An efficient conversion of berberine into a rhoeadine via an indenobenzazepine

Treatment of ketoaziridine $\text{4}$ with aqueous formaldehyde gives the unusual bridged indenobenzazepine derivative $\text{6}$ whose reduction uith sodium cyanoborohydride produces trans ketol $\text{8}$. In the presence of hydrochloric acid, $\text{8}$ undergoes irreversible conversion to the more stable cis ketol $\text{10}$. Periodate oxidation of $\text{8}$ supplies γ-laotone $\text{11}$. NaBH₄ reduction of $\text{11}$ followed by acid treatment affords δ-lactone $\text{12}$ which upon reduction and O-methylation furnishes cis rhoeadine analog $\text{14}$.     

Improved Nafion-based amperometric sensor for hydrogen in argon

An improved polymer electrolyte membrane fuel cell-based amperometric hydrogen sensor has been developed. The sensor operates at room temperature, and the electrolyte used in the sensor is Nafion which is a proton-conducting solid polymer electrolyte. Platinum black is used as both anode and cathode. The sensor functions as a fuel cell, H₂/Pt//Nafion//Pt/O₂, and a mechanical barrier limits the supply of hydrogen to the sensing side electrode. The limiting current is found to be linearly related to the hydrogen concentration. The sensor can be used to measure hydrogen in argon in parts per million and percentage levels. The basic principle, details of assembly, and response behavior of the sensor are discussed.     

A Cobalt(I) Pincer Complex with an η2‐Caryl−H Agostic Bond: Facile C−H Bond Cleavage through Deprotonation,Radical Abstraction,and Oxidative Addition

The synthesis and reactivity of a Co^I pincer complex [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ featuring an η²‐ C_aryl−H agostic bond is described. This complex was obtained by protonation of the Co^I complex [Co(PCP^NMe‐iPr)(CO)₂]. The Co^III hydride complex [Co(PCP^NMe‐iPr)(CNtBu)₂(H)]⁺ was obtained upon protonation of [Co(PCP^NMe‐iPr)(CNtBu)₂]. Three ways to cleave the agostic C−H bond are presented. First, owing to the acidity of the agostic proton, treatment with pyridine results in facile deprotonation (C−H bond cleavage) and reformation of [Co(PCP^NMe‐iPr)(CO)₂]. Second, C−H bond cleavage is achieved upon exposure of [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ to oxygen or TEMPO to yield the paramagnetic Co^II PCP complex [Co(PCP^NMe‐iPr)(CO)₂]⁺. Finally, replacement of one CO ligand in [Co(ϰ³P,CH,P‐P(CH)P^NMe‐iPr)(CO)₂]⁺ by CNtBu promotes the rapid oxidative addition of the agostic η²‐C_aryl−H bond to give two isomeric hydride complexes of the type [Co(PCP^NMe‐iPr)(CNtBu)(CO)(H)]⁺.     

Novel 7‐Nitro‐1‐(Piperidin‐4‐yl)‐4,5‐Dihydro‐[1,2,4] Triazolo[4,3‐a]Quinoline‐Sulphonamide Derivatives as Antimicrobial Agents: Design,Synthesis, and Bio‐Activity

In attempt to search for more potent antimicrobial agents, a series of 7‐nitro‐1‐(piperidin‐4‐yl)‐4,5‐dihydro‐[1,2,4]triazolo[4,3‐a]quinoline‐derived sulphonamides were synthesized. Their structures were established by elemental analyses, IR, and NMR (¹H and ¹³C) spectral data. The antibacterial activity of the obtained compounds was investigated against different Gram‐negative (Escherichia coli and Pseudomonas aeruginosa) and Gram‐positive (Bacillus subtilis and Staphylococcus aureus) bacteria and antifungal activity against two fungal strains (Aspergillus niger and Aspergillus clavatus) using disk diffusion method at various concentrations (20, 40, 60, and 80 μg/mL). The study reveals that most of the title compounds showed significant antibacterial and fungal activity when compared with their respective standards streptomycin and griseofulvin.     

A Simple and Efficient Approach for Estimating Recovery of a Preparative Reversed Phase HPLC Purification

The widely applied reversed phase high-performance liquid chromatography (RP-HPLC) is an indispensable purification technique in drug discovery. During drug discovery, recovery was usually calculated based on the weight of the purified product after drying over the weight of the crude material multiplied by the assumed purity from HPLC/UV area percent of the product. Such a purity assumption can be off significantly when the crude material contains water, solvents, other UV-inactive impurities and inorganic salts. In this paper, we report a simple and efficient way to estimate recovery of preparative HPLC purification process. It is based on the ratio of the HPLC/UV peak area measured for the product in the crude solution and that in the final collected fraction with both accounted for their volumes. This approach eliminates not only the need for drying of the collected fraction to calculate recovery but also the inaccuracy associated with the true content in the crude sample using the traditional method. A systematic study was conducted to verify this method using caffeine mixed with various UV-active and -inactive impurities. The calculated recoveries using this approach were found to be consistent within 4% with the true recoveries based on dry weight estimation. The approach has been successfully applied for our in-house purifications. Furthermore, the approach was extended to library purifications, where in many cases heart-cutting the desired peaks is used to meet the purity requirements.

     

Enzyme–Carbon Nanotube Conjugates in Room-temperature Ionic Liquids

Room-temperature ionic liquids (RTILs) are intriguing solvents, which are recognized as “green” alternatives to volatile organics. Although RTILs are nonvolatile and can dissolve a wide range of charged, polar, and nonpolar organic and inorganic molecules, there remain substantial challenges in their use, not the least of which is the solvents’ high viscosity that leads to potential mass transfer limitations. In the course of this work, we discovered that the simple adsorption of the bacterial protease, proteinase K, onto single-walled carbon nanotubes (SWNTs) results in intrinsically high catalytic turnover. The high surface area and the nanoscopic dimensions of SWNTs offered high enzyme loading and low mass transfer resistance. Furthermore, the enzyme–SWNT conjugates displayed enhanced thermal stability in RTILs over the native suspended enzyme counterpart and allowed facile reuse. These enzyme–SWNT conjugates may therefore provide a way to overcome key operational limitations of RTIL systems.     

BIFC and QFC promoted rapid and cleaner aromatization of 1,4‐dihydropyridines under solvent‐free condition

This communication expresses aromatisation of 1,4‐dihydropyridines to pyridine derivatives with the help of alumina supported benzimidazolium fluorochromate (BIFC) and quinolinium fluorochromate (QFC) as oxidants under solvent‐free microwave irradiation. Moderate to excellent yield (80‐98%) of pyridine derivatives were achieved by this methodology.