Undesired Reactions during Synthesis

Contents Introduction. - Structure Determination Amino Acid Analysis. Sequence Determination. Secondary and Tertiary Stmcture. - Peptide Synthesis Formation of the Peptide Bond. Protection of Functional Groups. Undesired Reactions during Synthesis. Racemization. Design of Schemes for Peptide Synthesis. Solid Phase Peptide Synthesis. - Methods of Facilitation. Analysis and Characterization of Synthetic Peptides. -Subject Index. 

Undesired Reactions During Synthesis benzyloxycarbonyl group ... 

Undesired Reactions During Synthesis of which here only the carboline derivatives... 

This reaction can be used for the synthesis of hydrocarbons but it may also take place as a side-reaction during generation of a Grignard reagent from an alkyl halide and magnesium, then leading to formation of undesired side-products. 

The dibromide itself is usually prepared from the same alkene and so the reaction is not particularly useful for the synthesis of alkenes. It is useful, however, in protection strategy. During a lengthy synthesis, it may be necessary to protect a double bond so that it does not undergo any undesired reactions. Bromine can be added to form the dibromide and removed later by denomination in order to restore the functional group. 

The whole-cell biocatalysis approach is typically used when a specific biotransformation requires multiple enzymes or when it is difficult to isolate the enzyme. A whole-cell system has an advantage over isolated enzymes in that it is not necessary to recycle the cofactors (nonprotein components involved in enzyme catalysis). In addition, it can carry out selective synthesis using cheap and abundant raw materials such as cornstarches. However, whole-cell systems require expensive equipment and tedious work-up because of large volumes, and have low productivity. More importantly, uncontrolled metabolic processes may result in undesirable side reactions during cell growth. The accumulation of these undesirable products as well as desirable products may be toxic to the cell, and these products can be difficult to separate from the rest of the cell culture. Another drawback to whole-cell systems is that the cell membrane may act as a mass transport barrier between the substrates and the enzymes. 

The essential part of SPPS is the protection of amino acid functional groups, which should not participate in peptide bond formation. To prevent undesired reactions with those functionalities, the so-called protection groups are required. There are two types of protection groups used in SPPS. The first protects the functional groups of amino acid side chains and should remain stable during the peptide synthesis process but be easily removed after the synthesis is complete. The second is a protection group of the alpha amino group in amino acids. This... 

Undesired reactions may also be caused from the choice of monomers and special attention needs to be taken to avoid these. As stated in the synthesis section, side reactions may occur from certain functionalities and byproducts. Thus, amino- and especially mercapto-functionalities may add to the vinyl groups in general and acryl groups in particular before and during polymerization, and unless these features are controlled, it is safer to use monomers devoid of reactive amines and thiols. Amino groups may also be made less reactive by alkylation. 

Elimination of trifluoromethane was undesirable reaction which was observed during attempted stereoselective synthesis of HIV 1 reverse transcriptase inhibitors via intermediate 1154 it occurred upon treatment of 1154 with bases (Scheme 261) [702]. 

Promotion We use the term promotion, or classical promotion, to denote the action of one or more substances, the promoter or promoters, which when added in relatively small quantities to a catalyst, improves the activity, selectivity or useful lifetime of the catalyst. In general a promoter may either augment a desired reaction or suppress an undesired one. For example, K or K2O is a promoter of Fe for the synthesis of ammonia. A promoter is not, in general, consumed during a catalytic reaction. If it does get consumed, however, as is often the case in electrochemical promotion utilizing O2 conducting solid electrolytes, then we will refer to this substance as a sacrificial promoter. 

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