Degradable Conjugates from Oxanorbornadiene Reagents

Abstract

Oxanorbornadienedicarboxylate (OND) reagents were explored for purposes of binding and releasing drugs from serum albumins as representative macromolecular carriers. Being highly reactive Michael acceptors, ONDs form adducts with thiols and amines, which then undergo retro-Diels–Alder fragmentation. The study of more than 30 model adducts revealed a number of modifications that can be used to influence adduct stability. For the most reactive OND linkers, the labeling of the single available bovine serum albumin (BSA) cysteine residue was complete within minutes at mid-micromolar concentration of reactants. While a selectivity of greater than 1000-fold for thiol over amine was observed with model amino acids, the labeling of protein amines with ONDs is fast enough to be practical, as demonstrated by reaction with thiol-depleted BSA. The OND–amine adducts were found to be up to 15 times more stable than OND–thiol adducts, and to be sensitive to acid by virtue of a stereochemically-dependent acceleration of cycloreversion. The release rate of fluorescent cargo from serum albumins was tuned by selecting the coupling partners: the available half-lives ranged from 40 minutes to 7 days at 37 °C. Such versatility of release profiles from protein carriers, controlled by the nature of the OND linkage, is a useful addition to the drug delivery toolbox.

Click Chemistry in Complex Mixtures: Bioorthogonal Bioconjugation

“…Another alternative to maleimides are electron-deficient oxanorbornadienes (entry 10), which display thiol addition rates similar to those of maleimides, but have greater aqueous stability (Hong et al, 2009a; Kislukhin et al, 2011; Kislukhin et al, 2012). An additional fragmentation feature of this linkage is discussed at the end of this article.…”

“…Another variant on this theme is provided by the aforementioned oxanorbornadiene linkages (Table 4, entry 10). These feature a built-in cleavage trigger, since their Michael adducts undergo retro-Diels-Alder fragmentation at rates predetermined over several orders of magnitude by their substitution pattern (Figure 9C) (Kislukhin et al, 2012). If the resulting furan and thiomaleate moieties do not compromise the function of the released functional molecules, this provides a well-controlled triggered cleavage pathway for drug release.…”

Relative Performance of Alkynes in Copper-Catalyzed Azide–Alkyne Cycloaddition

“…The 2 nd -order rate constant of the conjugate addition of a model cysteine-containing peptide to N -phenylpropiolamide can be estimated as approximately 0.13 M −1 s −1 (pH 7.0). 17 The reaction rates of maleimide 18 and oxanorbornadiene reagents 19,20 with thiols are more than 500 times greater.…”

“Click” reactions in polysaccharide modification

“…their Michael acceptor profiles and retro-Diels-Alder fragmentation tendency [100]. If properly utilized, these two properties may help to generate novel reversible hydrogels or drug delivery systems.…”