Reduced Molecular Flavins as Single-Electron Reductants after Photo-Excitation

Flavoenzymes mediate a multitude of chemical reactions and are catalytically active both in different oxidation states and in covalent adducts with reagents. The transfer of such reactivity to the organic laboratory using simplified molecular flavins is highly desirable and such applications in (photo-)oxidation reactions are already established. However, molecular flavins have not been used for the reduction of organic substrates yet, although this activity is known and well-studied for DNA photolyase enzymes. We report a catalytic method using reduced, molecular flavins as photo-reductants and γ-terpinene as sacrificial reductant. Additionally, we present our design for air-stable, reduced flavin catalysts, which is based on a conformational bias strategy and circumvents the otherwise rapid reduction of O2 from air. Using our catalytic strategy, we were able to replace super-stoichiometric amounts of the rare-earth reductant SmI2 in a 5-exo-trig cyclization of substituted barbituric acid derivatives. Such flavin-catalyzed reductions are anticipated to be of broad applicability and their straightforward synthesis indicates future use in stereo- as well as site-selective transformations.

Comparative Effects of Solvents on the Herbal Extraction of Antidiabetic Phytochemicals

Aims: The study determined and compared the herbal extraction yields using water, ethanol and hydromethanol solvent and the solvent extracting the highest antidiabetic constituents. Place: The study took place in the Department of Chemistry (Organic Laboratory), Federal University of Technology Owerri, Nigeria. Methodology: The antidiabetic contents of Moringa oleifera (Moringa) and Vernonia amygdalina (bitter leaf) were extracted by soaking using water, ethanol and hydromethanol (1:1) as solvents. The phytochemicals analysis was done both qualitatively and quantitatively (using Spectrophotometer (UV-V15)). Data collected were statistically analysed using SPSS version 10 tools. Results: The crude ethanolic extraction was found to give the highest extract yield of 46.06% and 38.91% from Moringa and bitter leaf, respectively. There were more phytochemicals obtained from Moringa (28+) than from Vernonia crude extracts (21+). The antidiabetic phytochemicals identified in both plants included Steroids, Phenols, Cardiac glycosides and Terpenoids. Ethanol extracted the Glycosides, Terpenoids and Phenols in relative abundance.. Hydromethanol solvent extraction yielded the highest concentrations of Steroids from Moringa (59.87mg/100g) and bitter leaves (75.43mg/100g) as well as highest extraction of Cardiac glycosides from both plants. Water extracted the highest concentrations of Phenols from both Moringa (0.32mg/g); bitter leaf (0.25mg/g) and Terpenoids from Moringa. Conclusion: This study suggests that the choice of solvent (s) for phytochemical extraction (s) should consider factors such as the plant material (s) and the phytochemical (s) involved. So, Water > Hydromethanol > ethanol could be used for extracting phytochemicals for diabetes therapy.

Molecular Editing of Flavins for Catalysis

The diverse activity of flavoenzymes in organic transformations has fascinated researchers for a long time. However, when applied outside an enzyme environment, the isolated flavin cofactor only shows largely reduced activity. This highlights the importance of embedding the reactive flavin’s isoalloxazine core in defined surroundings. The latter include crucial non-covalent interactions with amino acid side chains or backbone as well as controlled access to reactants such as molecular oxygen. Nevertheless, molecular flavins are increasingly applied in the organic laboratory as valuable organocatalysts. Chemical modification of the parent isoalloxazine structure is of particular interest in this context in order to achieve reactivity and selectivity in transformations, which are so far only known with flavoenzymes or even unprecedented. This review aims to give a systematic overview of the reported designed flavin catalysts and highlights the impact of each structural alteration. It is intended to serve as a source of information when comparing the performance of known catalysts, but also when designing new flavins. Over the last decades, molecular flavin catalysis has emerged from proof-of-concept reactions to increasingly sophisticated transformations. This stimulates anticipating new flavin catalyst designs for solving contemporary challenges in organic synthesis.

Simple and efficient in situ generated copper nanocatalyst for stereoselective semihydrogenation of alkynes

Development of a simple, effective, and practical method for (Z)-selective semihydrogenation of alkynes have been considered necessary for easy-to-access applications in organic laboratory scales. Herein, (Z)-selective semihydrogenation of alkynes was...

Beyond the beaker: students’ use of a scaffold to connect observations with the particle level in the organic chemistry laboratory

Understanding ongoing chemical processes in the laboratory requires constant shifting between different representational levels—the macroscopic, submicroscopic, and symbolic levels—and analysis of the various mechanistic features of each of these levels. Thus, the ability to explain observations of chemical phenomena with regard to their submicroscopic levels in the laboratory is a key requirement. Research shows that students have difficulty in discerning and comprehending the meaning and visualization of the submicroscopic level. Traditional laboratory instruction often fails to help students discern the relationship between their observations and the corresponding chemical processes. Consequently, there is a high demand for new teaching strategies which address these issues. Therefore, we developed and implemented a scaffold for the organic laboratory and tested it in a research study using qualitative methods. The scaffold encourages students to purposefully separate and connect the macroscopic and submicroscopic representational levels. The implementation of the scaffold was accompanied by semi-structured pre- and post-interviews with students (N = 22) and an analysis of students’ work with the scaffold in the laboratory. We analysed students’ sense-making approach while reflecting on organic syntheses before and after working with the scaffold, and characterized changes in their approach. The findings emphasize the need to develop further resources to support students’ understanding of the submicroscopic level. Implications of these findings for research and teaching to foster meaningful learning in the organic laboratory are discussed.