TY - JOUR

T1 - Heterocycloalkynes Fused to a Heterocyclic Core

T2 - Searching for an Island with Optimal Stability-Reactivity Balance

AU - Danilkina, Natalia A.

AU - Govdi, Anastasia I.

AU - Khlebnikov, Alexander F.

AU - Tikhomirov, Alexander O.

AU - Sharoyko, Vladimir V.

AU - Shtyrov, Andrey A.

AU - Ryazantsev, Mikhail N.

AU - Bräse, Stefan

AU - Balova, Irina A.

N1 - Publisher Copyright: ©

PY - 2021/10/13

Y1 - 2021/10/13

N2 - In the search for fundamentally new, active, stable, and readily synthetically accessible cycloalkynes as strain-promoted azide-alkyne cycloaddition (SPAAC) reagents for bioorthogonal bioconjugation, we integrated two common approaches: the reagent destabilization by the increase of a ring strain and the transition state stabilization through electronic effects. As a result new SPAAC reagents, heterocyclononynes fused to a heterocyclic core, were created. These compounds can be obtained through a general synthetic route based on four crucial steps: the electrophile-promoted cyclization, Sonogashira coupling, Nicholas reaction, and final deprotection of Co-complexes of cycloalkynes from cobalt. Varying the natures of the heterocycle and heteroatom allows for reaching the optimal stability-reactivity balance for new strained systems. Computational and experimental studies revealed similar SPAAC reactivities for stable 9-membered isocoumarin- and benzothiophene-fused heterocycloalkynes and their unstable 8-membered homologues. We discovered that close reactivity is a result of the interplay of two electronic effects, which stabilize SPAAC transition states (πin∗ → σ∗ and π∗ → πin*) with structural effects such as conformational changes from eclipsed to staggered conformations in the cycloalkyne scaffold, that noticeably impact alkyne bending and reactivity. The concerted influence of a heterocycle and a heteroatom on the polarization of a triple bond in highly strained cycles along with a low HOMO-LUMO gap was assumed to be the reason for the unpredictable kinetic instability of all the cyclooctynes and the benzothiophene-fused oxacyclononyne. The applicability of stable isocoumarin-fused azacyclononyne IC9N-BDP-FL for in vitro bioconjugation was exemplified by labeling and visualization of HEK293 cells carrying azido-DNA and azido-glycans.

AB - In the search for fundamentally new, active, stable, and readily synthetically accessible cycloalkynes as strain-promoted azide-alkyne cycloaddition (SPAAC) reagents for bioorthogonal bioconjugation, we integrated two common approaches: the reagent destabilization by the increase of a ring strain and the transition state stabilization through electronic effects. As a result new SPAAC reagents, heterocyclononynes fused to a heterocyclic core, were created. These compounds can be obtained through a general synthetic route based on four crucial steps: the electrophile-promoted cyclization, Sonogashira coupling, Nicholas reaction, and final deprotection of Co-complexes of cycloalkynes from cobalt. Varying the natures of the heterocycle and heteroatom allows for reaching the optimal stability-reactivity balance for new strained systems. Computational and experimental studies revealed similar SPAAC reactivities for stable 9-membered isocoumarin- and benzothiophene-fused heterocycloalkynes and their unstable 8-membered homologues. We discovered that close reactivity is a result of the interplay of two electronic effects, which stabilize SPAAC transition states (πin∗ → σ∗ and π∗ → πin*) with structural effects such as conformational changes from eclipsed to staggered conformations in the cycloalkyne scaffold, that noticeably impact alkyne bending and reactivity. The concerted influence of a heterocycle and a heteroatom on the polarization of a triple bond in highly strained cycles along with a low HOMO-LUMO gap was assumed to be the reason for the unpredictable kinetic instability of all the cyclooctynes and the benzothiophene-fused oxacyclononyne. The applicability of stable isocoumarin-fused azacyclononyne IC9N-BDP-FL for in vitro bioconjugation was exemplified by labeling and visualization of HEK293 cells carrying azido-DNA and azido-glycans.

KW - FREE CLICK CHEMISTRY

KW - COPPER-FREE

KW - NICHOLAS REACTION

KW - 1,3-DIPOLAR CYCLOADDITIONS

KW - MEDIATED SYNTHESIS

KW - KINETIC STABILITY

KW - IN-VIVO

KW - STRAIN

KW - ACTIVATION

KW - BENZOTHIOPHENE

UR - http://www.scopus.com/inward/record.url?scp=85117234545&partnerID=8YFLogxK

UR - https://www.mendeley.com/catalogue/7c75995b-0c1b-37db-b2fe-9e21d827e159/

U2 - 10.1021/jacs.1c06041

DO - 10.1021/jacs.1c06041

M3 - Article

AN - SCOPUS:85117234545

VL - 143

SP - 16519−16537

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 40

ER -