Lipidated cyclopropenes via a stable 3-N spirocyclopropene scaffold

Abstract

Lipidated cyclopropenes serve as useful bioorthogonal reagents for imaging cell membranes due to the cyclopropene’s small size and ability to ligate with pro-fluorescent tetrazines. Previously, the lipidation of cyclopropenes required modification at the C3 position because methods to append lipids at C1/C2 were not available. Herein, we describe C1/C2 lipidation with the biologically active lipid ceramide and a common phospholipid using a cyclopropene scaffold whose reactivity with 1,2,4,5-tetrazines has been caged.

Caged Cyclopropenes with Improved Tetrazine Ligation Kinetics

“…We obtained the acid from ester 12 , which, in turn, was obtained via n -BuLi-mediated iodo-orthoformate S6 (Scheme S5) substitution in 75% yield. To the best of our knowledge, this is the only method to directly install an ester functionality onto C1/C2 of a cyclopropene . Moreover, ketal-ester 12 upon saponification and acid workup directly afforded ketone cyclopropene 13 in 62% yield.…”

“…To the best of our knowledge, this is the only method to directly install an ester functionality onto C1/C2 of a cyclopropene. 40 Moreover, ketal-ester 12 upon saponification and acid workup directly afforded ketone cyclopropene 13 in 62% yield. Ketone 3-N cyclopropene acid 13 can be easily appended to amines.…”

Live‐Cell Imaging of Sterculic Acid—a Naturally Occurring 1,2‐Cyclopropene Fatty Acid—by Bioorthogonal Reaction with Turn‐On Tetrazine‐Fluorophore Conjugates**

“…[40] We were curious whether this oleic acid analogue could be used in live-cell compatible labelling chemistry, as it is known to be biologically stable and represents a minimal structural modification of one methylene compared to the parent oleic acid structure. Furthermore, all previously described bioorthogonal IED-DA applications have been explored for cyclopropenes with 1,3-, 3,3-or 1,2,3-substitution patterns, [31,32,41] whereas there has been no report of a 1,2-substituted cyclopropene as a bioorthogonal probe.…”

Live‐Cell Imaging of Sterculic Acid—a Naturally Occurring 1,2‐Cyclopropene Fatty Acid—by Bioorthogonal Reaction with Turn‐On Tetrazine‐Fluorophore Conjugates**

“…[40] We were curious whether this oleic acid analogue could be used in livecell compatible labelling chemistry, as it is known to be biologically stable and represents a minimal structural modification of one methylene compared to the parent oleic acid structure. Furthermore, all previously described bioorthogonal IEDDA applications have been explored for cyclopropenes with 1,3-, 3,3-or 1,2,3-substitution patterns [31,32,41] , whereas there has been no report of a 1,2-substituted cyclopropene as a bioorthogonal probe. Here, we explore the use of 1 as a bioorthogonal reagent, assessing both its ligation kinetics, short-term toxicity and liveand fixed-cell imaging capacity.…”