The Eschenmoser's Salt as a Formylation Agent for the Synthesis of Indolizinecarbaldehydes and Their Use for Colorimetric Nitrite Detection

C-H bond formylation is the most immediate way to incorporate the versatile formyl group into (hetero)aromatics. However, the type of reagents and severe conditions involved in the classical formylation methods often curtail their application, especially in the presence of other functional groups. Herein, we present the Eschenmoser's salt, a commercially available (dimethylamino)methylating chemical, as a useful reagent for the C-H formylation of indolizines and other compounds. The method is straightforward and mild, furnishing indolizinecarbaldehydes in modest-to-good yields with exclusive and remote regioselectivity. Furthermore, these compounds can be easily transformed into push-pull dyes and are highly selective in the colorimetric detection of nitrite, a substance extensively employed as preservative in the food industry, the concentration of which is crucial to control to prevent harmful effects in living organisms. The assay is simple, allowing the naked-eye detection of nitrite in solution or on a cotton swab for a wide range of concentrations.

Fluorous Phase-Enhanced Fluorescent Sensitivity for Enantioselective Recognition of Lysine

A novel fluorinated chiral dialdehyde (S,S)-1, prepared from (S,S)- or (R,R)-2,6-bis(1-hydroxyethyl)pyridine and 2-naphthol containing a highly fluorinated alkyl group, is found to show enantioselective and chemoselective fluorescent recognition of lysine in the fluorous phase. We discovered that the fluorous phase greatly enhances the fluorescent sensitivity and selectivity of the probe. Thus, the fluorous phase not only can allow the fluorescence measurement to be conducted away from common organic and aqueous media to minimize undesirable interference but also can provide a unique environment to greatly improve the selective fluorescent response.

Chemoselective and Enantioselective Fluorescent Identification of Specific Amino Acid Enantiomers

The enantiomers of chiral amino acids play versatile roles in biological systems including humans. They are also very useful in the asymmetric synthesis of diverse chiral organic compounds. Therefore, identification...

Recent advances of BINOL-based sensors for enantioselective fluorescence recognition

Enantioselective fluorescent sensors show large potential for fast, real-time, and highly sensitive measurement of the concentration and enantiomeric composition of chiral molecules. Among all of the sensors, BINOL-based sensors have been actively investigated and extensively used to carry out highly enantioselective, sensitive recognition of chiral α-hydroxycarboxylic acids, amino acids, amino acid derivatives, amino alcohols and amines. In this manuscript, the recent progress of chiral BINOL-based sensors for enantioselective fluorescence recognition of different substrates is reviewed and discussed. The structure of BINOL is tuned by introducing various groups or molecules which systematically changed its fluorescence properties and offered potential for rapid assays of chiral organic molecules. From the development of this area, we gain fresh insight into the challenges and chances of BINOL-based sensors.

Enantioselective Fluorescent Recognition of Free Amino Acids: Challenges and Opportunities

Fluorescent probes that can discriminate enantiomers of amino acids in organic media or aqueous solution are discussed. This Minireview focuses on recent progress in the studies of three classes of probes including those made of cyclodextrins, 1,1'-binaphthyl compounds, and nanomaterials, and uses them to illustrate the design strategies, applications, and limitations in this area. These probes are potentially useful for rapid analysis of asymmetric reactions for amino acid synthesis as well as the real-time imaging of amino acids in biological systems. The challenges in these applications are analyzed. Working in this field of enantioselective fluorescent recognition of amino acids offers great opportunities to make new scientific discoveries and to develop important practical applications.

Pd(0)-catalyzed amination in the synthesis of chiral derivatives of BINAM and their evaluation as fluorescent enantioselective detectors

A mini-review covers recent successes in the synthesis of (S)-1,1′-binaphthyl-2,2′-diamine (BINAM) using Pd(0)-catalyzed amination reactions. As a result, versatile compounds with C2-chiral backbone were synthesized, among them are derivatives bearing additional chiral amino and fluorophore groups like dansyl amide, 7-methoxycoumarin, 6-aminoquinoline, different macrocyclic compounds with oxadiamine and polyamine linkers were obtained as well. BINAM derivatives of various structures were evaluated as fluorescent enantioselective detectors for a series of model amino alcohols. Many of them were shown to be efficient in sensing certain enantiomers of the amino alcohols by selective changes in the emission in the presence of these analytes. Small changes in the structure of the BINAM derivatives lead to serious difference in the recognition ability of the compounds under investigation.

Opposite Enantioselectivity of Mg(II) Versus Zn(II) in the Fluorescent Recognition of Amino Acids

The addition of Mg²⁺ is found to turn on the fluorescence response of a molecular probe, 3,3'-diformyl-1,1'-bi-2-naphthol, toward chiral amino acids with high enantioselectivity. It is further found that the enantioselective fluorescence responses of the molecular probe in the presence of Mg²⁺ toward certain amino acids are the opposite of those in the presence of Zn²⁺, that is, using Mg²⁺ with an l-amino acid generates much greater fluorescence enhancement than with the corresponding d-amino acid, but using Zn²⁺ with the d-amino acid gives much greater fluorescence than with the l-enantiomer. Thus, simply changing the metal cation additive allows the chirality sense of the fluorescence-based molecular recognition to be easily regulated.

Zn(ii) promoted dramatic enhancement in the enantioselective fluorescent recognition of functional chiral amines by a chiral aldehyde

The addition of Zn²⁺ to the methanol solution of a BINOL-based chiral dialdehyde leads to dramatically enhanced enantioselective fluorescent responses toward various functional chiral amines, representing one of the first chiral aldehydes capable of such recognition.