Polyamide dendrons

Fig. 35 Reactions of the convergent synthesis of polyamide dendrons and dendrimers...

Figure 15.4. Polyamide dendrons prepared by Alper and coworkers on polystyrene support.

Scheme 15.7. Synthesis of 3,5-diamlnobenzoic acld-derived polyamide dendrons on solid support.

Figure 15.5. Supported polyamide dendrons derived from 4-azalysine.

The DAP polyamide dendrons conjugated to PNA-peptide chimera and decorated with Gd(III) complexes of D03A ligand were tested as plausible candidates for genetic molecular imaging using MR modality (Scheme 15.32). The Tj relaxivity was increased with the dendron generation. 

The utility and versatility of other polyamide dendron-modilied high-loading supports were demonstrated by Chan and coworkers in SPOS of sulfonamides, carboxamides, and other small molecules, as well as by Lee and coworkers in SPOS of pentapeptides. ... 

In the present context, solid-phase synthesis has been used primarily for the preparation of peptide and glycopeptide dendrimers [23]. For example, a second-generation dendrimer could be prepared by successive addition of branched polyproline building blocks to a solid phase [24]. The divergent synthesis of polyamide dendrimers on polystyrenes was accomplished [25] by Frechet el al. 1991 (cf. Fig. 2.8) [26]. PAMAM dendrons could be grown up to the fourth-... 

Newkome et al. prepared metallodendrimers with a ligand/metal/ligand architecture allowing separate construction of the dendrons. Two polyamide den-drons were preconstructed and linked to a ruthenium complex [38] (see Section 4.1.11). 

Denkewalter et al. [90] reported the synthesis of monodendron polyamides through generation 10. The scheme involved protection/deprotection methods commonly used by polypeptide chemists. Dendron construction started with benzhydrylamine as the initiator core and an activated ester of amino-protected L-lysine as the branching reagent (Scheme 4). 

Ishida et al. investigated the polycondensation of different monomers to aromatic polyamides with respect to the DB, namely 3,5-diaminobenzoic acid (AB2-monomer, DB = 32%), a G1 dendron (AB4-monomer, DB = 72%), and a G2 dendron (ABg-monomer, DB = 84%). The molecular weights of the resulting polymers were in the range of 100000- 200000 with a polydispersity of 3. ... 

Y. Ishida, A. C. F. Sun, M. Jikei and M. Kakimoto, Synthesis of hyperbranched aromatic polyamides starting from dendrons as monomers Effect of monomer multiplicity on the degree of branching , Macromolecules, 2000, 33, 2832-8. 

Jung and coworkers [84] described synthesis of biodegradable polymers consisting of the polyamide based dendrons and PNBE backbone (Figure 7.9). They reported ROMP of the first- and second-generation Newkome-style dendronized... 

Figure 7.9 Second-generation dendronized polymers consisting of the polyamide-based dendrons and PNBE backbone.

A different approach to dendritic sensors involves modification of a sensor core unit with dendritic substituents to confer beneficial solubility properties. An example of a sensor core unit is the porphyrin macrocycle, a heterocycle that has been employed extensively in prototypical photochemical sensor systems. Vinogradov and co-workers have exploited the versatile photoactive porphyrin sensor unit as a fluorescence-based pH indicator for use in biological assays [73], by attaching acid terminated polyamide-ether dendrons as substituents (Figure 8.12). The two imino nitrogen atoms present in the free-base porphyrin are susceptible to stepwise protonation to afford initially a cation and then a dication, respectively. Upon protonation, both the emission and absorption fluorescence spectroscopic characteristics of the porphyrin core are subject to dramatic hypochromic shifts. This spectroscopic phenomenon formed the basis for an accurate pH indicator with potential applications in proton gradient determination studies in biological systems. 

Many dendrons immobilized on insoluble support are, in fact, peptides or related polyamide structures. A number of reviews extensively surveyed peptide dendrimers, both soluble and support bound. ... 

The DAP, which was used by Reymond et al. in the synthesis of peptide dendrimers (see above), was adopted by Wickstrom and coworkers as a single building block for assembly of polyamide peptide-like dendrons on a PNA-peptide chimera presynthesized on a TentaGel Sieber resin (Scheme 15.9). Aminoethoxyethoxyacetate spacers were used to separate the various parts of this hybrid structure (peptide, PNA, and dendron) and HATU couphng... 

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