Dendron Building Blocks for Click Chemistry

Dendrimers offer a new possibility to derivatize small molecules, surfaces or biopharmaceuticals with a monodisperse macromolecule and alter in this way properties like solubility and hydrophilicity. Immunogenicity and pharmacokinetics of pharmaceuticals will be improved. The synthetic approach for designing these dendrons of different generations is based on 2,2-bis(hydroxymethyl) propionic acid, which is a non-toxic and biocompatible building block.

The size can be designed from 250 g/mole for 1st generation dendrons to over 4400 g/mole with 5th generation compounds. Dendrimers can be designed reaching even a molecular weight of some 10.000 Da. As focal point alkyne and azido functions are used with appropriate counter parts in any type of click chemistry reaction. Olefinic functions offer the possibility for addition reaction or conjugation by metathesis reactions or photo reactions with the aid of UV light. For the modification of Gold surfaces sulphur bearing dendrons can be used, they also conjugate with biologicals via disulfide bridge formation.

Hydroxyl and acetonide functions are available as terminal groups. Thus the surface can be designed as either hydrophilic or hydrophobic. In particular the hydrophobic acetonide variations offers through its amphiphilic nature interesting properties, as the centre is still polar and hydrophilic. This improves solubility in biological liquids. The hydrophobic surface helps to interact with lipids, cell surfaces, and hydrophobic enzymes, like lipases. Furthermore, the acetonides offer another advantages for chemical diversity. They can be removed and thus be a temporary protecting group for further derivatization of the dendritic surface.

Literature:

• Wu P, Malkoch M, Hunt JN, et al.; Multivalent, bifunctional dendrimers prepared by click chemistry; Chem. Commun. 2005; 46: 5775-5777. DOI: 10.1039/b512021g.
• Antoni P, Malkoch M, Vamvounis G, et al. ; Europium confined cyclen dendrimers with photophysically active triazoles; J. Mater. Chem. 2008; 18(22): 2545-2554.
• E. R. Gillies and J. M. J. Fréchet, Drug Discovery Today 2005; 10: 35.
• Dual Labeling of Biomolecules by Click Chemistry: a Sequential Approach. P. Kele, G. Mezö, D. Achatz, O. S. Wolfbeis, Angew. Chem. 2009; 121: 350-353; Angew. Chem. Intl. Ed. 2009; 48: 344-347. DOI: 10.1002/ange.200804514.

Carbohydrates for Click Chemistry

Protein and lipid glycosilation is a life-governing and omnipresent process. Glycoconjugates display a multitude of biological effects from protein folding and stabilization, energy storage, cell surface interaction through molecular recognition motifs for cell-cell communication, and structural support and protection. Defective metabolic pathways in pathological processes, inflammation and microbial virulence, neurodegenerative conditions tumour metastasis are only a few key words indicating the many possible application fields. The smooth and selective reaction conditions of the Click reaction open so far impossible molecule design for drug development and vaccine development based on carbohydrate conjugation.

General References:

• A. Varki, R. Cummins, J. Esko, H. Freeze, G. Hart, J. Marth, eds. Essentials of glycobiology, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, New York, 1999.
• R.S. Haltiwanger, J.B. Lowe; Role of Glycosilation in Development; Annu. Rev. Biochem. 2004; 73: 491-537.
• .M. Ruud, T. Elliott, P. Cresswell, I.A. Wilson, R.A. Dwek; Glycosilation in Immune System; Science 2001; 291(5512): 2370-2375.
• K. Othsubo, J.D. Marth, Glycosilation in Cellular Mechanisms of Health and Disease; Cell 2006; 126(5): 855-867.
• K. Ley; The role of selectins in inflammation and disease; Trends in Mol. Med. 2003; 9(6): 263-268.
• A. Hölemann, P.H.Seeberger; Carbohydrae diversity: synthesis of glycoconjugates and complex carbohydrates; Chem. Opin. Biotech. 2004; 15(6): 615-622.
• G. Walsh, R. Roy Jefferis; Post-translational modifications in the context of therapeutic proteins. Nature Biotechnol. 2006; 24(10): 1241-1252.
• Z. Shriver, S. Raguram, R. Sasisekharan; Glycomics: A pathway to a class of new and improved therapeutics. Nat. Rev. Drug Discov. 2004; 3(10): 863-873.
• A. Dove; The bittersweet promise of glycbiology; Nature Biotechnol. 2001; 19(10): 913-917.

Literature Arrays & Carbohydrates:

• Sun et al., Bioconjugate Chem. 2006; 17(1): 52-57.
• Bryan et al., J. Am. Chem. Soc. 2004; 126: 8640-8641.

Literature: Dendrimers & Carbohydrates:

• Wu et al., Chem. Commun. 2005; 46: 5775-5777.

Literature: Peptide Antibiotics Modification with Carbohydrates:

• Lin et al., J. Am. Chem. Soc. 2004; 126: 13998-14003.

Click Chemistry in DNA/RNA Synthesis

Due to its unique bioorthogonality the Click reaction is very useful also in any oligonucleotide synthesis. Simple or no workup and purification of the product are further advantages. However, the use of this method for DNA modification has been somewhat delayed by the fact that copper ions damage DNA, typically yielding strand breaks [1]. As these problems have now been overcome by the use of copper(I)-stabilizing ligands (e.g. tris(benzyltriazolylmethyl)amine, TBTA [2], Carell et al. and Seela et al. discovered that the CuAAC reaction can be used to functionalize alkyne-modified DNA nucleobases with extremely high efficiency [3,4].

A broad field of applications opens by using DNA Click components:

• DNA and RNA labelling: incorporation of alkyne-phosphoramidites in oligos followed by labelling with azido markers [7];
• PCR assays, PCR primers and labelling of large fragments with alkyne triphosphates in nucleotide mixtures; labelling PCR-fragments with azido markers [8];
• Dendron Building Blocks for Click Chemistry
• Microarrays with phosphoramidites, triphosphates or oligonucleotides to set up microarrays;
• Nanoparticles, Bioconjugation.

References:

• C. J. Burrows, J. G. Muller, Chem. Rev. 1998; 98: 1109 – 1151.
• T. R. Chan, R. Hilgraf, K. B. Sharpless, V. V. Fokin, Org. Lett. 2004; 6: 2853 – 2855.
• J. Gierlich, G. A. Burley, P. M. E. Gramlich, D. M. Hammond, T. Carell, Org. Lett. 2006; 8:Chem. Biodiversity 2006; 3: 509-514.
• P. M. E. Gramlich, S. Warncke, J. Gierlich, T. Carell, Angew. Chem. 2008; 120:Angew. Chem. Int. Ed. 2008; 47: 3442– 3444.
• New labelling strategies for the sensitive detection of analytes; Patent WO2006/117161.
• Helv. Chim. Acta 2007; 90: 535-552.
• K. Gutsmiedl, P. M. E. Gramlich, A. Schmidt, G. Burley, T. Carell, Chem. Eur. J. 2007; 13:Angew. Chem. Int. Ed. 2008; 47: 3442-3444.
• Synthesis of Highly Modified DNA by a Combination of PCR with Alkyne-Bearing Triphosphates and Click Chemistry. J. Gierlich, K. Gutsmiedl, P. M. E. Gramlich, A. Schmidt, G. Burley, T. Carell, Chem. Eur. J. 2007; 13: 9486-9494. 3639-3642. F. Seela, V. R. Sirivolu, 3491–3493; 9486-9494.