Dendrimers have several unique properties that make them attractive scaffolds for use in biomedical applications. To date, multivalent and multimodal dendritic structures have been synthesized predominantly by statistical modification of peripheral groups. However, the potential application of such probes in patients demands well-defined and monodisperse materials that have unique structures. Current progress in the field of chemical biology, in particular chemoselective ligation methods, renders this challenge possible. In this Minireview, we outline the different available synthetic strategies, some applications that already make use of this new generation of multivalent and multimodal architectures, and the challenges for future developments.

Site-specific immobilization of peptides and proteins is crucial to ensure their functionality in surface-based assays. We report the use of aniline-catalyzed oxime ligations as a very efficient and broadly applicable method to covalently attach the N terminus of proteins and peptides to a surface functionalized with alkoxy-amine groups.

In vivo selection of phage libraries that display random peptide sequences on their surface has yielded a number of peptides that specifically home to tumor tissue. In this study, two different peptides are introduced to synthetic dendritic scaffolds via oxime chemistry and the resulting compounds are analyzed for tumor homing. Modification of the dendritic wedge with a short, linear peptide that homes to clotted plasma proteins showed that a specific receptor in tumor tissue is recognized, but that the extravasation is likely affected by the size of the construct. In contrast, a positively charged cyclic peptide with cell penetrating properties was capable of directing the entire dendritic architecture toward a specific receptor in tumor lymphatics. These observations are in agreement with results previously reported for micelles and nanoparticles and emphasize the influence of peptide properties and overall size on the biodistribution of multivalent macromolecules.

A general methodology for the synthesis of multifunctional AB 2 , AB 3 , AB 4 , and AB 5 dendritic wedges is described based on an orthogonal protection strategy. Asymmetric polyamide dendrons that possess N-terminal cysteine residues at the periphery were quantitatively functionalized with C-terminal thioester peptides using native chemical ligation. Conjugation of biologically relevant groups at the focal point resulted

The covalent synthesis of complex biomolecular systems such as multivalent protein dendrimers often proceeds with low efficiency, thereby making alternative strategies based on noncovalent chemistry of high interest. Here, the synthesis of protein dendrimers using a strong but noncovalent interaction between a peptide and complementary protein is proposed as an efficient strategy to arrive at dendrimers fully functionalized with protein domains. The association of S-peptide to S-protein results in the formation of an active enzyme (ribonuclease S) and therefore serves as an ideal system to explore this synthetic approach. Native chemical ligation was used to couple four S-peptides by means of their C-terminal thioester to a cysteine-functionalized dendritic scaffold, thus yielding a tetravalent S-peptide wedge. A fully functional ribonuclease S tetramer was prepared by addition of four equivalents of S-protein. Biophysical techniques (isothermal titration calorimetry (ITC), surface plasmon resonance (SPR), and mass spectrometry) and an enzymatic activity assay were used to verify the formation of the multivalent complex. The noncovalent synthetic strategy presented here provides access to well-defined, dynamic, semisynthetic protein assemblies in high yield and is therefore of interest to the field of nanomedicine as well as biomaterials.