title: "Reduced" Coumarin Dyes with an O-Phosphorylated 2,2-Dimethyl-4-(hydroxymethyl)-1,2,3,4-tetrahydroquinoline Fragment: Synthesis, Spectra, and STED Microscopy.
abstract: Large Stokes-shift coumarin dyes with an O-phosphorylated 4-(hydroxymethyl)-2,2-dimethyl-1,2,3,4-tetrahydroquinoline fragment emitting in the blue, green, and red regions of the visible spectrum were synthesized. For this purpose, N-substituted and O-protected 1,2-dihydro-7-hydroxy-2,2,4-trimethylquinoline was oxidized with SeO2 to the corresponding α,β-unsaturated aldehyde and then reduced with NaBH4 in a "one-pot" fashion to yield N-substituted and 7-O-protected 4-(hydroxymethyl)-7-hydroxy-2,2-dimethyl-1,2,3,4-tetrahydroquinoline as a common precursor to all the coumarin dyes reported here. The photophysical properties of the new dyes ("reduced coumarins") and 1,2-dihydroquinoline analogues (formal precursors) with a trisubstituted C=C bond were compared. The "reduced coumarins" were found to be more photoresistant and brighter than their 1,2-dihydroquinoline counterparts. Free carboxylate analogues, as well as their antibody conjugates (obtained from N-hydroxysuccinimidyl esters) were also prepared. All studied conjugates with secondary antibodies afforded high specificity and were suitable for fluorescence microscopy. The red-emitting coumarin dye bearing a betaine fragment at the C-3-position showed excellent performance in stimulation emission depletion (STED) microscopy.
authors.affiliation: Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany.
authors.forename: Shamil
authors.initials: S
authors.lastname: Nizamov
authors.affiliation: Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany.
authors.forename: Maksim V
authors.initials: MV
authors.lastname: Sednev
authors.affiliation: Laboratorio de Nanoscopias Fotonicas, INQUIMAE-DQIAyQF (FCEyN), Universidad de Buenos Aires & Conicet, Buenos Aires, Argentina.
authors.forename: Mariano L
authors.initials: ML
authors.lastname: Bossi
authors.affiliation: Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany.
authors.forename: Elke
authors.identifier: http://orcid.org/0000-0002-6509-2191
authors.initials: E
authors.lastname: Hebisch
authors.affiliation: Institute for Organic and Biomolecular Chemistry, Georg-August University, Tammannstrasse 2, 37077, Göttingen, Germany.
authors.forename: Holm
authors.initials: H
authors.lastname: Frauendorf
authors.affiliation: Heart Research Center Göttingen, Department of Cardiology & Pulmonology, University Medical Center Göttingen, 37077, Göttingen, Germany.
authors.forename: Stephan E
authors.identifier: http://orcid.org/0000-0002-8115-3513
authors.initials: SE
authors.lastname: Lehnart
authors.affiliation: Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany. vbelov@gwdg.de.
authors.forename: Vladimir N
authors.identifier: http://orcid.org/0000-0002-7741-4653
authors.initials: VN
authors.lastname: Belov
authors.affiliation: Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany. shell@gwdg.de.
authors.forename: Stefan W
authors.initials: SW
authors.lastname: Hell
mesh_terms: D003374:Coumarins / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D010766:Phosphorylation; D011804:Quinolines / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: D003374:Coumarins; D005456:Fluorescent Dyes; D011804:Quinolines
keywords: STED microscopy; bioconjugation; coumarins; dyes/pigments; fluorescence