Oligonucleotide synthesis, combinatorial

This review has only lightly touched upon the topic of support stability under various reaction conditions. The main reason for this is that very little has been written on the subject. Many of those developing new supports have primarily done so for the fields of solid-phase peptide and/or oligonucleotide synthesis, areas which encompass a very narrow range of reaction conditions. As the field of combinatorial chemistry matures and new reaction types are attempted, an overall stability profile will gradually emerge. 

Nucleoside chemistry is traditionally labor intensive and the output of compoxmds is consequently relatively low. In order to overcome these limitations, several groups have implemented a parallel or combinatorial approach to speed up the synthesis process this chapter will only discuss the use of solid support for the synthesis of nucleoside libraries, not for the piupose of oligonucleotide synthesis. Chang <05BMC4760> attached a purine diehloride to a Merrifield 3,4-dihydropyran resin, followed by sequential displacement of the two ehloro atoms by various amines. The purine heterocyclic bases were then condensed with Dd.-ribofuranosides following a classical Vorbruggen method to yield nucleosides of general formula 171. 

Combinatorial Hbraries are limited by the number of sequences that can be synthesized. For example, a Hbrary consisting of one molecule each of a 60-nucleotide sequence randomized at each position, would have a mass of >10 g, weU beyond the capacity for synthesis and manipulation. Thus, even if nucleotide addition is random at all the steps during synthesis of the oligonucleotide only a minority of the sequences can be present in the output from a laboratory-scale chemical DNA synthesis reaction. In analyzing these random but incomplete Hbraries, the protocol is efficient enough to allow selection of aptamers of lowest dissociation constants (K ) from the mixture after a small number of repetitive selection and amplification cycles. Once a smaller population of oligonucleotides is amplified, the aptamer sequences can be used as the basis for constmcting a less complex Hbrary for further selection. 

Over the past decade the techniques of combinatorial synthesis have received much attention. Solid phase synthesis of polypeptides and oligonucleotides are especially adaptable to combinatorial synthesis, but the method is not limited to these fields. The goal of combinatorial synthesis is to prepare a large number of related... 

Figure 6.11 The use of oligonucleotides to encode a peptide combinatorial synthesis for a library based on two building blocks...

Automated synthesis of peptide and oligonucleotide libraries was initiated about 10 years ago [4], Within the last three years, there has been much attention focused on the generation of combinatorial libraries of small molecules. As with biopolymers, the use of solid resin support was central to the advance of this field. In solid-phase synthesis, one of the reactants is covalently bound to the solid support and an excess of the other reactants may be used in each step to drive reactions to completion. Purification of the intermediates and final product is easily achieved through extensive washing of the resin after each chemical step. For the purpose of high throughput synthesis, cleavage of the final... 

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