Dendrimers iterative preparation

The precise structure subset, dendrimers are prepared using iterative protection-condensation-deprotection reaction cycles. These reiterative cycles incorporate ABn monomers (i.e. branch cell units) into structural domains referred to as dendrons. Assembly of these dendrons can proceed in a divergent [1] (core... 

Scheme 14.1 Schematic diagram showing the iterative preparation of dendrimers.

Scheme 5.8 Schematic representing the iterative preparation of a dendrimer.

The title compound offers two sites for polymerization, both at the silicon center and on the vinyl group. These structural features make Da attractive for polymer chemistry and are exploited in the preparation of thin films and related materials. A related application of Da involves the construction of carbosilane den-drimers by functionalization of the vinyl groups. Each generation of dendrimer is prepared by a two-step iterative process consisting of hydrosilylation followed by addition of allylmagnesium bromide. The silicon unit introduced by hydrosilylation serves as a branch point for further generations. 

Meijer and co-workers also used a divergent dendrimer synthesis to prepare AB diblock structures (Figure 7.13B) in which the polystyrene linear block is used to initiate growth of the polypropylene imine) dendritic block [45], An amino end group had to be introduced in the polystyrene as a core for subsequent growth of the dendritic fragment via an iterative protocol of sequential... 

Its design versatility, as generic dendrons may be prepared to be used later as building blocks in conjunction with other reactive molecules, or coupled to a multifunctional core to afford functional dendrimers, dendritic-linear hybrids, dendronized polymers, etc. This may be a particularly significant advantage if the coupled reactive or core molecule is itself sensitive to the reaction conditions used in the multiple steps of the iterative synthesis of a dendrimer. 

Recently the divergent iterative approach, welt known in oiganic synthesis, has been successfully extended to prepare polynuclear dendrimer-type complexes containing up to 22 metal centers using 2,3-dpp as bridging ligand. The two... 

Less has so far been published about carbohydrate core units [54] than about dendrimers with carbohydrate terminal groups. The first PAMAM dendrimer with a carbohydrate core unit was prepared from the a-D-glycoside 1 as core unit precursor. Up to second-generation PAMAM dendrimers with a D-glucose core could be prepared by iteration Fig. 4.30 shows the first generation [55]. 

Scheme 4.21. Construction of polysiloxane dendrimers prepared by an iterative silane hydroxylation and chloride displacement at silicon.

Scheme 4.38. Iterative procedure for the preparation of dendrimers with flexible pentaerythritol-based cores.

After debenzylation (Pd-C, cyclohexene) of the hypercores (e.g., 25) by transfer hydrogenation, they were treated with aryl branched, benzyl ether dendrons (Scheme 5.6) that were prepared by similar iterative transformations,1271 i.e., benzylic bromination and phenolic O-alkylation (See Section 5.4.2). Thus, hexaphenol core 27 was reacted with six equivalents of the benzylic bromide building block 28 to give the benzyloxy terminated dendrimer 29. Key features of these dendrimers include cores with flexible alkyl spacers and a three-directional, quaternary carbon branching center. 

Scheme 5.29. Moore et al. s[9° iterative procedure for the preparation of poly(aryl alkyne) dendrimers.

The interest in liquid crystals motivated the design of liquid-crystalline dendrimers functionalized with Fc and fullerene (Cso)- Dendrimers 64-66 were prepared by applying a convergent and iterative synthetic methodology. Monodisperse macromolecules were thus obtained. 

Dendrimer-based drug delivery systems have been successful in both improving bioavailability as well as targeting drugs. The main advantages for the use of dendrimers as drug carriers reside in their multivalent design and their well-defined structure that results from the stepwise, iterative approach used in their preparation. The anionic and neutral dendrimers have been shown to be less toxic than the cationic dendrimers but at the same time they suffer from lower permeability compared to cationic dendrimers. Typically the smaller size of dendrimers... 

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