Efficient Pictet-Spengler Bioconjugation with N-Substituted Pyrrolyl Alanine Derivatives.

We discovered N-pyrrolyl alanine derivatives as efficient reagents for the fast and selective Pictet-Spengler reaction with aldehyde-containing biomolecules. Other aldehyde-labeling methods described so far have several drawbacks, like hydrolytic instability, slow reaction kinetics or not readily available labeling reagents. Pictet-Spengler cyclizations of pyrrolyl 2-ethylamine substituted at the pyrrole nitrogen are significantly faster than with analogues substituted at the α- and ß- position. Functionalized N-pyrrolyl alanine derivatives can be synthesized in only 2-3 steps from commercially available materials. The small size of the reagent, the high reaction rate, and the easy synthesis make pyrrolyl alanine Pictet-Spengler (PAPS) an attractive choice for bioconjugation reactions. PAPS was shown as an efficient strategy for the site-selective biotinylation of an antibody as well as for the condensation of nucleic-acid derivatives, demonstrating the versatility of this reagent.

Synthesis of DNA conjugates with metalated tetracationic porphyrins by postsynthetic cycloadditions.

Tetracationic porphyrins of the TMPP (meso-tetra-(4-N-methylpyridyl)porphyrin) type, metalated with Cu(II) or with Au(III), were conjugated covalently to oligonucleotides. The Cu(I)-catalyzed cycloaddition (between an azide and an ethynyl group) and the Diels-Alder cycloaddition (between a furan and a maleimide functionality) were successfully applied as two alternative postsynthetic methods to modify the 2'-position of an internal uridine. Melting temperatures and UV/vis absorption properties were compared. CD measurements indicated that the type of conjugation chemistry determines the grade of intercalation of the attached and positively charged porphyrins.

Development of a metal-ion-mediated base pair for electron transfer in DNA.

A new C-nucleoside structurally based on the hydroxyquinoline ligand was synthesized that is able to form stable pairs in DNA in both the absence and the presence of metal ions. The interactions between the metal centers in adjacent Cu(II)-mediated base pairs in DNA were probed by electron paramagnetic resonance (EPR) spectroscopy. The metal-metal distance falls into the range of previously reported values. Fluorescence studies with a donor-DNA-acceptor system indicate that photoinduced charge-transfer processes across these metal-ion-mediated base pairs in DNA occur more efficiently than over natural base pairs.