Ester-stabilized phosphorus ylides as protonophores on bilayer lipid membranes, mitochondria and chloroplasts

Triphenylphosphonium ylides are commonly used as key intermediates in the Wittig reaction. Based on the known acidities of stabilized ylide precursors, we proposed that a methylene group adjacent to phosphorus in these compounds can ensure proton shuttling across lipid membranes. Here, we synthesized (decylox- ycarbonylmethyl)triphenylphosphonium bromide (CMTPP-C10) by reaction of triphenylphosphine with decyl bromoacetate. This phosphonium salt precursor of the ester-stabilized phosphorus ylide along with its octyl (CMTPP-C8) and dodecyl (CMTPP-C12) analogues was found to be a carrier of protons in mitochondrial, chlo- roplast and artificial lipid membranes, suggesting that it can reversibly release hydrogen ions and diffuse through the membranes in both zwitterionic (ylide) and cationic forms. The CMTPP-C10-mediated electrical current across planar bilayer lipid membranes exhibited pronounced proton selectivity. Similar to conventional proto- nophores, known to uncouple electron transport and ATP synthesis, CMTPP-Cn (n=8, 10, 12) stimulated mitochondrial respiration, while decreasing membrane potential, at micromolar concentrations, thereby showing the classical uncoupling activity in mitochondria. CMTPP-C12 also caused dissipation of transmembrane pH gradient on chloroplast membranes. Importantly, CMTPP-C10 exhibited substantially lower toxicity in cell cul- ture, than C12TPP. Thus, we report the finding of a new class of ylide-type protonophores, which is of substantial interest due to promising therapeutic properties of uncouplers.

Automated summary

This article describes a new method of proton transport across lipid membranes using a synthesized precursor of triphenylphosphonium ylide. The precursor was found to release protons in mitochondrial, chloroplast, and artificial lipid membranes, suggesting its potential as a proton carrier. The new ylide-type protonophores show promising therapeutic properties as uncouplers.