Stabilization of Aliphatic Phosphines by Auxiliary Phosphine Sulfides Offers Zeptomolar Affinity and Unprecedented Selectivity for Probing Biological Cu^I

Abstract

Full elucidation of the functions and homeostatic pathways of biological copper requires tools that can selectively recognize and manipulate this trace nutrient within living cells and tissues, where it exists primarily as CuI. Buffered at attomolar concentrations, intracellular CuI is, however, not readily accessible to commonly employed amine and thioether‐based chelators. Herein, we reveal a chelator design strategy in which phosphine sulfides aid in CuI coordination while simultaneously stabilizing aliphatic phosphine donors, producing a charge‐neutral ligand with low‐zeptomolar dissociation constant and 1017‐fold selectivity for CuI over ZnII, FeII, and MnII. As illustrated by reversing ATP7A trafficking in cells and blocking long‐term potentiation of neurons in mouse hippocampal brain tissue, the ligand is capable of intercepting copper‐dependent processes. The phosphine sulfide‐stabilized phosphine (PSP) design approach, which confers resistance towards protonation, dioxygen, and disulfides, could be readily expanded towards ligands and probes with tailored properties for exploring CuI in a broad range of biological systems.

Copper bioavailability is a KRAS-specific vulnerability in colorectal cancer

“…To corroborate these findings, we used the recently developed ratiometric Cu(I)-selective fluorescent probe, crisp-17, as another readout for bioavailable Cu 25 . The probe was first validated using the cell-permeant complex CuGTSM (glyoxalbis(N 4 -methyl-3-thiosemicarbazonato) copper(II)) and a Cu(I)-specific chelator (PSP-2) 29 , which confirmed that the probe reversibly responds to changes in cellular Cu levels ( Supplementary Fig. 5e, f).…”

Preorganized PSP Ligands Yield Monomeric Cu(I) Complexes with Subzeptomolar Cu(I) Dissociation Constants

“…4−6 While dissociation constants below 1 fM are challenging to realize with commonly employed synthetic Cu(I) chelators based on thioether donors, 7−9 we recently demonstrated that dissociation constants down to 10 zM are attainable with aliphatic phosphine-based ligands containing auxiliary phosphine sulfide moieties. 10 The latter not only participate in Cu(I) coordination but also exert an electron-withdrawing effect on the phosphine sites, thus stabilizing the free ligand against protonation and oxidation. These phosphine sulfide-stabilized phosphines, typified by PSP-1 and PSP-2 (Chart 1), maintain strong Cu(I) coordinating ability despite dramatically reduced basicity compared to typical aliphatic phosphines.…”

“…With a 1:1 Cu(I) complex stability constant of log K = 20.0 (K d = 10 zM), PSP-2 offers an unprecedented Cu(I) affinity among synthetic ligands and is unaffected by Mn(II), Fe(II), or Zn(II), even at millimolar concentrations. 10 The Cu(I) complexes of both PSP-1 and PSP-2, however, engage in additional dimerization equilibria at high micromolar concentrations, hampering the utility of these ligands for applications where Cu(I) availability must be precisely controlled. We previously obtained an X-ray crystal structure of the dimeric PSP-1-Cu I complex, which revealed only two fused 5-membered chelate rings per Cu(I) center as opposed to the triple ring fusion that would be expected in a C 3 -symmetric 1:1 Cu(I) complex.…”

“…We previously obtained an X-ray crystal structure of the dimeric PSP-1-Cu I complex, which revealed only two fused 5-membered chelate rings per Cu(I) center as opposed to the triple ring fusion that would be expected in a C 3 -symmetric 1:1 Cu(I) complex. 10 This suggests that relief of steric strain imposed by triple ring fusion is the driving force for dimerization. A similar strain effect has been noted for tris(2-pyridylmethyl)phosphine, which coordinates to Fe(II), Ru(II), and Cr(III) only through a tridentate N 2 P donor set, with the third pyridine moiety left uncoordinated.…”

“…The phenPS stability constant was further verified by direct competition with MCL-1, as previously described for PSP-2 (Figure S9). 10 Electrochemistry. The redox potentials of phenPS and naphPS and the copper complexes were determined by cyclic voltammetry in methanol containing 0.1 M Bu 4 NPF 6 using a CH Instruments potentiostat (model 600A).…”