PAMAM dendrons

Huang, B., and Tomalia, D.A. (2005) Dendronization of gold and CdSe/cdS (core-shell) quantum dots with tomalia type, thiol core, functionalized poly(amidoamine) (PAMAM) dendrons. J. Lumin. Ill, 215-223. 

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. 

Scheme 8 Synthesis of PAMAM dendrons having aldehyde functionality at the focal point and sialylated dendrons using reductive amination...

Fig. 7.13 PS-PEG-PAMAM dendronized support with HMPB-linker.

Bradley described the first solid-phase synthesis of PAMAM dendrimers in 1997 [220]. To this end, phthaloyl-protected norspermidine was coupled to aminomethyl functionalised polystyrene-polyethylene-glycol resin ((PS-PEG)-NH2) through an acid-labile linker (see Fig. 23). PAMAM dendrons were assembled by treating deprotected scaffold-bound resin 24 first with an excess of methyl acrylate... 

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-... 

ACRONYM, TRADE NAMES PAMAM dendrons and dendrimers, Slarburst dendrons and dendrimers... 

Mizugaki T, et al. PAMAM dendron-stabiUsed palladium nanoparticles effect of generation and peripheral groups on particle size and hydrogenation activity. Chem Commun 2008 2 241-3. 

Aranishi K, Zhu QL, Xu Q. Dendrimer-encapsulated cobalt nanoparticles as high- performance catalysts for the hydrolysis of ammonia borane. Chem Cat Chem 2014 6 1375-9. Mizugaki T, et al. PAMAM dendron-stabilised palladium nanoparticles effect of generation and peripheral groups on particle size and hydrogenation activity. Chem Commun 2008 241-3. 

Additional examples of dendritic-type surfactants were reported in the early patent literature as hydrophobic core functionalized PAMAM dendrons [35,168]. For example, when the core was a 12 carbon chain, the first two generation PAMAM dendrons exhibited hydrocarbon solubility (TMF). 

Scheme 15.11. Synthesis of PAMAM dendrons on solid support.

In recent years, PAMAM on polystyrene was also synthesized by other groups. " A similar methodology was used by Wang and coworkers to assemble PAMAM dendrons on multilayer microspheres consisting of a magnetite core covered by an intermediate methyl methacrylate-divinylbenzene polymer shell and polyglycidyl methacrylate outer layer (Scheme 15.12)." ... 

PAMAM dendrons were also prepared on silica, as early as 1998, by Tsubokawa et al. and by many other groups, such as Arya and Alper, Kunitake, Rhee, Bu, Kawi, Qiu, Imae, and Yang." ° Usually, 3-aminopropyl-functionalized silica was employed as the parent support. In most studies, ethylenediamine-based PAMAM was constructed via the approach developed for solution by Tomalia and pioneered on solid support by Bradley. 

In a number of cases, PAMAM dendrons were also prepared on other polymer particle cores, such as alumina, chitosan, cellulose, zirconia-urea-formaldehyde resin, silica-coated magnetite, and carbon nanotubes. Like the silica support (see above), at least in the case of the chitosan, the theoretically predicted propagation of the dendrons was not achieved, presumably due to the steric hindrance in the support pores. 

Bidentate ligands were used by Alper and coworkers. The bis(diphenylphospino-methyl)amine ligands were prepared on primary amine-terminated PAMAM dendrons on silica as well as polyamido dendrons on polystyrene via the double Mannich-like reaction with formaldehyde and diphenylphosphine (Scheme 15.36a). " Subsequently, Alper and coworkers subjected the dendronized ligand-decorated supports to complexation with rhodium and palladium precursors in order to prepare active catalysts for a number of important chemical transformations (Scheme 15.36b). Initially, the dendronized rhodium catalysts were tested in the hydroformylation reaction and carbonylative ring expansion of... 

Iminophenols immobilized on PAMAM dendronized polystyrene and cellulose were used by Lei and coworkers to tether Sn complexes, forming active catalysts for the Baeyer-Villiger oxidation of ketones (Scheme 15.41). Probably due to the already mentioned difficulty in building fully branched PAMAM dendrons on solid support, the catalytic activity decreased with the generations. This tendency was diminished by preparing the dendritic catalysts on macroporous polystyrene, particularly that with a high... 

PAMAM dendrons on insoluble support can themselves serve as basic catalysts due to their multiple tertiary and primary amine sites, as demonstrated by Kapoor et al. on silica and by Sreekumar and coworkers on polystyrene." ° " PAMAM promoted the Knoeve-nagel condensation and ring opening of epoxides by aniline. The catalytic systems on polystyrene demonstrated a positive dendritic effect, possibly as a result of generating a special isolated environment near the catalytic sites. 

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