Sequence-Specific, Dynamic Covalent Crosslinking in Aqueous Media

Abstract

This article describes an associating system that integrates the specificity of multiple hydrogen bonding and the strength of dynamic covalent interactions. Linear oligoamides that sequence-specifically pair into H-bonded duplexes in nonpolar solvents were modified with S-trityl groups, allowing the reversible formation of disulfide bonds. The disulfide-crosslinking reactions of oligoamides capable of pairing via two, four, and six intermolecular H-bonds, along with several control strands, were examined using ESI, MALDI-TOF, reverse phase HPLC, and two-dimensional NMR. Results from these studies demonstrate that this system possesses both the high fidelity of multiply H-bonded assemblies and the high stability of covalent interaction, leading to the sequence-specific crosslinking of complementary oligoamides in not only nonpolar (methylene chloride) solutions but also highly competitive (aqueous) media. Experiments were designed to systematically probe the mechanism behind the specific formation of the sequence-matched products, which revealed a thermodymically controlled process. Multiple pairs in the same solution were crosslinked in a sequence-specific fashion. In addition, a length-dependent selectivity was also observed. Thus, oligoamides with different lengths or sequences did not crosslink into mismatched products. As few as two H-bonds is sufficient to bias the specific formation of the crosslinked product in aqueous media, suggesting that associating units with tunable sizes, high stability, and high specificity can be conveniently designed. The combination of H-bonding and dynamic covalent interactions represents a new, generalizable strategy for developing highly specific molecular associating units that are stable in a wide variety of media. These associating units will greatly facilitate the construction of various structures with many applications.

Advances in Bioconjugation

“…Disulfides are, however, susceptible to reduction by biological reducing agents, like glutathione. Hence, the use of disulfides is limited to in vitro applications, such as the crosslinking [77,78] and immobilization [79] of peptides and proteins. Thiol–disulfide interchange is also the basis of an innovative tethering method that enables the identification of small-molecule fragments that bind to specific regions of a target protein [80].…”

Covalent Capture: Merging Covalent and Noncovalent Synthesis

“…[126,127] Very recently, it was shown by Gong and co-workers that the combined use of hydrogen bonds and dynamic covalent bonds results in the spontaneous formation of discrete structures in water, where the hydrogen bonds induce sequence-selectivity. [128,129] Oligoamides 8 and 9 associate in nonpolar media to give a highly stable duplex 8·9 held together by six hydrogen bonds (Figure 11). The complementary arrangement of hydrogen-bond donors and acceptors in 8 (DADDAD) and 9 (ADAADA) ensures that the heteroduplex 8·9 is the only product.…”

“…The importance of the recognition event was even more evident from a subsequent experiment in which six oligoamides (present as three couples of complementary strands with the ability to form either 2, 4, or 6 hydrogen bonds) were mixed in an equimolar ratio. [129] Although a large number of duplexes could be formed statistically, at thermodynamic equilibrium each strand had exclusively dimerized with its complementary partner. This phenomenon is called selfsorting, which refers to the situation in which a system under thermodynamic control displays a nonstatistical composition.…”

“Covalent Capture”: Verschmelzung von kovalenter und nichtkovalenter Synthese

“…Erst kürzlich zeigten Gong et al, dass durch ein Zusammenwirken von Wasserstoffbrücken und dynamischen kovalenten Bindungen spontan diskrete Strukturen in Wasser entstehen können, bei denen die Wasserstoffbrücken eine Sequenzselektivität erzeugen 128. 129 Die Oligoamide 8 und 9 aggregieren in nichtpolaren Medien zu dem sehr stabilen Doppelstrang 8 ⋅ 9 , der von sechs Wasserstoffbrücken zusammengehalten wird (Abbildung 11). Die komplementäre Anordnung von Wasserstoffbrückendonoren und ‐akzeptoren in 8 (DADDAD) und 9 (ADAADA) stellt sicher, dass der Heterodoppelstrang 8 ⋅ 9 das einzige Produkt ist.…”