Dendron construction

Figure 1.13 Overview of synthetic strategies for (a) branch cell construction, (b) dendron construction and (c) dendrimer construction annotated with discovery scientists...

More recently an interesting dendron construction method was reported independently by Frechet et al. [102] as well as by Neenan and Miller [103] which has been referred to as the 1(B) Convergent Method. This method differs from the divergent dendron approach in that exponential proliferation of surface groups is accomplished by use of a limited number of growth reactions per sequence. Its advantages and limitation will be discussed later. With this method a variety of dendron families have been successfully synthesized and subsequently coupled to various point-like as well as hyper-branched cores, to produce dendrimers. This... 

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). 

Ethers are chemically and coordinatively more inert than amides. Indeed, Frechet-type polyether dendrimers prepared in solution demonstrate a broad spectrum of chemical and coordinative compatibilities. Accordingly, polyether dendron synthesis on solid support was developed, initially by Bradley and coworkers and later by Portnoy and Dahan Instead of the 3,5-dihydroxy benzyl alcohol derivatives used in the soluble Frechet-type dendrimers, a more SPOS suitable 3,5-bis(hydroxymethyl)phenol unit was conceived as a building block for the dendron construction. 

Scheme 15.32. Synthesis of peptide-PNA-DAP dendron constructs gadolinium complexes.

Fullerene derivative 34 substituted with two long alkyl chains (solubilizing groups) and a carboxylic function was used as peripheral subunit for the constructions of the dendrons (Fig. 14). 

In their efforts to construct stimuli-responsive, supramolecular amphiphiles, Frechet et al. [126-129] reported the synthesis of a novel series of AB and ABA block copolymers via the Williamson ether synthesis (e.g., 47, Fig. 21). Polyethylene glycols (PEGs) of different lengths were used as the linear hydrophilic B block while polyaryl ether dendrons of different sizes were used as the hydro-phobic A block. These copolymers were characterized by optical microscopy,... 

Fig. 53. Mannosylated dendron based on a poly-L-lysine scaffold. This construct leads to subnanomolar inhibitory potency against uropathogenic E. coli,336...

The chemical composition of particles can be just as varied as their shape. Commercial particles can consist of polymers or copolymers, inorganic constructs, metals and semiconductors, superparamagnetic composites, biodegradable constructs, and synthetic dendrimers and dendrons. Often, both the composition of a particle and its shape govern its suitability for a particular purpose. For instance, composite particles containing superparamagnetic iron oxide typically are used for small-scale affinity separations, especially for cell separations followed by flow cytometry analysis or fluorescence-activated cell sorting (FACS). Core-shell semiconductor particles, by... 

The desired long spacer necessary to allow multiple branch construction, was obtained with commercial tetra(ethylene glycol) which was readily modified into aminoacetal 21 in five steps (Scheme 8). Using 21 as an amine source, poly(amidoamine) (PAMAM) dendrons were prepared according to published protocol using reiterative cycles of methyl acrylate and ethylenediamine reactions. The terminal amines of each generation (G = 1, G = 2 and G = 3, 22a-c) were obtained quantitatively from each of the half generation methyl ester precursors. 

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