Helical general synthesis

Protein helices generally adopt variations of the usual helix geometries depending on the environment. 1 The methods described in Sections 12.3.1 and 12.3.2 will refer only to the synthesis of peptides incorporating inducers and mimetics for the a- and 310-helices. 

The cyclooctapyrroles shown in Figure 55 appear predestined to form binuclear metal complexes since the loop-shaped conformation of these macrocycles exhibits two structurally identical, helical N4 cavities. Enantiomers of such complexes, which are presumably generally very stable towards racemization owing to the rigidity of the molecule imposed by the incorporation of the metal, are of interest as possible models for binuclear metalloenzymes and as potential catalysts in asymmetric synthesis. The first two ligands as well as their recently obtained palladium complexes601 were... 

Besides having a much lower molar mass than DNA, RNA generally forms only single-strand helices. RNA is often found associated with proteins inside cells. The most prevalent bases in RNA are the same as those in DNA, except that uracil is present instead of thymine. Three common types of RNA are ribosomal (rRNA), transfer (tRNA), and messenger RNA (mRNA). They are all involved in protein synthesis, controlling the sequence of amino acids that make up the primary structure. Thus the base sequence in RNA is related to the amino acid sequence in the protein that is made from it. 

In another study,a chiral templating procedure was employed to direct the helicity of an oligo-bipyridine, double-stranded copper(I) helicate. The strategy employed is illustrated in Figure 6.29 in which spiro-bisindanol 71 and dimethyl-biphenic acid 72 were employed as the chiral template starters for the twisting process inherent in helicate formation. The above approach serves as a model for a general route towards the synthesis of enantio-pure helicates and is also of considerable intrinsic interest since it illustrates the manner by which stereochemical information may be transmitted over nanometer distances. 

The helical axis is in general a line, but a recent development is the synthesis of circular helicates in which the ligands twist about a circle, the metal ions being disposed at regular intervals, and these are discussed in section 4.2. Reviews of helicates have appeared recently, and the reader is referred to these [23-25] for a discussion of properties of these complexes. 

Jackson DY, King DS, Chmielewski J et al (1991) General-approach to the synthesis of short a-helical peptides. J Am Chem Soc 113 9391-9392... 

Fig. 21-8 Replication of DNA double helix, (a) DNA synthesis at a pair of replication forks with expansion of the replication bubble. DNA chains are not shown in helical form, (ft) Complementary chains are synthesized via base pairing. (After J. McMurry and M. E. Castellion, Fundamentals of General, Organic, and Biological Chemistry, Prentice-Hall, Englewood Cliffs, NJ, 1992.) (c) Semiconservative replication. (After J. D. DeLeo, Fundamentals of Chemistry General, Organic, and Biological, Scott, Foresman, Glenview, IL, 1988.)...

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