Biotin as acylating agent in the Friedel-Crafts reaction. Avidin affinity of biotinyl derivatives of ferrocene, ruthenocene and pyrene and fluorescence properties of 1-biotinylpyrene

Combining bioinspired nanochannels with ferrocene doped MoS2 nanoplates: Application to ratiometric electrochemical detection of let-7a

Sensitive and accurate detection of tumor suppressor genes is vastly important to the related therapeutic research. Herein, a ratiometric electrochemical method for let-7a detection was established by integrating a ferrocene (Fc) doped MoS₂ nanoplates modified electrode into the nanochannels-based biosensing platform. The ratiometric signal was developed by the redox current of methylene blue (MB) which reflects the target recognition occurred into the nanochannels and the redox current of Fc which corrects the slight signal deviation caused by some analyte-independent factors. And thus, the ratio of peak current of MB and Fc (I_MB/I_Fc) measured at differential pulse voltammogram varied precisely with the increment of the concentration of let-7a incubated in the bioinspired nanochannels. The strategy of spherical DNAzyme induced deposition in nanochannels was utilized to further amplify the signal. Under optimal conditions, a wide linear dynamic range of 50 aM to 10 pM spanning five orders of magnitude was obtained. The developed electrochemical method, with attomole level of detection limit, was successfully applied to the determination of let-7a in human serum and tumor cells. The study not only offers a new route for reliable nucleic acid detection, but also provides an excellent opportunity to extend the application of the two-dimensional transition-metal dichalcogenides.

Synthesis and Biological Activity of Ferrocenyl and Ruthenocenyl Analogues of Etoposide: Discovery of a Novel Dual Inhibitor of Topoisomerase II Activity and Tubulin Polymerization

Two series of the ferrocenyl and ruthenocenyl analogues of etoposide bearing 1,2,3-triazolyl or aminoalkyl linker were synthesized and evaluated for their cytotoxic properties, influence on the cell cycle, ability to induce tubulin polymerization, and inhibition of topoisomerase II activity. We found that the replacement of the etoposide carbohydrate moiety with a metallocenyl group led to organometallic conjugates exhibiting differentiated antiproliferative activity. Biological studies demonstrated that two ferrocenylalkylamino conjugates were notably more active than etoposide, with submicromolar or low-micromolar IC₅₀ values towards SW620, etoposide-resistant SW620E, and methotrexate-resistant SW620M cancer cell lines. Moreover, the simplest ferrocenylmethylamino conjugate exerted dual inhibitory action against tubulin polymerization and topoisomerase II activity while other studied compounds affected only topoisomerase II activity.

Biotin-phenosafranin as a new photosensitive conjugate for targeted therapy and imaging

A biotinylated phenazine compound as a phenosafranin conjugate (Biot-PSF) was synthesized and reported for the first time.

Pyrazoles: 'one-pot' synthesis from arenes and carboxylic acids

A rapid and efficient method for 'one-pot' synthesis of pyrazoles from (hetero)arenes and carboxylic acids via successive formation of ketones and β-diketones followed by heterocyclization with hydrazine has been developed. The utility of the RCOOH/TfOH/TFAA acylation system for intermediate production of ketones and 1,3-diketones is a key feature of this approach. The preliminary evaluation of the anticancer activity of the synthesized pyrazoles is performed.

Quantum Dot Based Fluorescent Traffic Light Nanoprobe for Specific Imaging of Avidin-Type Biotin Receptor and Differentiation of Cancer Cells

