Side-chain functionalized

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... 

FIGURE4.il Reactions of amino acid side-chain functional groups. 

Sheremetev and co-workers employed diazo compounds of type 60, prepared from the corresponding amines in moderate yields as alternative excellent precursors for the preparation of side-chain-functionalized derivatives (Scheme 29). Several furazans bearing reactive groups or cyclopropyl or five-membered heterocyclic substituents have been prepared by standard procedures (99MI6). 

Side-chain functionalities react in an expected manner. For example, treatment of hydroxymethylfuroxan with HNO3 and H2SO4 gives the corresponding nitro ester (96IZV1782, 96RCB1692). 

Since most aaAAs are hydrophobic in nature, peptides rich in aaAAs are generally restricted to study in organic solvents due to their low solubility in aqueous media. There have been very few examples of side-chain functionalized aaAAs that would allow for the synthesis of highly water-soluble peptides rich in aaAA content.3 This is primarily due to difficulty of synthesis, since side-chain functionalized derivatives must be orthogonally protected to allow for incorporation into solid-phase peptide synthesis. The harsh conditions, under which standard methods of aaAA synthesis are performed, make this a difficult task. 

In the Boc protection approach, benzyl groups are used to protect the reactive amino acid side-chain functionalities because they are more acid-stable than the Boc groups. Trifluoroacetic acid (TFA) is sufficient to remove the Boc groups while leaving the benzyl groups intact (Fig. 3). 

An effect similar to that of cetyltrimethylammonium bromide micelles can be realized through the use of microgels with trimethylamino side-chain function and this may then allow solid supported microgels to be used in a continuous reaction. Evans et al. (1995) have utilized microgels incorporating 2-tetradecyl dimethyl amino/ethyl methacrylate bromide, which solubilizes aryl laurate esters in an aquous solution and catalyses the alkaline hydrolysis. 

Figure 1.6 The ionizable amino acids possess some of the most important side-chain functional groups for bioconjugate applications. The C- and N-terminal of each polypeptide chain also is included in this group.

Maehashi et al. (2007) used pyrene adsorption to make carbon nanotubes labeled with DNA aptamers and incorporated them into a field effect transistor constructed to produce a label-free biosensor. The biosensor could measure the concentration of IgE in samples down to 250 pM, as the antibody molecules bound to the aptamers on the nanotubes. Felekis and Tagmatarchis (2005) used a positively charged pyrene compound to prepare water-soluble SWNTs and then electrostatically adsorb porphyrin rings to study electron transfer interactions. Pyrene derivatives also have been used successfully to add a chromophore to carbon nanotubes using covalent coupling to an oxidized SWNT (Alvaro et al., 2004). In this case, the pyrene ring structure was not used to adsorb directly to the nanotube surface, but a side-chain functional group was used to link it covalently to modified SWNTs. 

A very large number of furoxan derivatives have been synthesised, taking advantage of the reactivity of side-chain functional groups in the ring [6, 9,11]. Here, the principal procedures used to synthesise the furoxan system will only be discussed briefly [6-8, 10] (Scheme 6.3). 

In this review, advances in the preparation of functionalized polysilanes by both pre- and post-polymerization functionalization and their properties will be reviewed. First, polymers with remote side-chain functionalities are covered, then those with the functionality directly attached to the main chain and finally those which are end group-functionalized. Chiral functionalization will be treated separately (see Section 3.11.6). 

The allyl protecting group has also been demonstrated to be useful for blocking of side-chain functionalities (36). Thus, the palladium(0)-catalyzed... 

SIDE-CHAIN FUNCTIONALIZED OR DENDRONIZED COPOLYMER HYBRIDS... 

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