Parallel peptide synthesis

Palmitic acid, structure of, 1062 Palmitoleic acid, structure of, 1062 PAM resin, solid-phase peptide synthesis and, 1037 Para (m), 519 Paraffin, 91 Parallel synthesis, 586 Parent peak (mass spectrum), 410 Partial charge, 36 Pasteur, Louis, 297, 307... 

Modern combinatorial chemistry involves a number of steps that begin with the creation of a library of molecules that are closely related in structure. The library can be created in two ways (a) parallel synthesis, which is simultaneous synthesis of numerous products in separate discrete reaction vessels (b) combinatorial synthesis, of numerous reactions within one single reaction vessel followed by separations. The initial successes in parallel synthesis have been in solid peptide synthesis of proteins, which was based on Merrifield s solid-phase peptide synthesis. 

In a parallel study, Wipf and Fritch11041 have shown that also urethane-protected (Boc), and even amino acid segments, are tolerated as acyl compounds on the aziridine nitrogen. The best results were obtained with alkylcopper reagents derived from CuCN and an alkyl-lithium in the presence of boron trifluoride-diethyl ether complex. Some 6-alkylated compounds (11-15%) were isolated as well. This work was extended to a solid-phase procedure that resulted in resin-bound alkene isosteres that could immediately be used in further peptide synthesis.11051 For this purpose, the 2-nitrophenylsulfonyl (oNbs) group was used for nitrogen protection and aziridine activation. It could be readily cleaved with benzenethio-late, which was compatible with the acid-sensitive Wang linker used. 

Future developments in peptide synthesis research will aim at clarifying the mechanisms of initiation, A-methylation, elongation, epimerization, and termination events on peptide synthetases. Parallel work will concentrate on the elucida-... 

At each stage in the peptide synthesis a second parallel synthesis is carried out on the same bead to attach the oligonucleotide tag (Figure 6.11). In other words, two alternating parallel syntheses are carried out at the same time. On completion of the peptide synthesis, the oligonucleotide tag is isolated from the bead and its base sequence determined and decoded to give the sequence of amino acid residues in the peptide. 

Solid phase methods have been adapted so that many different peptides can be synthesised in parallel on filter paper (Frank 1989). For example, by using a 10 x 10 grid, 100 different peptides can be synthesised simultaneously by incorporating different amino acid at different positions on the filter. This is a simple way of preparing many different peptides very economically for applications such as epitope mapping. Equipment also exists for carrying out automated peptide synthesis in parallel. 

Besides performing multiple syntheses in parallel, the accelerating of reaction rates may also achieve the same result— production of multiple peptides in the same time period. CEM (http //www.cem.com) has employed microwave irradiation to shorten both coupling and deprotection times. Their synthesizer, Odyssey (Fig. 7), achieves one cycle of peptide synthesis (Fmoc-based) in less than 10 min and is theoretically capable of the synthesis of 12 peptides in a row. However, for each new peptide the reaction vessel has to be cleaned and new batch of resin has to be transferred into it. This step raises concerns with the authors of this review about the possibility of cross-contamination. 

Kuroda, N., Hattori, T., Fujioka, Y., Cork, D. G., Kitada, C., and Sugawara, T. (2001) Application of automated synthesis suite to parallel solution-phase peptide synthesis. Chem. Pharm. Bull. Tokyo 49, 1147-1154. 

Most synthetic methods for the generation of peptide libraries have been derived from various multiple parallel peptide synthesis techniques developed since 1984.bs-i l Consequently, the sohd supports used for hbrary synthesis are essentially the same as those used for multiple peptide synthesis. Standard divinylbenzene cross-linked polystyrene resins are typically used for hbraries that are cleaved from the resin and screened in solution.P Polyoxyethylene-grafted polystyrene resins,f l or acrylamide-polyoxyethylene copolymers, P on the other hand, are the sohd supports of choice for the synthesis of resin-bound peptide hbraries screened in sohd-phase binding assays.P Such resins are compatible with both organic solvents used for peptide synthesis, as well as aqueous buffers used in the bioassays. Various segmental supports previously employed for multiple peptide syntheses have also been utilized for the synthesis of peptide libraries, including polypropylene pins, PI cotton,t cellulose membrane,and glass shdes.P ... 

A special case of parallel synthesis is the spatially addressable synthesis pioneered by Fodor et al. [17,18] in 1991. Here, each member of the library is synthesized at a specific location on a functionalized silica wafer rather than on resin beads in separate reaction vessels. This approach, based initially upon solid-phase peptide synthesis and semiconductor photolithographic techniques by using photolabile amino protecting groups, allows the synthesis of combinatorial libraries containing about 50000 compounds localized to a 50 pm square site on a silica wafer ( library on a chip ). 

In this section, we wish to discuss the results of recent studies on cyclopeptides carried out by our group [97-99]. Cyclopeptides as molecular receptors have been immobilized on different sensor surfaces, and can be prepared in high diversity by parallel solid-phase peptide synthesis (SPPS) [100], However, functional groups for the attachment to the surface must be available. On the other hand, the interaction with the analyte should be as specific as possible, and for this reason appropriate side chains must be selected. 

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