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

Combination of complexes of lanthanide cations (Ln3+) for their luminescent properties and peptides for their recognition properties is interesting in view of designing responsive luminescent probes. The octadentate DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) chelate is the most popular chelate to design Ln3+ complex-peptide conjugates. We describe a novel building block, DO3Apic-tris(allyl)ester, which provides access to peptides with a conjugated nonadentate chelate, namely DO3Apic, featuring a picolinate arm in place of one of the acetate arms compared to DOTA, 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, we compare two luminescent zinc fingers (LZF) comprising (i) a zinc finger peptide for selective Zn2+ binding, (ii) a Eu3+ complex and (iii) an acridone antenna (ACD) for long-wavelength sensitization of Eu3+ luminescence. The first one, LZF3ACD|Eu, incorporates a DOTA chelate for Eu3+ whereas the other, LZF4ACD|Eu, incorporates a DO3Apic chelate. Both act as Zn2+-responsive luminescent probes but we show that changing DOTA for DO3Apic results in a higher Eu3+ 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 Ln3+ complex-peptide conjugates. Additionally, the DO3Apic chelate provides self-calibration for LZF4ACD|Eu luminescence upon excitation of its picolinamide chromophore, making LZF4ACD|Eu a ratiometric sensor for Zn2+. A novel building-block, DO3Apic-tris(allyl)ester (tri-allyl 2,2′,2′-(10-((6-carboxypyridin-2-yl)methyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetate), gives access to nonadentate lanthanide complexes-peptide conjugates for better luminescence properties, as illustrated with a zinc finger peptide and Eu3+-based Zn2+-responsive probe. [Display omitted] •A novel building block for conjugation of a nonadentate chelate to peptides is presented.•This compound is used to prepare a Zn2+-responsive probe based on Eu3+ luminescence.•It provides better luminescence properties compared to octadentate chelates.•It also allows ratiometric detection of zinc via dual-wavelength excitation.