Combinatorial spot synthesis

Besides classical resin beads, other polymeric carriers were also used for the synthesis ofpeptide libraries in various formats. Poly aery late-grafted polypropylene pins were used for the synthesis of the first combinatorial chemical library [1,2], This type of support continues to be heavily used in multiple peptide [27] and non-peptide [28] library synthesis. Cellulose paper, originally used by Frank et al. as a solid-phase support for oligodeoxy-ribonucleotide synthesis [29], has also been used as the support for multiple SPOT synthesis of peptide libraries [30,31], Polystyrene-grafted polyethylene film (PS-PE) may also be used in combinatorial peptide library synthesis [32], The specific feature of the membrane type of carrier is its dividability. This feature has been used for the synthesis of libraries with a nonstatistical distribution of library members, where no compound is missing and none is represented more than once [33],... 

A different way to produce chemical microarrays in situ is spot synthesis of combinatorial libraries on cellulose sheets [56]. Spot synthesis is configured as an open system to be operated at room temperature. Despite attempts to replace cellulose with polypropylene as a synthesis support [57], cellulose is still the support of choice for spot synthesis, and reaction conditions have to be compatible with the restricted chemical stability of cellulose. Due to the acid labihty of such membranes, the diversity content of these arrays was initially restricted to the synthesis of peptides. Recently, a method was described that could widen the scope of spot synthesis arrays. Germeroth and coworkers [57] succeeded in the assembly of a library of 8000 cellulose-bound 1,3,5-triazines under mild reaction conditions. They employed a strategy that took advantage of a temperature-dependent, successive displacement of cyanuric chlorides by different nucleophiles in a first report of the synthesis of smaU organic compounds on ceUulose sheets. 

With the concept of combinatorial chemistry and the construction of chemical libraries the issue of the structural elucidaton of active leads emerged. If compounds are generated individually in a parallel synthesis, their structure is obviously predetermined. Similarly, compounds that are physically constrained to a location are accurately defined by their position. Resourceful strategies that have been employed include the spot-synthesis on paperthe multipin, Diversomer , i27 photolitographic, and the teabag technique. ... 

Since it is unlikely for one to be able to synthesize all possible sequences on a single spot, do not start synthesis of a combinatorial library with more than 6 mixture positions. If necessary, start to screen 8mer peptides (6 mixture + 2 deconvoluted positions) and extend the peptide length with each synthesis round by extending the deconvoluted positions and maintaining the number of mixed positions (e.g., 6 mixture + 4 deconvoluted positions). 

Blackwell, H.E. (2006) Hitting the SPOT small-molecule macroarrays advance combinatorial synthesis. Curr. Opin. Chem. Biol. 10, 203-212. 

Frank, R., Kiess, M., Lahmann, H., Behn, C., and Gausepohl, H. (1995) Combinatorial synthesis on membrane supports by the SPOT technique. In Peptides 1994 Proceedings of the 23rd European Peptide Symposium, ed. H.L.S. Maia, pp. 479-480. Leiden ESCOM. 

Adler, F., Turk, G., Frank, R., et al. (2000) A new array format for the automated parallel combinatorial synthesis by the SPOT-technique. In Innovation and Perspectives in Solid Phase Synthesis (Epton, R., ed.), Mayflower Worldwide, Kings-winford, UK, pp. 221-222. 

Combinatorial libraries are prepared by the (1) parallel synthesis of arrays, (2) split-pool method, (3) biological method, or (4) spatially addressable parallel synthesis [74,78-80]. Parallel synthesis is carried out by the simultaneous synthesis of an array of different compounds. Several methods are available. In the multipin method, the peptide synthesis is carried out on polyethylene rods that have attached protected amino acids [81]. The amino acid sequence of a synthesized peptide on a particular pin depends on the order in which the amino acids are added. The number of products synthesized is the same as the number of pins. Another version of parallel synthesis, known as the teabag method, uses resin-filled bags in place of pins [74]. By pooling the resin portions from the appropriate bags, followed by redistribution and further coupling with a specific amino acid, a peptide library can be synthesized. The SPOT method uses a cellulose paper membrane as a solid support, which acts as an open reactor. Respective reagent solutions are pipetted onto several spots to synthesize as many peptides as the spots chosen [74,82]. 

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