Dendrimers assisted synthesis

Figure 7.16 (A) Dendron-capped poly(triacetylene) and, (B) soluble oligothiophenes obtained by dendrimers assisted synthesis...

Stability, and complex formulation procedures, a class of dendritic fluorinated MRl agents, G0-G3, were developed (Figure 7.3). These fluorinated dendrimers, G0-G3, of different sizes are perfect MRl agents for screening, and G2 was identified as a stable and rapidly excreted MRl agent. Here, a fluorous-assisted synthesis of the fluorinated dendrimer G2 and a FMS of four fluorinated dendrimers are selected as examples to illustrate how fluorous synthesis works. 

In order to investigate dendrimers of a different nature [230], Bradley described the synthesis and transfection efficiency of polyamidourea dendrimers synthesised from isocyanate-containing AB3 monomers [231-234]. The use of this kind of tris-branched building block was addressed to enhance dendrimer synthesis by replacement of the 1,4-addition step typical of PAMAM synthesis and to a rapid increase in terminal functionality. The dendritic structures were synthesised using a divergent, microwave-assisted, solid-phase approach with the dendrimers assembled on polystyrene resin via an acid labile linker (see Fig. 26). In particular, a G3.0 polyamidourea bis-dendron with the peripheral amino groups conjugated to L-lysine residues demonstrated remarkable transfection abilities [234],... 

The only mass spectrometric methods available during the era of the first cascade synthesis in 1978 [30] were electron impact (El) and field desorption (FD) mass spectrometry [31]. Fast atom bombardment (FAB) mass spectrometry is limited to fairly low mass ranges and not very suitable for compounds of low polarity. It was not until the development of new and gentle ionisation methods such as MALDI (matrix-assisted laser desorption ionization) [32] and ESI (electrospray ionization) [33] that the conditions were fulfilled for the start of intense research in the field of dendrimer chemistry. The following section will present the special features of these mass-spectrometric methods and their importance in dendrimer analysis. 

Dendrimer- and polymer-supported catalysts can be employed in the ATH of sultam precursors [71, 72], including examples where the supporting material has sulfonyl groups and therefore assists reactions in water [73]. The synthesis of an amphiphilic polystyrene-type immobilized TsDPEN ligand and its application in ATH of cyclic sulfonimines has been reported (Fig. 16) [74]. 

Microwave-assisted reactions for polyamidoatnine (PAMAM) dendrimer synthesis was carried out by Lopez-Andarias et al. (2012). The dendrimers were obtained in good yields, with high purity, and near-perfect regioselectivity while multivalent dendrimeric peptides were synthesized via a microwave-assisted Huisgen 1,3-dipolar cycloaddition between azido peptides and dendrimeric alkynes in relatively good yields (46 to 96%) (Rijkers et al., 2005). 

Later Reymonds group reported the synthesis of dendrimer 45 (Fig. 7.3) that catalyzes ester hydrolysis with a single catalytic histidine residue in the core [36]. According to the author, a pair of arginine residues in the first-generation branch assists substrate binding. 

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