Synthesis and Properties of Heavy Chalcogen Analogues of the Texas Reds and Related Rhodamines

Abstract

Analogues of Texas red incorporating the heavy chalcogens S, Se, and Te atoms in the xanthylium core were prepared from the addition of aryl Grignard reagents to appropriate chalcogenoxanthone precursors. The xanthones were prepared via directed metalation of amide precursors, addition of dichalcogenide electrophiles, and electrophilic cyclization of the resulting chalcogenides with phosphorus oxychloride and triethylamine. The Texas red analogues incorporate two fused julolidine rings containing the rhodamine nitrogen atoms. Analogues containing two “half-julolidine” groups (a trimethyltetrahydroquinoline) and one julolidine and one “half-julolidine” were also prepared. The photophysics of the Texas red analogues were examined. The S-analogues were highly fluorescent, the Se-analogues generated single oxygen (1O2) efficiently upon irradiation, and the Te-analogues were easily oxidized to rhodamines with the telluroxide oxidation state. The tellurorhodamine telluroxides absorb at wavelengths ≥690 nm and emit with fluorescence maxima >720 nm. A mesityl-substituted tellurorhodamine derivative localized in the mitochondria of Colo-26 cells (a murine colon carcinoma cell line) and was oxidized in vitro to the fluorescent telluroxide.

Selenorhodamine photosensitizers with the Texas-red core for photodynamic therapy of cancer cells

“…13 Fluorescence quantum yields (U F ) were measured as previously described. 11 Quantum yields for the generation of singlet oxygen [U( 1 O 2 )] were measured as previously described.…”

“…Supplementary data ( 1 H, 13 C, and 31 P NMR spectra and HRMS data for 5 and 6 as PF 6 and chloride salts) associated with this article can be found, in the online version, at http://dx.doi.org/10. 1016/j.bmc.2015.06.006.…”

Nebraska Red: a phosphinate-based near-infrared fluorophore scaffold for chemical biology applications

“…11 An alternative strategy for modulating the emission wavelength of xanthene-based dyes such as rhodamine is to replace the bridging oxygen atom with other elements. Chalcogens like sulfur, selenium, and tellurium 12 along with group 14 elements like carbon, 13 silicon, germanium, and tin 14 have been incorporated in this manner and the resulting fluorophores all display red-shifted excitation and emission spectra compared to the parent rhodamine scaffold. However, this approach can also negatively impact the brightness of the resulting fluorophore in certain cases (Table S1, ESI † ).…”

Selective photodepletion of malignant T cells in extracorporeal photopheresis with selenorhodamine photosensitizers

“…Xanthones 11 and 12 were prepared as previously described. 20 Deprotonation of thiophene derivative 13 18 with LDA gave 2-lithiothiophene 14 , which was then added to THF solutions of 11 and 12 20 at −78 °C (Scheme 1). Workup with aqueous HPF 6 gave 7 and 9 in 88% and 79% isolated yield, respectively, as the PF 6 salts.…”

“…Quantum yields for the generation of 1 O 2 [ Φ ( 1 O 2 )] by 5 – 10 were measured by time-resolved spectroscopy at 1270 nm 20 of 1 O 2 phosphorescence in air-saturated methanol using 2 [ Φ ( 1 O 2 ) = 0.87] 16 as a standard (Fig. S2, Supporting information).…”