Dendrimers chemoselectivity

Larre C, Donnadieu B, Caminade AM, Majoral JP (1998) Phosphorus-containing dendrimers chemoselective functionalization of internal layers. J Am Chem Soc 120 4029-4030... 

Such a methodology is also useful for the chemoselective functionalization of internal voids of dendrimers. This can be accomplished for example by adding 2 equiv. of allyl, propargyl or phosphonate trifluoromethane sulfonate on the dendrimer of generation 1 71-lGj] (Scheme 34). Functionalization occurs on the sulfur atom of the two P=N-P(S) units with the quantitative formation of the... 

Persson PV, Casas J, Iversen T, Cordova A (2006) Direct organocatalytic chemoselective synthesis of a dendrimer-like star polyester. Macromolecules 39 2819-2822... 

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 ... 

Innine ligation of unprotected peptides is based on the chemoselectivity between a weak base and an aldehyde to form either a stable imine or an imino intermediate that can isomerize rapidly to a more stable product. Whereas the thiol ligations are optimally performed at neutral or basic pH, imine ligations are performed under acidic conditions, which is highly desirable because under acidic conditions the basic side-chain nucleophiles of an unprotected peptide are protonated to be excluded from the reaction. Furthermore, these two reaction conditions can be exploited for ligating dissimilar peptide chains to a core to form heteromeric peptide dendrimers.11401... 

Chemoselective polyalkylation of phosphorus-based dendrimers offers an opportunity to produce cationic dendrimers from neutral ones [66]. 

The chemoselective character of this reaction permits the use of unprotected glycosyl thiols.92 With a similar strategy, an unprotected sugar derivative has been linked to 2-mercaptoacetyl-functionalized dendrimer forming a disulfide bond.93... 

Tam, J. P. and Spetzler, J. C. (1995) Chemoselective approaches to the preparation of peptide dendrimers and branched artificial proteins using unprotected peptides as building blocks. Biomedical Peptides, Proteins Nucleic Acids 1, 123-132. 

Chemoselective reaction with a diamine followed by q anuric chloride in a subsequent step provides the next larger intermediate. Iteration leads to materials that can be dimerized. Dimerizing the molecule shown would provide a G2 dendrimer with eight end groups. 

Such a strategy has been used in peptide synthesis and, more recently, for den-drimer synthesis. Since the first report by Frechet et al. in 1995 on a chemoselective approach to a low-generation dendron, by combining carbamate/etherification reactions [19], several combinations of chemistries have been suggested for producing dendrimers in fewer reaction steps. 

Figure 7 Graphical representation of the number of steps required to grow a dendrimer using a chemoselective accelerated approach (top) as compared to a traditional divergent approach (bottom). ...

Scheme 7 Chemoselective AB2 + CD2 approach to making a fourth-generation Frechet-type dendrimer in four steps." ...

Maity P, Yamazoe S, Tsukuda T. Dendrimer-encapsulated copper cluster as a chemoselective and regenerable hydrogenation catalyst. ACS Catal 2013 3 182-5. 

By encapsulation of the trialkylphosphine-modified rhodium catalyst into zeolites, the high chemoselectivity was maintained but the Hb ratio in the product alcohol could be increased by as much as 10 times [65]. Anchoring of trialkylphos-phines to carbosilane dendrimers based on polyhedral silsesquioxane (POSS) produced dendrimeric ligands, which in the hydroformylation-hydrogenation of 1-octene preferentially produced linear alcohols. Regioselectivity exceeded that achieved with the low molecular ligand [66]. 

Ratheesh Kumar, V. K. and K. R. Gopidas. Palladium nanoparticle-cored Gl-dendrimer stabilized by carbon-Pd bonds Synthesis, characterization and use as chemoselective, room temperature hydrogenation catalyst. Tetrahedron Lett. 52, 2011 3102-3105. 

Using Cu nanoparticles encapsulated in the sixth-generation PAMAM dendrimer, an excellent chemoselectivity of C=0 versus C=C was demonstrated on the... 

Fig. 4.17 A copper cluster encapsulated within a PAMAM dendrimer with hydroxyl surface groups (PAMAM-OH) acting as a chemoselective catalyst for hydrogenation of carbonyl and olefin groups in water. The activity was dependent on the molar ratio of the Cu and PAMAM-OH used in the synthesis, which was ascribed to the size-specific chemical properties of the Cu clusters. The dendrimer-encapsulated Cu cluster was oxidized into Cu ions under aerobic conditions, but it could be regenerated by reduction with NaBH4 for use in catalytic applications. Reprinted with permission from ref. [103]. Copyright 2013 American Chemical Society...

Figure 8.2 General scheme for the divergent synthesis of bis(MPA)-type dendrimers using a combination of CuAAC and traditional esterification reactions, as synthesized by Malkoch et al (Antoni et ah, 2007). (Reproduced from P. Antoni, D. Nystrom, C.J. Hawker et ah, A chemoselective approach for the accelerated synthesis of well-defined dendritic architectures, Chemical Communications, 22, 2249-2251, 2007, by permission of the Royal Society of Chemistry.)...

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