Recent Progress in Small Spirocyclic, Xanthene-Based Fluorescent Probes

Abstract

The use of fluorescent probes in a multitude of applications is still an expanding field. This review covers the recent progress made in small molecular, spirocyclic xanthene-based probes containing different heteroatoms (e.g., oxygen, silicon, carbon) in position 10′. After a short introduction, we will focus on applications like the interaction of probes with enzymes and targeted labeling of organelles and proteins, detection of small molecules, as well as their use in therapeutics or diagnostics and super-resolution microscopy. Furthermore, the last part will summarize recent advances in the synthesis and understanding of their structure–behavior relationship including novel computational approaches.

A CO2-Responsive Imidazole-Functionalized Fluorescent Material Mediates Cancer Chemotherapy

“…Imidazole-functionalised R6G (I-R6G) was obtained through a simple, one-step amidation reaction of R6G with excess 1-(3-aminopropyl)imidazole under mild heating without a catalyst, resulting in a crystalline pink powder with an acceptable yield of 72% ( Scheme 1 a). During the reaction, an intermediate form with an amide bond undergoes intramolecular self-cyclisation to create a spirolactam functional group in the structure of I-R6G, in which an amide group bonds to the C9 atom of the xanthene conjugate group of I-R6G by nucleophilic attack [ 40 , 41 , 42 ], leading to the formation of a bulky heterocyclic aromatic structure. The recrystallised I-R6G exhibited the expected structural features (including molecular structure, weight and elemental composition), as confirmed by Fourier transform infrared (FTIR), proton/carbon nuclear magnetic resonance ( 1 H- and 13 C-NMR), mass spectrometry (MS) and elemental analysis (EA) (see Supporting Information for more detail, Figures S1–S4 and Table S1 ).…”

Late‐Stage Amination of Drug‐Like Benzoic Acids: Access to Anilines and Drug Conjugates through Directed Iridium‐Catalyzed C−H Activation

“…While the ketone functionality is in plain with the neighboring C−H functionality and could theoretically serve as a good directing group, no functionalization directed by this group was observed. Fluorescein, a widely used fluorescent tracer, [29] was functionalized in the anticipated position with complete regioselectivity. While the product 2 x is depicted in its ring‐closed lactone form as observed by 1 H NMR spectroscopy, the corresponding starting material would be present in an equilibrium with a ring‐opened form containing a free carboxylate facilitating the directed C−H activation.…”

Synthesis of Novel Diketopyrrolopyrrole-Rhodamine Conjugates and Their Ability for Sensing Cu2+ and Li+

“…Rhodamines are also an important class of fluorescent molecules endowed with high molar absorptivity, intense fluorescence in the visible region, and an effective tuning of fluorescence emission through the spirolactam ring-opening mechanism, which is particularly relevant for designing acid- and metal-ion-sensing probes [ 8 ]. These singular properties make them very useful for many applications, namely as fluorescent markers in biotechnology, chemosensors for small molecule detection, and imaging in medicine [ 9 , 10 , 11 ]. Over the last few years, the design of chemosensors based on a displacement mechanism involving the interaction of an analyte with a specific coordination complex has emerged as a very attractive approach for the preparation of highly sensitive and selective ion chemosensors, with very promising results in real environment samples [ 12 , 13 ] and cell bioimaging [ 14 ].…”