New highly sensitive pH probes for 31P NMR spectroscopy. Spin-lattice relaxation time measurements as a function of molecular structure, temperature, pH, and biological medium.

Abstract : New uncharged a-aminophosphonates derived from diethyl(2- methylpyrrolidin-2-yl) phosphonate were synthesized by nucleophilic addition of dialkylphosphites on 2-methyl-1-pyrroline. These compounds were intended as enhanced 31P-NMR pH probes in biological systems. Compared to standard pH markers such as inorganic phosphate or methylphosphonate, they demonstrated in vitro low acidic pKa values (6.6 < pKa < 7.0), resonance peaks ranging from 21 to 35 ppm, distinct from those of phosphorylated metabolites, and 3e4 times as sensitive (9.2 < Ddab < 9.9 ppm) as usual markers, such as inorganic phosphate or methylphosphonate. The detailed synthetic procedures for three representative new pH probes, which were non-toxic (in the mM range) in rat isolated heart preparations, was reported. In a larger series of 27 structurally related a-aminophosphonates, 1/T1 (31P) values were given in different conditions of milieu, temperature and pH. The data support unique features for these compounds to reveal acidic cellular compartments.