Zinc Photocages with Improved Photophysical Properties and Cell Permeability Imparted by Ternary Complex Formation

Abstract

Photocaged complexes have demonstrated efficacy as tools to control the availability of bioactive metals in cells to interrogate signaling pathways. We describe the synthesis of two new photocages, {bis [(2-pyridyl)methyl]amino}(9-oxo-2-xanthenyl)acetic acid (XDPAdeCage, 1) {bis[(2-pyridyl)methyl]amino}(m-nitrophenyl)acetic acid (DPAdeCage, 2), which utilize a 4-xanthone acetic acid and meta-nitrobenzyl chromophore respectively, to mediate a photodecarboxylation reaction. Both photocages strongly coordinate Zn 2+ and the binding equilibrium shifts significantly toward free Zn 2+ upon the decarboxylation of the chelator. XDPAdeCage photolyzes with quantum yield of 27% with 365 nm light, and binds Zn 2+ with 4.6 pM affinity, which decreases by over 4 orders of magnitude upon uncaging. A neutral form of [Zn(XDPAdeCage)] + can be generated in situ using the anionic bidentate ligand pyrithione, which imparts membrane impermeability to the ternary complex. Using fluorescent imaging, we have confirmed transport of Zn 2+ across lipophilic membranes; in addition, RT-PCR experiments demonstrate the photocaged complexes ability to perturb cellular processes after photolysis by showing a change in the expression levels of metallothionein and zinc transporter proteins. File list (2) download file view on ChemRxiv March_22 Manuscript.pdf (734.69 KiB) download file view on ChemRxiv March_22 SI.pdf (5.45 MiB)

Using photocaging for fast time-resolved structural biology studies

“…Other metal complexes can also be used for photocaging. For example, zinc complexes (Table 7, compound 4) can be cleaved using 365 nm illumination with quantum yields of 0.27, releasing Zn 2+ and CO 2 (Basa et al, 2015(Basa et al, , 2019. Rhodium(III) and copper(II) complexes have been shown to bind DNA and release it with light of 455-610 nm wavelength for rhodium(III) and 312-694 nm wavelength for copper(II) (Schatzschneider, 2010).…”

Improved photodecarboxylation properties in zinc photocages constructed using m-nitrophenylacetic acid variants

“…We are developing decarboxylation reactions of metanitrophenylacetatic acid (mNPA) and xanthone (XAN) groups to design photocages that release Zn 2+ upon irradiation with light. 1,2 Such photocaged complexes block the biological activity of metal ions until the Zn 2+ release is initiated by exposure to light of a specific wavelength. 3 We recently described DPAdeCage (1) and XDPAdeCage (2), two Zn 2+ photocages that incorporate a dipyridyl amine (DPA) chelating group to selectively bind Zn 2+ over other common loosely bound metal ions found in cells (Error!…”

“…1,2 Such photocaged complexes block the biological activity of metal ions until the Zn 2+ release is initiated by exposure to light of a specific wavelength. 3 We recently described DPAdeCage (1) and XDPAdeCage (2), two Zn 2+ photocages that incorporate a dipyridyl amine (DPA) chelating group to selectively bind Zn 2+ over other common loosely bound metal ions found in cells (Error! Reference source not found.).…”

“…Reference source not found.). 2 Irradiation at or near the max initiates a photoreaction that results in the loss of the carboxylic acid functional group as CO2, which shifts the Zn 2+ binding equilibrium toward unbound metal ion (Scheme 1). The transformation from a 4-coordinate to a 3coordinate chelator leads to a 10 5 -fold reduction in binding affinity (Kd).…”

“…The mass peaks observed in the LC/MS spectrum of 3a-f after photolysis indicate tolyl and aldehyde derivatives analogous to those previously observed with mNPA-based photocages predominate the photoproducts (Scheme 1). 1,2 Compounds containing EDGs (3f-3i) exhibit a bathochromic shift in max compared to the parent compound 3e; however only 3f retained photodecarboxylation activity. The hydroxy compound 3g exhibits a higher (2989 M -1 , cm -1 ) and a more red-shifted absorbance (max = 427 nm) but lacks photoactivity compared to the corresponding methoxy derivative (3f).…”