Cristina E. A. Sousa

Food adulteration is a widespread global issue threatening consumer health and food safety.

The spread of point-of-care (PoC) glucose sensor technologies is crucial for effective diabetes management. In this context, we present a novel electrochemical biosensing platform that integrates various carbon allotropes—biographene (BGr), zinc oxide (ZnO)–modified multi-walled carbon nanotubes (MWCNT-ZnO), and biologically derived carbon dots (CDs)—in a polyaniline-based matrix (PANI) for glucose detection. The sensing layer was prepared by electropolymerizing aniline in the presence of the individual carbon allotropes and the enzyme glucose oxidase (GOx) on the surface of a screen-printed gold electrode (Au-SPE). The analytical performance of the sensor was evaluated by chronoamperometry (CA) in phosphate-buffered saline (PBS) and glucose-spiked human serum. The morphology and chemical composition of the carbon allotropes were characterized by using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Among the sensors tested, the carbon dot (CD)–based sensor demonstrated the best analytical performance, with a limit of detection (LOD) of 1.08 mmol/L and a sensitivity of 0.453 μA per decade of glucose concentration. This covers a linear working range of 1.56 to 75.0 mmol/L, which includes the typical physiological glucose concentration range observed in both healthy individuals and individuals with diabetes. This study aims to improve enzymatic glucose biosensors using fructose-derived carbon dots and PANI to enhance enzyme immobilization, electron transfer, and sensitivity while maintaining low cost and sustainability, offering strong potential for applications in personalized health monitoring and long-term chronic disease management.

This review provides a fresh overview of non-canonical amino acids and their applications in the design of peptidomimetics. Non-canonical amino acids appear widely distributed in nature and are known to enhance the stability of specific secondary structures and/or biological function. Contrary to the ubiquitous DNA-encoded amino acids, the structure and function of these residues are not fully understood. Here, results from experimental and molecular modelling approaches are gathered to classify several classes of non-canonical amino acids according to their ability to induce specific secondary structures yielding different biological functions and improved stability. Regarding side-chain modifications, symmetrical and asymmetrical α,α-dialkyl glycines, Cα to Cα cyclized amino acids, proline analogues, β-substituted amino acids, and α,β-dehydro amino acids are some of the non-canonical representatives addressed. Backbone modifications were also examined, especially those that result in retro-inverso peptidomimetics and depsipeptides. All this knowledge has an important application in the field of peptidomimetics, which is in continuous progress and promises to deliver new biologically active molecules and new materials in the near future.

Given the pandemic situation, there is an urgent need for an accurate test to monitor antibodies anti-SARS-CoV-2, providing crucial epidemiological and clinical information to monitor the evolution of coronavirus disease in 2019 (COVID-19) and to stratify the immunized and asymptomatic population. Therefore, this paper describes a new cellulose-based test strip for rapid and cost-effective quantitative detection of antibodies to SARS-CoV2 virus by colorimetric transduction. For this purpose, Whatman paper was chemically modified with sodium metaperiodate to introduce aldehyde groups on its surface. Subsequently, the spike protein of the virus is covalently bound by forming an imine group. The chemical control of cellulose paper modification was evaluated by Fourier transform infrared spectroscopy, thermogravimetry and contact angle analysis. Colorimetric detection of the antibodies was performed by a conventional staining method using Ponceau S solution as the dye. Color analysis was performed after image acquisition with a smartphone using Image J software. The color intensity varied linearly with the logarithm of the anti-S concentration (from 10 ng/mL to 1 μg/mL) in 500-fold diluted serum samples when plotted against the green coordinate extracted from digital images. The test strip was selective in the presence of nucleocapsid antibodies, urea, glucose, and bovine serum albumin with less than 15% interference, and detection of antibodies in human serum was successfully performed. Overall, this is a simple and affordable design that can be readily used for mass population screening and does not require sophisticated equipment or qualified personnel.

