Protonophoric and mitochondrial uncoupling activity of aryl-carbamate substituted fatty acids.

Aryl-urea substituted fatty acids are protonophores and mitochondrial uncouplers that utilise a urea-based synthetic anion transport moiety to carry out the protonophoric cycle. Herein we show that replacement of the urea group with carbamate, a functional group not previously reported to possess anion transport activity, produces analogues that retain the activity of their urea counterparts. Thus, the aryl-carbamate substituted fatty acids uncouple oxidative phosphorylation and inhibit ATP production by collapsing the mitochondrial proton gradient. Proton transport proceeds via self-assembly of the deprotonated aryl-carbamates into membrane permeable dimeric species, formed by intermolecular binding of the carboxylate group to the carbamate moiety. These results highlight the anion transport capacity of the carbamate functional group.

Aryl urea substituted fatty acids: a new class of protonophoric mitochondrial uncoupler that utilises a synthetic anion transporter.

Respiring mitochondria establish a proton gradient across the mitochondrial inner membrane (MIM) that is used to generate ATP. Protein-independent mitochondrial uncouplers collapse the proton gradient and disrupt ATP production by shuttling protons back across the MIM in a protonophoric cycle. Continued cycling relies on the formation of MIM-permeable anionic species that can return to the intermembrane space after deprotonation in the mitochondrial matrix. Previously described protonophores contain acidic groups that are part of delocalised π-systems that provide large surfaces for charge delocalisation and facilitate anion permeation across the MIM. Here we present a new class of protonophoric uncoupler based on aryl-urea substituted fatty acids in which an acidic group and a π-system are separated by a long alkyl chain. The aryl-urea group in these molecules acts as a synthetic anion receptor that forms intermolecular hydrogen bonds with the fatty acid carboxylate after deprotonation. Dispersal of the negative charge across the aryl-urea system produces lipophilic dimeric complexes that can permeate the MIM and facilitate repeated cycling. Substitution of the aryl-urea group with lipophilic electron withdrawing groups is critical to complex lipophilicity and uncoupling activity. The aryl-urea substituted fatty acids represent the first biological example of mitochondrial uncoupling mediated by the interaction of a fatty acid and an anion receptor moiety, via self-assembly.