Sequential-type synthesis

Linear polystyrene can be functionalized by various methods . The functional group capacity in these polymers diould not be too high otherwise, steric complications may arise. Poly(ethylene ycol) has been found to be most suitable for liquid-phase synthesis. This linear polyether and the block copolymers with functional groups at defined distances are chemically stable and soluble in a large number of solvents including water and can be precipitated selectively. Partially hydrolyzed poly(vinylpyrrolidone) and its copolymers with vinyl acetate were successfully applied in peptide synthesis. Poly(acrylic acid), poly(vinyl alcdiol), and poly-(ethylenimine) are less suitable for the sequential type synthesis because of the... 

Repetitive Sequential-Type Synthesis 2.3.1 Peptide Synthesis... 

The above drawbacks are to a greater extent overcome when using linear polyethers as soluble supports for the sequential type synthesis. The presence of a hydrophilic and hydrophobic moiety per monomer unit lends this class of polymers... 

The repetitive sequential-type synthesis on soluble polymeric supports has also been applied to the synthesis of oligonucleotides. As the coupling kinetics in liquid-phase... 

Peptides are not the only potential drug candidates. In most cases, other kinds of small organic molecules are preferred, because of their reduced susceptibility to enzymatic degradation. The split-mix method is fully applicable in the synthesis of organic libraries. Both sequential type and cyclic libraries can easily be prepared if the reaction conditions for solid phase are well developed. It has to be emphasized, however, that the advantages of the split-mix method can be fully exploited only in the case of multi-step synthetic procedures. For realization of the one-pot procedures suggested by Ugi [10], for example, the parallel procedures are better-suited. 

Like any other solid-phase methods of synthesis, oligonucleotide synthesis on polymer supports offers the advantages of ease and quickness of product isolation. Because the synthesis is a sequential type, the successive coupling operations can be done on intermediates still bound to the polymer. The method appears to be attractive for the synthesis of short... 

In supramolecular synthesis, on the other hand, different entities are held together via dynamic and reversible intermolecular interactions and, therefore, most synthetic procedures have to take place via a one-pot process. A supramolecular intermediate can rarely be prepared, isolated, and purified, and then added to another reactant in solution in order to perform sequential, assembly-line type synthesis, and herein lies a daunting challenge. How can we devise sophisticated and reliable synthetic routes for heteromeric supramolecular stmctures if we are limited to one-step reactions ... 

Scheme 42.40 Enantioselective sequential Hantzsch-type synthesis of dihydropyridine 177 starting from p-nitrocinnamaldehyde (175), anisidine (119), and ethyl acetoacetate...

The naphthoselenazole derivative (42 R = NHj) may be prepared by a Hantzsch-type synthesis from selenourea and 2-bromo-3,4-dihydronaphthalen-l(2 )-one-3-sulphonic acid followed by fusion of the product with sodium hydroxide. This amine (42 R = NHj) is ring-opened by sequential treatment with sodium borohydride and acetic anhydride to give compound (43), which may be cyclized to give the naphthoselenazole (42 R = Me). 

Whereas DNA has a single role as the storehouse of genetic information, RNA plays many roles in the operation of a cell. There are several different types of RNA, each having its own function. The principal job of RNA is to provide the information needed to synthesize proteins. Protein synthesis requires several steps, each assisted by RNA. One type of RNA copies the genetic information from DNA and carries this blueprint out of the nucleus and into the cytoplasm, where construction of the protein takes place. The protein is assembled on the surface of a ribosome, a cell component that contains a second type of RNA. The protein is consfructed by sequential addition of amino acids in the order specified by the DNA. The individual amino acids are carried to the growing protein chain by yet a third type of RNA. The details of protein synthesis are well understood, but the process is much too complex to be described in an introductoiy course in chemistry. 

The ion channel receptors are multi-subunit proteins which may be either homomeric (made up of multiple copies of a single type of subunit) or heteromeric (composed of more than one subunit type). These subunits come together after synthesis in the endoplasmic reticulum to form the mature receptor. Notice that stoichiometry is denoted by a subscript number. A receptor composed of two a and three /I subunits is therefore denoted as having a stoichiometry of This can cause confusion when related subunits are given sequential numbers /II, j]2, 3, etc. The convention is therefore that subunits are numbered normally while stoichiometry is indicated by subscripts so that a pentamer of a4 and j33 subunits might have a stoichiometry of a42/133. 

By combining several click reactions, click chemistry allows for the rapid synthesis of useful new compounds of high complexity and combinatorial libraries. The 2-type reaction of the azide ion with a variety of epoxides to give azido alcohols has been exploited extensively in click chemistry. First of all, azido alcohols can be converted into amino alcohols upon reduction.70 On the other hand, aliphatic azides are quite stable toward a number of other standard organic synthesis conditions (orthogonality), but readily undergo 1,3-dipolar cycloaddition with alkynes. An example of the sequential reactions of... 

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