Novel Sterically Crowded and Conformationally Constrained α-Aminophosphonates with a Near-Neutral pKa as Highly Accurate 31P NMR pH Probes. Application to Subtle pH Gradients Determination in Dictyostelium discoideum Cells

Abstract

In order to discover new 31P NMR markers for probing subtle pH changes (<0.2 pH unit) in biological environments, fifteen new conformationally constrained or sterically hindered α-aminophosphonates derived from diethyl(2-methylpyrrolidin-2-yl)phosphonate were synthesized and tested for their pH reporting and cytotoxic properties in vitro. All compounds showed near-neutral pKas (ranging 6.28–6.97), chemical shifts not overlapping those of phosphorus metabolites, and spectroscopic sensitivities (i.e., chemical shifts variation Δδab between the acidic and basic forms) ranging from 9.2–10.7 ppm, being fourfold larger than conventional endogenous markers such as inorganic phosphate. X-ray crystallographic studies combined with predictive empirical relationships and ab initio calculations addressed the inductive and stereochemical effects of substituents linked to the protonated amine function. Satisfactory correlations were established between pKas and both the 2D structure and pyramidalization at phosphorus, showing that steric crowding around the phosphorus is crucial for modulating Δδab. Finally, the hit 31P NMR pH probe 1b bearing an unsubstituted 1,3,2-dioxaphosphorinane ring, which is moderately lipophilic, nontoxic on A549 and NHLF cells, and showing pKa = 6.45 with Δδab = 10.64 ppm, allowed the first clear-cut evidence of trans-sarcolemmal pH gradients in normoxic Dictyostelium discoideum cells with an accuracy of <0.05 pH units.

Conformational Analysis of 1,5-Diaryl-3-Oxo-1,4-Pentadiene Derivatives: A Nuclear Overhauser Effect Spectroscopy Investigation

“…Within the frequency range of 3 to 5 ppm, there are a total of seven NMR signals associated with the CH2 groups of the diethyl(phenyl)methylphosphonate (H21a, H21b, H22a, and H22b) and oxypiperidine (H2 Upon analyzing the chemical shifts of NMR signals in the 1 H spectra, it was seen that there are two signals in the high field region corresponding to the methyl groups of diethyl(phenyl)methylphosphonate (H23 and H24) [35]. Within the frequency range of 3 to 5 ppm, there are a total of seven NMR signals associated with the CH 2 groups of the diethyl(phenyl)methylphosphonate (H21a, H21b, H22a, and H22b) and oxypiperidine (H2 and H6) fragments [36,37]. Additionally, there is a signal for the CH group (H7) bonded to the nitrogen atom of piperidine.…”

Synthesis, Characterization, and Docking Study of Novel Thioureidophosphonate-Incorporated Silver Nanocomposites as Potent Antibacterial Agents

“…On top of this, α-aminophosphonates (α-APs), as a significant class of organophosphorus compounds, were remarkably exploited in several amplified domains [ 34 , 35 ]. Lately, α-APs have captivated researchers’ interests in numerous applicable dimensions such as wastewater treatment [ 36 , 37 ], rare earth metal removal [ 38 , 39 ], catalysis [ 40 ], sensing [ 41 ], flame retardancy [ 42 ], agrochemical technology [ 35 , 42 ], and corrosion inhibition [ 43 ]. Moreover, α-APs have had unprecedented success in several medical arenas, such as antioxidant, antifungal, anti-HIV agents, antimicrobial, anticancer, antiviral, peptidomimetics, and enzyme inhibitors [ 34 , 35 , 44 ].…”