Synthesis of Dendrimers: Convergent and Divergent Approaches
Dendrimers can be prepared by both convergent and divergent approaches. In the convergent approach, first suitable building blocks are prepared and then connected by lego chemistry, ligations or click chemistry. In the divergent approach, the synthesis is
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Synthesis of Dendrimers: Convergent and Divergent Approaches
Dendrimers are available by two major strategies (Fig. 6.1) [33, 37, 68, 113, 144– 146, 179, 182, 186, 195, 200]. First, “the divergent strategy” is based on a growth of a dendron originating from a core site. In this strategy, monomeric modules are assembled in a radial, branch-upon-branch motif using certain dendritic rules and principles. The second method is a “convergent strategy.” It begins from what will become the dendrimer shell inward to a reactive focal point, forming a single reactive dendron. A final dendrimer structure is assembled by reaction of several dendrons with a multifunctional core. Both strategies are significantly improved by “Lego,” click, and ligation chemistries. They are described in individual sections. The synthesis of well-defined multivalent and multimodal dendritic structures and their use for biomedical applications has been reviewed [33, 176, 186]. By possessing major advantages such as cheap reagents, fast synthesis, exponential growth, and possibility to prepare large dendrimers, the divergent approach served as a guidance rule in dendrimer synthesis [5, 18, 30, 32, 33, 37, 41, 52, 99, 113, 119, 144, 147, 179, 181, 182, 194, 200, 211]. However, the divergent approach has also its downsides such as more complicated purification of synthesized compounds caused by the contamination of the product by deletion compounds with molecular weight, charge, polarity, hydrophilicity, etc. very similar to the desired product. Furthermore, the steric hindrance of bulky branches in higher generations of dendrimers suppresses couplings of next building blocks and is responsible for major defects on the dendrimer surface. Whether the cumulative defects of coupling failures has to be avoided, the purification of the growing glycodendrimer in every generation is necessary [5, 18, 30, 32, 33, 41, 52, 99, 119, 147, 179, 181, 182, 186, 194, 200, 211]. In summary, the divergent approach is an easy way for synthesis of dendrimers, especially when empowered either by chemical ligation or connection of carbohydrates and dendrimers with linking bridges. The main advantages of the convergent approach are monodispersity of dendrimers, the accessibility of asymmetric dendrimers through an attachment of different types of dendrons to one core, and facile purification and characterization of the product [5, 18, 30, 32, 33, 37, 41, 52, 76, 99, 113, 119, 144, 147, 148, 155, 179, 181, 182, 186, 194, 200, 211]. The facile purification is based on significant ˇ J. Sebest´ ık et al., Biomedical Applications of Peptide-, Glyco- and Glycopeptide Dendrimers, and Analogous Dendrimeric Structures, DOI 10.1007/978-3-7091-1206-9 6, © Springer-Verlag Wien 2012
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6 Synthesis of Dendrimers: Convergent and Divergent Approaches
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Fig. 6.1 Divergent (a) and convergent (b) strategies for dendrimer syntheses [32, 144, 179, 181, 182, 186, 195, 200]. The figure was reprinted from [186] with kind permission of Springer, Wien–NewYork
differences between the de
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