Oligomer Syntheses

Monomer/Oligomer Synthesis. The first two steps in the four step reaction sequence of Figure 1 are capable of producing both monomer and oligomer. The first step, aromatic nucleophilic substitution, is a polymer forming reaction under the correct stoichiometric conditions. In order to favor the formation of monomer with a small amount of oligomer, the substitution was carried out at a 4 1 ratio of diol to dichlorodiphenyl sulfone. This led to a predominantly monomeric product (IV) with only the requirement that the excess diol be removed from the product to eliminate the potential presence of low molecular weight species in later reactions. 

Fig. 10.2 Trypsin mediated cleavage of a peptide bond in PNA oligomer synthesis...

Tietze LP, Kettschau G and Heitmann K (1996) Synthesis of N-protected 2-hydrox-ymethylpyrroles and transformation into acyclic oligomers. Synthesis 851-857. 

Template oligomer synthesis was described by Bohmer and Kammerer. Using p-cresyl-formaldehyde oligomers as a frame of the template, esters of aminoacids were prepared. The reaction, which may be considered as a model of a template reaction, was studied in its simplest form, based on the synthesis of cyclic dimers. The process can be represented by the following set of reactions (R - carbobenzoxy group) ... 

Efficiency of the deprotection and coupling reactions are critical to the success of any iterative solid-phase synthesis. Shown in Scheme 1 is a triad of reactions for phenylacetylene oligomer synthesis trimethylsilyl deprotection,28 29 triazene unmasking of an iodobenzene,30 and the Sonogashira coupling of a terminal acetylene with an aryl iodide.31-33 Representative procedures for each step in this sequence are included at the end of this chapter. 

A comparative study of phenylacetylene oligomer synthesis on a solid support14 with solution-phase approaches has been undertaken.37 Results from syntheses featuring a free and bound terminal acetylene are shown in Scheme 5. (For clarity, substituted arene units are symbolized as a filled circle throughout the rest of this chapter.)... 

The mechanisms of nucleotide oligomer synthesis catalyzed by proteinoids have not reported. A tentative mechanism rests on the supposition that the proteinoid nucleotide complex is an intermediate of an enzyme-like nucleotidyl transfer reaction. 

Figure 5 Most frequently used 2 -OH protecting groups in RNA-oligomer synthesis. DMF = N,N-dimethylformamide, PC = protecting group.

Despite the development of the exquisite methods for a-(2-8)-linked disialic acid synthesis discussed above, the assembly of the a-(2-8)-linked oligomer has been far from a success. Recently, Tanaka disclosed the unpredictable difficulty of the oligomer synthesis. As mentioned above, the coupling of A-Troc-protected sialic acid donor and acceptor successfully delivered the dimer of sialic acid. However, the A-Troc donor 163 was hardly incorporated into the A-Troc disialyl acceptor 164 the glycosylation produced the stereo mixture of trisial-ic acid 165 in 6% yield (O Scheme 45) [114]. 

The detritylation of support bound oligonucleotides during DNA synthesis has been studied. The efficiency of oligomer synthesis on a large scale can be enhanced by the use of more concentrated dichloroacetic acid solutions. ... 

Yamamoto and Suzuki coupling, and other common reactions in fluorene oligomer synthesis are illustrated in Fig. 3. 

Acridinium-NHS (AT-hydroxysuccinimide) ester labeling reagent is synthesized as described by Weeks et al. (1983) and probes containing an allylamine linker arm (Fig. 7.2.1) are prepared either as described for nucleotides and for enzymatically labeled probes (Section 7.6.2.2), by transamination (Section 7.8.1) or during oligomer synthesis (Section 6.4). The acridinium-NHS ester is then reacted with the linker arm by standard methods (Section 7.4.1). 

Transient siloxanolate anionic catalysts prepared by reacting four moles of D-4 with one of tetramethyl ammonium hydroxide at 80 C are effective for equilibrating "neutral" systems such as the epoxy ( ), "basic" dimethyl-amino (64) or aminopropyl (59,67) end-blockers and D-4. With "acidic" functionality on the end-blocker, we have successfully utilized trifluoroacetic acid for the equilibrations. Further details of the oligomer synthesis and their utilization in segmented copol)nners will be described in future publications. 

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