Protecting groups. Table

The next peptide bond must be made to the ringed nitrogen atom, so treatment with HBr frees this amine without affecting the other protecting groups (table T 9.1). 

Selective methods for deprotecting glycopeptides either at the amino or at the carboxyl terminus have been developed during the past decade by introduction and application of different combinations of protecting groups (Table II). 

Linkers are usually categorized according to the kind of functional group or substrate class they can selectively immobilize (linkers for carboxylic acids, alcohols, amines, etc.). Because a variety of types of linker is available for solid-phase synthesis, many belong to certain well-established classes of protecting group (Table 6.1.1) and can therefore be grouped into linker families. The members of each family have certain reactivity patterns in common. 

As discussed above, each linker family is sensitive toward a certain spectrum of cleavage conditions and is therefore stable to dissimilar conditions. Since most of the linkers are based on well-established protecting groups, table 6.1.2 can be used for the determination of orthogonality. For example, benzyl-type linkers, most of which are cleaved by electrophiles, and are stable towards nucleophiles, can be combined with ester-based protective groups. 

Table V, Entries 5 and 6). The catalyst tolerates both sulfur and nitrogen substituents (Table V, Entries 2, 4, and 8). Protected (1-ami no-alcohols are smoothly converted into the corresponding aldehydes without detectable racemisation (Table V, Entries 4 and 8) (28). It is also noteworthy that the reaction conditions are sufficiently mild as to be compatible with the Boc protecting group (Table V, Entry 8). 

The 6-mono-0-trityl cellulose or the more efficient 6-0-mono-0-(4-monomethyoxytrityl) derivative, and 6-mono-O-TDS cellulose were used to synthesize regioselectively functionalized cellulose ethers at positions 2 and 3 after the exclusive cleavage of the protecting groups (Table 16.10). In case of the trityl derivatives, the deprotection is carried out most efficiently with HCl in a suitable solvent. For TDS protected derivatives, tetrabutylammonium fluoride in THF is most successful for the cleavage of the silyl groups. 

Table 19. Protecting groups used for nucleotides (see also section 2.6.).

An important reaction parameter is the choice of the base and NajCO or NaOAc have been shown to be preferable to EtjN in some systems[2]. The inclusion of NH4CI has also been found to speed reaction[2]. An optimization of the cyclization of A -allyl-2-benzyloxy-6-bromo-4-nitroaniline which achieved a 96% yield found EtjN to be the preferred base[3]. The use of acetyl or inethanesulfonyl as N-protecting groups is sometimes advantageous (see Entries 4 and 5, Table 4.1). 

Several of the ammo acids listed m Table 27 1 bear side chain functional groups which must also be protected during peptide synthesis In most cases protecting groups are available that can be removed by hydrogenolysis... 

Several methoxy-substituted benzyl ethers have been prepared and used as protective groups. Their utility lies in the fact that they are more readily cleaved oxidatively than the unsubStituted benzyl ethers. The table below gives the relative rates of cleavage with dichlorodicyanoquinone (DDQ). ... 

An interesting observation was made in regard to the polymeriza-bility of N-acylhydroxyproline derivatives The monomers with the smallest protecting groups such as N-acetyl and N-pivaloylhydroxy-proline gave rise to the polymers with the lowest molecular weights (Table 1). When these monomers were polymerized, the initially... 

Developments of protection strategies in peptide synthesis have led to the introduction of a wider variety of protecting groups for different functionalities and provide orthogonal protection to specific side chains (Table 1). 

Peptide Synthesis and Self-Assembly Table 1 Common side-chain protecting groups... 

Table 3.1 gives the structure and common abbreviation of some of the most frequently used hydroxy-protecting groups. 

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