positional scanning, or 1-D indexing, was reported as a deconvolutive technique by Houghten and coworkers [35] and subsequently applied extensively to solid-phase peptide library synthesis. An example of solid-phase small organic molecule 2-D indexed library synthesis and deconvolution was reported by Berk et al. [36]. Description of this strategy, called spatially arrayed mixture (SpAM), and a comparison with classical positional scanning, are shown in Figure 8.9. 

Positional scanning was repeatedly used by Houghten and coworkers [38] in solid-phase peptide synthesis, but few examples of its application to small molecule libraries have been reported. Smith et al. [39] deconvoluted a solid-phase library of 1600 esters/amides, Andrus et al. [40] deconvoluted a solid-phase library of non-natural polyenes, Leone-Bay et al. [41] deconvoluted the activity of an indexed library in an in vivo assay, while Pirrung et al. reported both a solution phase 54-member carbamate library [42] and a solution-phase 72-member tetrahydroacridine library [43]. 

Initial selection procedure Iterative deconvolution Positional scanning Iterative deconvolution Positional scanning... 

Boger et al. [47] introduced the so-called deletion synthesis deconvolution as a process typical for convergent dimerization libraries, based on the methodical elimination of one element from the variable library units and on the evaluation of loss vs. gain of activity. This method was compared with positional scanning in a following paper by the same group [48] and proved to be effective and useful. 

Positional scanning was also examined, where the first sublibrary included only three subsets (XXP, XXR, and XXQ) due to the library construction and the other two included nine subsets (XNX, and XXN respectively, with N = determined monomer). GGR was the result of the deconvolution, and the increased reliability compared to the theoretical experiment [123] was attributed to the simplicity of this real library, while for more complex situations iterative deconvolution should still perform better than positional scanning. 

Peptides and Peptidomimetics from Combinatorial Libraries. Mixture-based combinatorial peptide libraries have been extensively explored by Houghten and coworkers and have led to the identification of a variety of peptides with affinity for opioid receptors (see Ref 946 for a review). Early hexapeptide libraries, deconvoluted by binding to p opioid receptors and either iterative deconvolution (947)or positional scanning (948 see Ref 946 for a description of these deconvolution techniques), identified sequences related to the enkephalins. Other nonacetylated peptide libraries have identified more varied peptides, some that resemble opioid peptides and some that do not. Iterative deconvolution of a hexapeptide library resulted in identification of both Tyr-Pro-Phe-Gly-Phe-XNH, (X = one of 20 natural amino acids), reminiscent of the... 

Figure 3 The deconvolution protocol known as positional scanning combinatorial.

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