Sensitive and specific visualization of cell surface biotin receptors (BRs) a class of clinically important biomarkers, remains a challenge. In this work, a dual-emission ratiometric fluorescent nanoprobe is developed for specific imaging of cell surface avidin, a subtype of BRs. The nanoprobe comprises a dual-emission quantum dot nanohybrid, wherein a silica-encapsulated red-emitting QD (rQD@SiO₂) is used as the "core" and green-emitting QDs (gQDs) are used as "satellites", which are further decorated with a new "love-hate"-type BR ligand, a phenanthroline-biotin conjugate with an amino linker. The nanoprobe shows intense rQD emission but quenched gQD emission by the BR ligand. Upon imaging, the rQD emission stays constant and the gQD emission is restored as cell surface avidin accrues. Accordingly, the overlaid fluorescence color collected from red and green emission changes from red to yellow and then to green. We refer to such a color change as a traffic light pattern and the nanoprobe as a fluorescent traffic light nanoprobe. We demonstrate the application of our fluorescent traffic light nanoprobe to characterize cancer cells. By the traffic light pattern, cervical carcinoma and normal cells, as well as different-type cancer cells including BR-negative colon cancer cells, BR-positive hepatoma carcinoma cells, breast cancer cells, and their subtypes, have been visually differentiated. We further demonstrate a use of our nanoprobe to distinguish the G2 phase from other stages in a cell cycle. These applications provide new insights into visualizing cell surface biomarkers with remarkable imaging resolution and accuracy.

Structural Characterization of the Avidin Interactions with Fluorescent Pyrene-Conjugates: 1-Biotinylpyrene and 1-Desthiobiotinylpyrene

Avidin is a tetrameric protein that belongs to the calycin superfamily. It has been studied mainly because of its extraordinary affinity to biotin, which led to a wide range of applications based on the avidin-biotin system. In the present study, we report the first crystal structures of avidin in a complex with two novel fluorescent pyrene derivatives: 1-biotinylpyrene (B9P) and 1-desthiobiotinylpyrene (D9P). The crystal structures were solved by molecular replacement using the coordinates of avidin molecule as a starting model and the final models of avidin/B9P and avidin/D9P were refined to resolutions of 2.0 Å and 2.1 Å, respectively. Our data reveal changes in loop conformation as well as in overall fold and quaternary arrangement of the avidin upon the binding of these fluorescent probes. Moreover, the crystal structures allowed analysis of the details of the interactions between the protein and the pyrene derivatives. Structural description of the complexes will contribute to the design of conjugates for expanding the capabilities of avidin–biotin technology.

Achievement of linear response for competitive bioaffinity assays of ligands: criteria of optimized interaction systems

For a linear response, an optimized competitive bioaffinity assay of a ligand requiresC_RT> 3 ×C_PT,C_PT> 50 ×K_dR, andK_dR> 260 ×K_dX(C_RTandC_PTare concentrations of the probe and protein whileK_dXandK_dRareK_dfor the ligand and probe, respectively).

(CF3CO)2O/CF3SO3H-mediated synthesis of 1,3-diketones from carboxylic acids and aromatic ketones

A very simple and convenient reaction for 1,3-diketone preparation from carboxylic acids and aromatic ketones in TFAA/TfOH system is described. When the β-phenylpropionic acids were used as starting materials, they initially gave 1-indanones and then underwent further acylation with the formation of 2-(β-phenylpropionyl)-1-indanones as the main reaction products. In addition, the application of the proposed protocol allowed for the synthesis of selected polysubstituted pyrazoles in a one-pot procedure directly from acids and ketones.

Structural investigation of the interactions of biotinylruthenocene with avidin

The crystal structure of avidin, a protein from hen egg white, was determined in the form of a complex with biotinylruthenocene. This biotin-derived organometallic ligand is a potential anticancer agent for targeted therapy based upon avidin-biotin technology. Isothermal titration calorimetry experiments, involving avidin complexes with biotin (vitamin H or B7) derivatives, show differences in their affinity to the protein in comparison to its avidin-biotin complex, the strongest known biochemical interaction in Nature. The crystal structure of the first complex of avidin with biotinylruthenocene, determined at 2.5Å resolution (PDB: 4I60), shows unique interactions of the ruthenocene moiety with avidin. Biotin derivatives exhibit weaker affinity to avidin then biotin, which allows their wider use in biotechnology. The specific properties of biotinylruthenocene and the knowledge of its interactions with avidin may be useful in biochemical, medical, and nanotechnological applications.