Unnatural biopolymer

Burgess, K. Linthicum, D. S. Shin, H. Solid-Phase Synthesis of Unnatural Biopolymers Containing Repeating Urea Units, Angew. Chem. Int. Ed. Engl. 1995, 34, 907. 

CY Cho, EJ Moran, SR Cherry, JC Stephaus, SPA Fodor, CL Adams, A Sundaram, JW Jacobs, PG Schultz. An unnatural biopolymer. Science 261 1303-1305, 1993. 

An alternative procedure for urea formation starts from pNP-OCOCl and two amines. Repeating urea units afford unnatural biopolymers. TentaGel is often used as resin. ... 

Opportunities for New Chemical Libraries Unnatural Biopolymers and Diversomers... 

A recent review (146) examines the features of several synthetic biopolymers mimicking the structures of both peptides and nucleotides and critically analyzes the future opportunities for each unnatural oligomeric family of compounds. 

Ayers, B., Blaschke, U. K., Camarero, J. A., Cotton, G. J., Holford, M., and Muir, T. W. (1999) Introduction of unnatural amino acids into proteins using expressed protein ligation. Biopolymers 51, 343-354. 

Life would have been impossible without the chirality of its molecules, which is required for the larger spectrum of biomolecules, their 3-dimensional assembly, and for the functions of biopolymers. In this balance, the unnatural, nonprotein amino acids detected in some meteorites may have played an especially significant role. 

For polymeric chains, the act of coordination almost invariably requires a change in the shape of the chain as a consequence of satisfying the demands of the metal ion for a preferred stereochemistry and a set of donors with bond distances within a limited range. Thus, coordinate bond formation has consequences that clearly alter the local environment around the metal ion, but may also alter polymer chain conformation over an extended range. Since three-dimensional shape in biopolymers plays a role in function, natural complexation evolved by Nature usually plays a positive role, whereas unnatural complexation through the addition of foreign metal ions may be deleterious to function. 

Instructed, reproducible self-assembly of this type can be seen in numerous disciplines. In polymer chemistry, certain oligo(phenylene ethylenes) undergo solvophobic folding into helical conformations in polar solvents. " In peptide science, synthetic polypeptides containing unnatural P-amino acids spontaneously adopt helical dispositions in solution, despite being unable to form the hydrogen bonds that drive self-assembly in normal biopolymers. 

It is well known that nature folds macromolecules like proteins, RNA, and DNA into defined stmctures with specific shape and that these shapes are intimately related to their function [14-18]. Tremendous research effort has provided some understanding of how this folding occurs in proteins. In fact, it is now possible to design, from scratch, with great success an unnatural protein sequence which will fold into the predicted secondary stracture [19]. However, many of the fundamental questions of biopolymer folding are not yet solved. Careful study of foldamers, which can be... 

The force fields used for biopolymers (and unnatural polymers) are typically simplified versions of the general force field described above. For example, proteins and nucleic acids rarely have C-C bonds that are substantially elongated from normal values or valence angles that are greatly expanded or contracted. Typically, biomolecules achieve their complexity by concatenation of fairly ordinary organic structures, not by distorting molecules from their usual structural parameters. This allows simplifications to be made. 

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