Dendritic core

The use of dendritic cores in star polymer synthesis by NMP, ATRP and RAFT polymerization was mentioned in Section 9.9.1, In this section wc describe the synthesis of multi-generation dendritic polymers by an iterative approach. 

GPC distributions 553 mechanisms 551 4 precursors 549, 551 microgcl formation 554-5 seif-condensing v iuyl polymerization 555-6 shell-erossjinking of micelles 555 dendritic cores 556-7 thiocarbonvltbio RAFT agents 464, 501-2, 505-14... 

Other types of branched peptide dendrimers, known as multiple antigen peptides (MAPs), have been synthesized to mimic proteins for applications, for instance as synthetic vaccines, serodiagnostics, peptide inhibitors and intracellular delivery vehicles. Since this concept has been recently described in detail elsewhere [11], only the conceptual framework will be briefly presented here. Tam and coworkers have developed a dendritic core based on lysine units for the construction of MAPs [12-15] (Fig. 3). Carrying antigens at their periphery these MAPs have been designed to increase antigenicity and immunogenicity of peptides. 

A number of groups have reported the preparation and in situ application of several types of dendrimers with chiral auxiliaries at their periphery in asymmetric catalysis. These chiral dendrimer ligands can be subdivided into three different classes based on the specific position of the chiral auxiliary in the dendrimer structure. The chiral positions may be located at, (1) the periphery, (2) the dendritic core (in the case of a dendron), or (3) throughout the structure. An example of the first class was reported by Meijer et al. [22] who prepared different generations of polypropylene imine) dendrimers which were substituted at the periphery of the dendrimer with chiral aminoalcohols. These surface functionalities act as chiral ligand sites from which chiral alkylzinc aminoalcoholate catalysts can be generated in situ at the dendrimer periphery. These dendrimer systems were tested as catalyst precursors in the catalytic 1,2-addition of diethylzinc to benzaldehyde (see e.g. 13, Scheme 14). 

Cho B-K, Jain A, Nieberle J, Mahajan S, Wiesner U, Gruner SM, Tuerk S, Raeder HJ. Synthesis and self-assembly of amphiphihc dendrimers based on ahphatic polyether-type dendritic cores. Macromolecules 2004 37 4227-4234. 

II. Oi anometallic Dendrimers Constructed From Oiganosilicon Dendritic Cores. .154... 

II. ORGANOMETALLIC DENDRIMERS CONSTRUCTED FROM ORGANOSILICON DENDRITIC CORES... 

Three different synthetic routes have been developed for the incorporation of ferrocenyl moieties onto organosilicon dendritic cores, which are shown in Scheme 2. The first method involved reactions of the tetra- and octafunctionalized GlClj... 

Scheme 2. Preparation of ferrocenyl-containing dendrimers using organosilicon dendritic cores.

Compared to conventional convergent synthesis, the two-stage method promises fast access to higher-generation monodisperse dendrimers, combined with a jump in terminal functionalities, since the surface functionalities of the hypercore are subject to less steric hindrance than in the case of simple non-dendritic core building blocks of conventional convergent synthesis. Moreover, this approach permits the formation of dendrimers with different inner and outer branching units (layer-block dendrimers) [10,13]. 

In other work, Dandliker et al. have reported the inclusion of iron porphyrins within dendrimers to serve as functional mimics of redox-based proteins (Dandliker et al., 1994, 1995, 1997). These redox-switchable porphyrins show that the Fe3+/Fe2+ redox couple can be altered by the polarity of the surrounding environment. By changing the polarity imposed by the tightly packed branches of the dendritic core, the authors have illustrated that electrochemical behavior can be controlled by slight and subtle through-space environmental factors. These mimics may potentially model a wide variety of redox-driven enzymes and possibly provide mechanistic insights into their function. 

C Extended amphiphilic dendron 6000 1.05 Docosyl periphery 47 Dendritic core + PEO 53 -... 

Two interesting reports by Chan and co-workers of dendritic core-functionalized Ru-BINAP (BINAP = 2,2/-bis(diphenylphosphino)-l,l/-binaphthyl) catalysts, which were employed in asymmetric hydrogenations and which were fully recoverable, have appeared recently [40,41]. In particular, such dendrimers containing long alkyl chains in the periphery were synthesized and... 

In this work we present hyperbranched polymers as platforms for catalysts that fall into three major classes, according to their topology and binding mode to the polymeric support (Fig. 2) (i) defined multiple site catalysts (ii) dendritic core-shell catalysts (iii) supramolecular catalyst complexes. 

The library synthetic pathway is depicted, where the dendritic structure shown in Figure 7.24 is simplified as a single functional site rather than the actual eight carried by the dendritic core. Coupling with a protected amino acid (A, I, or F, first monomer set) and deprotection produced a resin bound amine which was amidated with y- or <5-ketoacids (second monomer set) and finally cyclized with substituted phenylhydrazines (third monomer set) to give the dendrimer bound indoles. These were cleaved by heating at 50°C with methanolic triethylamine, producing the pure library pools in solution (total yield >60%, HPLC purity >85%). 

I have reviewed, in Chapter No. 12, the activation of arenes by the strongly electron-withdrawing 12-electron fragment CpFe+, isolobal to Cr(CO)3 and Mn(CO)3+, and its application to the synthesis of dendritic cores, dendrons, dendrimers, and metallodendrimers, including molecular batteries. 

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