Dendrimers formation

Fig. 23. Formation of various 2nd-generation dendrimers or dendritic compounds using branch building blocks of (S)- or (.Reconfiguration at the benzylic centers [90], Three of the eight combinations tested by us led to dendrimer formation (products 63,65,66) while five halted at the stage of the doubly coupled products 64,70-73, cf. Fig. 22. Core molecule 69 has less hindered OH groups and is, of course, not an isomer of 54 and ent-54...

Figure 7.6 The divergent and convergent synthesis methods of dendrimer formation.

This section concludes with a description of tandem synthetic strategies (Section 14.1.6) in which sequential reactions involve combinations of steps such as dendrimer formations combined with cyclic peptides (Section 14.1.6.1), chemoselective cyclization combined with divergent syntheses (Section 14.1.6.3), and many thiol-based reactions and cyclizations (Sections 14.1.6.4—14.1.6.7) J18 ... 

Ligation Conditions of Peptide Dendrimer Formation through Oxime, Hydrazone, and Thiazolidine Ligations To Form 64, 66, or 70 [85 ... 

Carbohydrate structures can also act as a scaffold for dendrimer formation. The polysubstituted sugar 23 (Fig. 5) has been synthesized and shown that it can act as a scaffold onto which peptide sequences can be assembled to form another novel vaccine system (15). The development of this carbohydrate scaffold technology and its application to vaccine and gene delivery is under way. The synthesis of 23 is complex a complete account of the procedures can be found in ref. 15. 

Viau L, Willis AC et al (2007) Ruthenium cluster chemistry monodentate bis(diphenylphosphino)acetylene-ligated cluster modules in chain and dendrimer formation. J Organomet Chem 692 2086-2091... 

In addition to alkyl-substituted derivatives, soluble PPPs 6 are also known today containing alkoxy groups as well as ionic side groups (carboxy and sulfonic acid functions) [18]. Schliiter et al. recently described the generation of soluble PPPs decorated with densely packed stcrically demanding dendrons on the formation of cylindrically shaped dendrimers, so-called cylinder dendrimers ] 19]. 

Relatively simple NMR techniques have been employed to obtain useful information about dendrimers. For example, the formation of one generation from its immediate predecessor containing NH groups has been followed by NMR. As coupling proceeds, the chemical shifts of the NH protons become shifted to lower field (higher frequency), a shift that is consistent with coupling at the NH groups within the branches. 

It is possible to take advantage of the differing characteristics of the periphery and the interior to promote chemical reactions. For example, a dendrimer having a non-polar aliphatic periphery with highly polar inner branches can be used to catalyse unimolecular elimination reactions in tertiary alkyl halides in a non-polar aliphatic solvent. This works because the alkyl halide has some polarity, so become relatively concentrated within the polar branches of the dendrimer. This polar medium favours the formation of polar transition states and intermediates, and allows some free alkene to be formed. This, being nonpolar, is expelled from the polar region, and moves out of the dendrimer and into the non-polar solvent. This is a highly efficient process, and the elimination reaction can be driven to completion with only 0.01 % by mass of a dendrimer in the reaction mixture in the presence of an auxiliary base such as potassium carbonate. 

The reaction of the first-generation dendron 29 with the core, which is a trin-uclear platinum complex (30) bridged by 1,3,5-triethynylmesitylene, in a molar ratio of 3 1 resulted in the formation of the first-generation dendrimer (31). Since the reaction proceeded quantitatively and no side products were observed, the first-generation dendrimer was easily isolated by alumina column chromatography. 

Scheme 12. Reversible formation of cationic metal-acetylide dendrimers 39 and 40...

As an extension of this work,Kaifer et al. prepared a series of PPI dendrimers (G-l-G-4) functionalized with cobaltocenium at the periphery [48] and studied their electrochemical behavior and binding interactions with P-CD. While the positively charged cobaltocenium-terminated dendrimer 27G-1 is not com-plexed by P-CD in aqueous media, electrochemical reduction of the dendrimer in the presence of excess P-CD triggers the formation of a multisite inclusion complex with this host to provide pseudorotaxane-terminated dendrimer 28G-1 (Fig. 10). Similar electrochemical and binding behavior toward P-CD was observed for the G-2 and G-3 dendrimers. However, the resulting multisite inclu-... 

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