A five-step synthesis of (S)-7-hydroxy-5-aza-8a-epi-d-swainsonine [(3S,4S,4aS,5S,6R)-octahydropyrrolo[1,2-b]pyridazine-3,4,5,6-tetraol] was accessed in good overall yield from readily available d-erythrosyl benzylidene acetal buta-1,3-diene. The key step of the reaction sequence is a full stereoselective Diels–Alder cycloaddition between­ the diene and dienophile: diethyl azodicarboxylate (DEAD) or di-tert-butyl azodicarboxylate (DBAD). The cycloadducts were further transformed into the title 5-aza-indolizidine. Optimized procedures were obtained for the synthesis of intermediates and products.

D-Erythrosyl aziridines were obtained from d-erythrosyl triazoles either by photolysis or through diazirine intermediates. These were found to undergo rich, high yielding chemistry by reaction with protic acids (HCl, BiI₃/H₂O and trifluoroacetic acid) leading to two types of furanoid sugar α-amino acids, and polyhydroxylprolines. Based on experimental evidence, reaction mechanisms have been proposed for the syntheses.

This is the first synthetic report of (3S,4R)-dihydroxy-N-alkyl-L-homoprolines described so far. 2,4-O-Benzylidene-D-erythrose was obtained from D-glucose with an improved yield, and then transformed into the title (3S,4R)-dihydroxy-N-alkyl-L-homoprolines, in a two-step strategy, with excellent overall yields. Hydrogenolysis of the benzyl group led to the NH congener. The synthesis of final products from 1,4-lactone intermediates was studied by computational means either under acidic or basic conditions. The theoretical mechanism studies fully explain the experimental results: (a) an equilibrium between L-homoprolines and their bicyclic counterparts is established in acids; (b) the equilibrium suffers a complete displacement towards the L-homoproline side in a basic medium.

Lactones are important biological molecules that offer a new molecular scaffold to develop new and more selective inhibitors targeting glycosidases [1]. The chemical routes that can speed up their synthesis in a stereo- and regio-selective way have become a major demand. A new derivative of 2,4-O-alkylidene-D-erythrose, enclosing a C=C moiety into a 1,5-lactone ring, was found to induce a complete facial selectivity in 1,3-dipolar cycloadditions [2]. This new D-erythrosyl 1,5-lactone was studied as a Michael acceptor with sulfur and nitrogen nucleophiles and from which a complete facial selectivity was demonstrated in all reactions [3]. Sulfides attack exclusively at C-4, but primary amines and hydrazine attack both at C-2 and C-4. The sulfur adducts formed are 1 (D-erythrose derivative):1 (nucleophile), and the nitrogen adducts are 1:2. The theoretical and computational results clearly explain the origin of the stereo-selectivity, and the energetic course of the reactions, starting with nitrogen and sulfide nucleophiles. Considering that the 1,4-lactones obtained in this work offer a new molecular scaffold for organic synthesis, these new results provide a solid theoretical platform that can be used to speed up synthesis of other derivatives in a stereo- and regio-selective way. References [1]Rocha, J. F.; Cerqueira, N. M. F. S. A. Glucosidases and galactosidases as drug targets. Curr. Top. Biochem. Res. 2017, 18, 117− 126. [2]Sousa, C. E.; Ribeiro, A. M.; Gil Fortes, A.; Cerqueira, N. M.; Alves, M. J. Total Facial Discrimination of 1,3-Dipolar Cycloadditions in a d-Erythrose 1,3-Dioxane Template: Computational Studies of a Concerted Mechanism. J. Org. Chem. 2017, 82 (2), 982−991. [3]Rocha, J. F.; Freitas, D. S.; Noro, J.; Teixeira, C. S. S.; Sousa, C. E.; Alves, M. J.; Cerqueira, N. M. F. S. A. Total Stereoselective Michael Addition of N- and S- Nucleophiles to a d-Erythrosyl 1,5-Lactone Derivative. Experimental and Theoretical Studies Devoted to the Synthesis of 2,6-Dideoxy-4-functionalized-d-ribono-hexono-1,4-lactone. J. Org. Chem. 2018, 83 (15), 8011-8019 DOI: 10.1021/acs.joc.8b00769.