Wyniki wyszukiwania - BazTech

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Synteza chemiczna oligonukleotydów na fazie stałej. Możliwości i ograniczenia nośników stałych

Burzyńska-Pędziwiatr I., Woźniak L.

Wiadomości Chemiczne

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2008

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[Z] 62, 7-8

571-594

EN

Synthesis of biopolymers (peptides, proteins and nucleic acids) has long been in the range of interest of numerous chemists. The primary structure of biomolecules consists of linear and repeating sequences of monomeric units (aminoacids, nucleic bases, sugars) in a specifically determined orientation. Therefore, chemical synthesis of biopolymers comprises a lot of identical, repetitive steps (condensation, chain elongation and purification). Solid phase method is currently used also for the oligonucleotide [2, 3] (Figure 1) and oligosaccharide synthesis. There exist interesting applications of analogous approach to combinatorial synthesis of small molecules (Solid Phase Organic Chemistry - SPOC) [4, 5]. Automation of the phosphoramidite method of oligonucleotide synthesis process proposed by Caruthers [6] made an enormous impact on biological, medical and biotechnological sciences. It is beyond any doubt that this is the fastest and the most convenient method of oligonucleotide synthesis aimed at biological research. Solid phase synthesis has many advantages, however, it is not free of drawbacks either. Depending on the synthesis method, various types of supports are used. An ideal support should have an appropriate and reactive chemical group on its surface, e.g. -NH2, -OH, -COOH, by means of which it is connected to the linker and the first unit of the monomer. Surface functionalization of the solid phase determines the number of available reactive groups and characterizes support loading expressed in micromoles per gram. Nucleosides are attached to the support by a linker, the choice of which depends on the reaction conditions. The linker arm must be designed in such a way that it is adjusted to the cleavage conditions and deprotection procedures. Depending on the synthesis purpose and the type of a oligonucleotide, various linker arms are used. They include: linker arms cleaved after synthesis, labile linker arms, universal linkers [21, 22], and the linker arms for deprotection of the immobilized products [26, 27]. Among numerous methods of oligonucleotide synthesis, the phosphoramidite method is the most common. The phosphoramidite approach (Figure 10) allows for obtaining both natural DNA/RNA and plenty of modified analogs (phosphorothioates, phosphoroselenoathes, triesters and others). Its alternative is the H-phosphonate method (Figure 11) [40-42]. Particular advantage of this method is that it can be used in the synthesis without protection of nucleobases. Depending on its destination, the synthesis must be very carefully designed considering the strategy of group protection to make them stable under reaction conditions. A decision must be also made whether to use the phosphoramidite method or the H-phosphonate method taking also into account whether the product is to be immobilized on the support or not, which depends on expected results.

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Koniugaty peptyd-oligonukleotyd : synteza i zastosowanie

Kaczmarek R., Radzikowska E., Baraniak J.

Wiadomości Chemiczne

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2008

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[Z] 62, 11-12

1091-1113

EN

Recently major advances have been made in the development of oligonucleotides as potential therapeutic agents [1-3]. However, a frequent limitation of their use is poor cellular uptake [5]. Among the many molecules that have been reported to enhance cell delivery of oligonucleotides there is a number of peptide carriers. They are preferably linked by covalent bond in many possible ways, resulting in a new class of compounds known as peptide-oligonucleotide conjugates (POCs) [6a, 9]. A variety of chemical linkages have been used to link the peptide and oligonucleotide fragments. A peptide can be conjugated either at the base-, 3'-, or 5'-position of the sugar unit or at the backbone of the oligonucleotide [10]. Similarly, the point of conjugation in a peptide can be either the C- or N-terminus or the side chain. Two different strategies have been adopted for the synthesis of POCs: in-line solid-phase synthesis (divergent method) and fragment conjugation (convergent method) [11]. In divergent method, the peptide and oligonucleotide fragments are assembled on automatic synthesizers, sequentially on the same solid support, until the final step. In predominant cases, the peptides are assembled first by the Fmoc method, while the oligonucleotides are assembled next using the phosphoramidite method [12]. In-line synthesis could be most direct for preparing POCs, but finding the right combination of protecting groups is the key problem. The first step in preparation of POCs involves modification of solid supports with suitable linkers [10]. A number of monofunctionalized as well as bifunctionalized linkers were immobilized over solid supports through suitable spacers (Figure 1). In the fragment conjugation, the peptide and oligonucleotide fragments are synthesized individually, cleaved from their solid supports, deprotected and purified, separately. Therefore, the most appropriate synthetic chemistry can be used for each component without concern for incompatibility. Both biopolimers are finally linked postsynthetically utilizing the reactive functional groups which are attached at the desired site of conjugation (Figure 4) [5]. If the postsynthetic conjugation is performed with one of the oligomers still joined to the solid phase, it is called the solid-phase fragment conjugation method. Alternatively, if the conjugation is effected after complete isolation and purification of the peptides and oligonucleotides, it is called fragment conjugation in the liquid phase [10]. Besides their potential use for therapeutic applications, POCs can serve as research tools, for example, as fluorescent probes [44] or PCR primers [25, 45]. With increased specificity and strength of target binding, POCs may be useful in diagnostic applications or as affinity purification reagents.

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Narzędzia chemii kombinatorycznej. Cz.2. Łączniki stosowane w syntezie organicznej na fazie stałej

Łaźny R., Michalak M.

Wiadomości Chemiczne

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2003

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[Z] 57, 11-12

1061--1091

EN

Linkers constitute fundamental tools of polymer supported synthesis and combinatorial chemistry. Synthesis of any compound on solid support requires an efficient method for binding substrate molecules to solid phase and methods for cleavage of product molecules from the support after completion of the synthetic sequence. This review article presents role of linkers in solid-phase synthesis, analogy between linkers and protecting groups, and properties of linkers that need to be considered when planning synthesis of a particular compound on solid support. Basic concepts of linker methodology are presented and illustrated with selected examples. In addition the role of the linker as protection or activation of functional group of the substrate and an element controlling regio- or chemoselectivity is mentioned. The selected, representative examples of classical and recently elaborated linkers are classified according to the condition of cleavage. These include acid sensitive, base or nucleophile sensitive, photolabile, safety catch linkers, traceless linkers and cyclative cleavage linkers.