Secondary side, modification reactions

The primary polyphosphazene synthesis processes discussed above provide access to an enormous variety of different macromolecules. Yet further structural diversity can be achieved by carrying out modification reactions on the organophosphazene polymers produced in these primary rections. Secondary reactions are particularly important for the preparation of polymers with functional units in the side group structure, species that would be difficult or impossible to produce by the primary synthesis methods. 

Fig. 9. The transacetylase ribozyme. A Secondary structure of the clone 11 transacylase ribozyme based on the Zuker RNA folding algorithm Mfold. The oligonucleotide substrate is shaded in gray. The 2 -OH group of cytosine 147 (arrow) is the site of modification of the oligonucleotide substrate. B Reaction catalyzed by the clone 11 transacylase ribozyme. Note that the equilibrium of the reaction lies strongly on the side of the Bio-Phe-AMP substrate...

Oxidative amino acid side-chain modifications do not result in a stable end product of the oxidation process, but very often highly reactive intermediates are formed. These include chemically reactive groups, like ketones and aldehydes, or the formation of protein hydroperoxides. The presence of such protein hydroperoxides leads to a process called protein peroxidation. Here secondary reactions occur if the protein hydroperoxide decomposes and initiates further oxidative reactions, again forming oxidized protein forms. 

Solute transport across the cytoplasmic membrane of bacteria occurs by two major mechanisms (i) Secondary transport systems transport by these systems is driven by electrochemical gradients and will lead to the translocation of solute in unmodified form (ii) Group translocation solute is substrate for a specific enzyme system in the membrane the enzyme reaction results in a chemical modification of the solute and release of the products at the cytoplasmic side. The only well-established group translocation system is the phosphoenolpyruvate phospho-transferase system (PTS) (see below). 

Modification of the electrolyte composition affects dominant and secondary electrochemical processes during the charge and discharge phases, as well as the fundamental manner in which the various species in solution interact with each other within the battery s environment. Undesirable side-reactions may be major contributors to coulombic losses within the system, and could possibly be circumvented or reduced. Hence fundamental studies are needed to identify and propose measures to minimize such unwanted side-reactions between novel BSAs or other functional additives and other species present in the electrolyte. 

The use of secondary amides as nucleophiles has been also documented by Mori et al.f Synthesis of imides by this method is not always satisfactory, but phthalimides are prepared in high yield (Scheme 44). An interesting modification of this method consists of the double carbonylation of o-aryl diiodides and proceeds via an initial intermole-cular amidation, followed by the intramolecular one described by Mori (Scheme 45). ° The formation of seven-membered rings was demonstrated by the synthesis of diazepam and a number of anthramycin alkaloids, including Prothracarcin and Tomaymycin (Scheme 46). As mentioned above, for seven-membered rings direct amination is observed as a side reaction. Secondary ureas are also substrates for this reaction, yielding seven-membered cyclic ureas. ... 

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