Bioorthogonal Click and Release Reaction of Iminosydnones with Cycloalkynes

Abstract

We report the discovery of a new bioorthogonal click‐and‐release reaction involving iminosydnones and strained alkynes. This transformation leads to two products resulting from the ligation and fragmentation of iminosydnones under physiological conditions. Optimized iminosydnones were successfully used to design innovative cleavable linkers for protein modification, thus opening up new areas in the fields of drug release and target‐fishing applications. This click‐and‐release technology offers the possibility of exchanging tags on proteins for functionalized cyclooctynes under mild and bioorthogonal conditions.

Selective Engineering of Linkage‐Specific α2,6‐N‐Linked Sialoproteins Using Sydnone‐Modified Sialic Acid Bioorthogonal Reporters

“…To overcome this limitation, we envisaged that sialic acids fitted with a sydnone moiety, an aromatic mesoionic 1,3‐dipole, would be valuable unnatural sugars for addition to the MOE toolbox. We and others have recently shown that sydnones can react in a metal‐free strain‐promoted click fashion with cyclooctyne reagents for the in vitro bioconjugation of purified proteins …”

Design and Synthesis of Iminosydnones for Fast Click and Release Reactions with Cycloalkynes

“…An interesting finding can be highlighted from this study: substituents on position N 6 play a considerable role with respect to the reaction rate of the transformation. As we previously described, amide‐substituted ImSyd 5 a – d and carbamate derivatives 7 a , b are competent substrates but with moderate reactivity (0.004< k <0.018 m −1 sec −1 ). The presence of a more electron‐withdrawing sulfonamide moiety on the other hand increases the rate up to 0.042 m −1 sec −1 for compound 6 b .…”

“…[b] The rate constants were determined under initial rate conditions. Kinetic results of compounds 4 a , 5 a , 6 a , 7 b , 8 a , 8 i and 9 f were described in our previous paper …”

“…We recently reported a preliminary study on the unprecedented reactivity of iminosydnones (ImSyds) and cycloalkynes (Scheme a). In the process, a first [3+2]‐cycloaddition is followed by a retro Diels–Alder step generating a pyrazole “click” product and the concomitant release of the substituent connected to the exocyclic nitrogen of the ImSyd structure . This technology enabled the complete release of a fluorophore from an antibody in blood plasma and the full concomitant recovery and labelling of an immobilized protein under mild and physiological conditions.…”

“…Suzuki coupling with boronic acids or pinacol boranes delivered 9 c in 51 % yield and the vinyl aldehyde 9 d in an excellent 91 % yield. The carbonylation of 7 c in presence of 15 mol % of [PdCl 2 (PPh 3 ) 2 ], triethylamine (TEA) and EtOH delivered in 2.5 hours the desired ester 9 e in 71 % yield . This optimized protocol turned out to be the most effective to introduce a strong electron‐withdrawing substituent on the N 3 position of the ImSyd scaffold, which cannot be otherwise obtained by the standard cyclization procedure (see Figure , compounds 4 f , g ).…”