A novel DOTA-like building block with a picolinate arm for the synthesis of lanthanide complex-peptide conjugates with improved luminescence properties

Abstract

Combination of complexes of trivalent lanthanide cations (Ln 3+) for their luminescent properties and peptides for their recognition properties or folding abilities is interesting in view of designing responsive luminescent probes. The octadentate DOTA chelate is the most popular chelate to design luminescent Ln 3+ complex-peptide conjugates. In this article, we describe a novel building block, DO3Apic-tris(allyl)ester, which provides access to peptides with a conjugated nonadentate chelate, namely DO3Apic, featuring a cyclen macrocycle functionalized by three acetate and one picolinamide arms, for improved luminescence properties. This building block, with allyl protecting groups, is readily obtained by solid phase synthesis. We show that it is superior to its analogue with tBu protecting groups for the preparation of peptide conjugates because of the difficult removal of the tBu protecting groups for the latter. Then, two Zn 2+-responsive luminescent probes, which rely on (i) a zinc finger scaffold for selective Zn 2+ binding, (ii) a Eu 3+ complex and (iii) an acridone antenna for long-wavelength sensitization of Eu 3+ luminescence, are compared. One of these probes, LZF3 ACD|Eu , incorporates a DOTA chelate whereas the other, LZF4 ACD|Eu , incorporates a DO3Apic chelate. We show that changing the octadentate DOTA for the nonadentate DO3Apic ligand results in a higher Eu 3+ luminescence lifetime and in a doubling of the quantum yield, confirming the interest of the DO3Apic chelate and the DO3Apic(tris(allyl)ester building block for the preparation of Ln 3+ complex-peptide conjugates. Additionally, the DO3Apic chelate provides self-calibration for LZF4 ACD|Eu luminescence upon excitation of its picolinamide chromophore, making LZF4 ACD|Eu a ratiometric sensor for Zn 2+ detection.

Bioinspired Luminescent Europium-Based Probe Capable of Discrimination between Ag+ and Cu+

“…The shape of the Eu 3+ emission spectrum remains unchanged upon Cu + and Ag + binding as well as the Eu 3+ emission decay lifetime (Eu  0.63 ms, Table1). Such a lifetime value is typical of a mono-hydrated (q = 1) Eu 3+ ion bound to a DOTAmonoamide chelate[42][43][44] as confirmed by the experimental determination of q for LCC4 Eu and Ag•LCC4 Eu (FigureS3and TableS1in SI). Interestingly, Ag + binding induces a 2.5-fold enhancement of intensity of the sensitized Eu 3+ emission (ex = 283 nm) while Cu + decreases it by 50 % (Figure 3C, right).…”

Ratiometric Luminescence Detection of Copper(I) by a Resonant System Comprising Two Antenna/Lanthanide Pairs

“…That of Eu 3+ decreases slightly from 0.67 to 0.61 ms. These values are typical of a monohydrated Eu 3+ –DOTA–monoamide complex. , More interestingly, the value of τ Tb for LCCR TbEu is 0.89 ms, which is much shorter than the one of LCC1 Tb , 1.98 ms, typical of monohydrated Tb 3+ –DOTA–monoamide complexes. , Nevertheless, determination of the hydration number ( q ) of Tb 3+ and Eu 3+ evidenced a single Ln-bound water molecule for both lanthanides, as expected with the DOTA–monoamide ligand (details in the Supporting Information). During the Cu + titration, τ Tb increases from 0.89 to 0.98 ms, a value reached at 1.0 equiv of Cu + that remains constant in the presence of excess Cu + (Figure D).…”

“…These values are typical of a monohydrated Eu 3+ −DOTA− monoamide complex. 17,18 More interestingly, the value of τ Tb for LCCR TbEu is 0.89 ms, which is much shorter than the one of LCC1 Tb , 1.98 ms, 20 typical of monohydrated Tb 3+ − DOTA−monoamide complexes. 17,44 Nevertheless, determination of the hydration number (q) of Tb 3+ and Eu 3+ evidenced a single Ln-bound water molecule for both lanthanides, as expected with the DOTA−monoamide ligand (details in the Supporting Information).…”

“…We are interested in developing luminescent probes for metal cations or biomolecules based on peptides and luminescent trivalent lanthanides (Ln 3+ ). − Lanthanides display desirable luminescent properties for biological applications, which comprise (i) line-like emission bands ranging from the visible to the near-infrared (NIR), (ii) large Stokes shift, (iii) long luminescence lifetimes (allowing suppression of background fluorescence in time-resolved detection), and (iv) excellent photostability. − Because f–f transitions are forbidden by the Laporte rules, direct excitation of Ln 3+ is inefficient (ε < 10 M –1 cm –1 ). Efficient lanthanide luminescence relies on the so-called “antenna effect”: an organic chromophore (the antenna) is used as a light-harvesting device to transfer, after excitation, electronic energy to the Ln 3+ in order to populate its emissive excited state.…”

Luminescent Peptide/Lanthanide(III) Complex Conjugates with Push–Pull Antennas: Application to One- and Two-Photon Microscopy Imaging

“…These protected chelators generally lack an antenna moiety, which requires introduction of a remote antenna somewhere else on the peptide to create luminescent probes. Recently, we have described the DO3Apic- tris ( t Bu)­ester and DO3Apic- tris (allyl)­ester protected chelates suitable for the preparation of peptide/Ln 3+ complex conjugates with a picolinate Ln 3+ -coordinating moiety able to act as an antenna to sensitize Ln 3+ luminescence . However, absorption of the picolinate moiety is far in the UV with a maximum at 280 nm, which is not suitable for most biological applications, especially cellular imaging.…”