Abstract: (-)-Menthol is one of the most in-demand monoterpenoids, as it is used in the pharmaceutical, cosmetics, fragrance, and food industries. Traditionally isolated from mint oils, it is nowadays produced synthetically using menthone, citronellal, geraniol, myrcene, or m-cresol as precursors. The synthesis of optically pure menthol, which is highly demanded in the industry, involves either enantioselective resolution or asymmetric catalysis. This review covers the literature of the last two decades on the copper-catalyzed synthesis of menthol and provides an in-depth analysis of the most promising methods. These methods involve either homogeneous or heterogeneous catalysis, efficiently use readily available and inexpensive Cu salts, and give access to (-)-menthol in high yields under mild reaction conditions. In many cases, copper-catalyzed reactions allow sustainable and high-yielding synthesis of (-)-menthol. For instance, the hydrogenation of citronellal to (-)-menthol was achieved in 98.6% yield in 30.5 h using a Cu/SiO2 catalyst. The hydrogenation of (-)-menthone to (-)-menthol catalyzed by Cu/Al2O3 proceeds with 99% conversion and selectivity within 0.7 h. Notably, copper sepiolite-catalyzed hydrogenation of citral to (-)-menthol was completed in 100% yield. The review discusses the effect of the catalyst composition, the oxidation state of copper, the type of inert support, temperature, pressure, and the choice of solvents and hydrogen sources on the yield and selectivity of the reaction. The review also compares different approaches to Cu-catalyzed synthesis of (-)-menthol and discusses future perspectives in sustainable catalytic synthesis. In addition, it gives a comprehensive overview of state-of-the-art methods that allow the industry to produce high-purity (-)-menthol cost-effectively.
Following publication of the article entitled “Progress of the Chemical Composition and Pharmacological Activities of Podocarpus nagi’’[1], the DOIs of references 54 and 59 were incomplete. This has now been corrected. This correction is limited to the references' DOIs and has no impact on the scientific content, results, discussion, or conclusions of the article. Details of the error and the correction are provided below. Original: [54] Chen, L.B.; Wang, J.H.; Zang, J.; Hu, S.Y.; Zhu, X.Y. Study on β- elemene induced apoptosis of mouse melanoma B16 cells. Bulletin of Jinling Hospital, 1999, 12(1), 48-49. http://dx.doi.org/10.16571.j.cnki.1008-8199.1999.01.018 [59] Ruan, N.; Shi, Z. Observation of the therapeutic effect of intraperitoneal retention of elemene emulsion on the prevention and treatment of gastrointestinal tumor cavity metastasis. Fujian Med. J., 1997, 19(2), 34-35. http://dx.doi.org/10.20148.j.fmj.1997.02.076 Corrected: [54] Chen, L.B.; Wang, J.H.; Zang, J.; Hu, S.Y.; Zhu, X.Y. Study on β- elemene induced apoptosis of mouse melanoma B16 cells. Bulletin of Jinling Hospital, 1999, 12(1), 48-49. http://dx.doi.org/10.16571/j.cnki.1008-8199.1999.01.018 [59] Ruan, N.; Shi, Z. Observation of the therapeutic effect of intraperitoneal retention of elemene emulsion on the prevention and treatment of gastrointestinal tumor cavity metastasis. Fujian Med. J., 1997, 19(2), 34-35. http://dx.doi.org/10.20148/j.fmj.1997.02.076 The original article has been updated accordingly. This corrigendum is published to ensure transparency and accuracy of the scholarly record. The corrected version of the article is available online at: https://www.eurekaselect.com/article/152500 The authors regret these errors and apologise for any inconvenience they may have caused.
RGD peptides are a class of bioactive short peptides defined by the conserved arginine-glycine-aspartic acid tripeptide motif. This core sequence can specifically recognize and tightly bind to overexpressed integrin receptors on the surfaces of various cell membranes, effectively mediating dynamic cell-extracellular matrix crosstalk and modulating multiple vital cellular physiological processes such as adhesion, migration, proliferation, and angiogenesis, which endows RGD peptides with remarkably broad and promising biomedical application prospects. In this review, the latest research progress surrounding RGD peptides is systematically summarized, covering their structural classification, rational chemical modification strategies to enhance binding affinity and in vivo stability, and their versatile biomedical applications. Their practical uses in direct targeted therapeutic intervention, multifunctional targeted drug delivery, non-invasive molecular imaging, integrated imaging-guided theranostics, and regenerative tissue engineering are thoroughly elaborated. Moreover, the major bottlenecks and core challenges that hinder the clinical transformation of RGD-derived biomaterials are analyzed in depth, and feasible, targeted research directions for subsequent exploration are proposed. This comprehensive review is expected to offer valuable theoretical references for the rational structural optimization, performance improvement, and further clinical translation of RGD peptide-based therapeutic agents and functional biomaterials.
Abstract: Coumarin and chromene derivatives are important oxygen-containing heterocyclic frameworks with diverse applications in medicinal chemistry, pharmaceuticals, and functional materials. In this review, microwave-assisted synthetic routes to coumarin and chromene derivatives are critically evaluated in terms of catalyst, microwave conditions, reaction time, yield, sustainability, and catalyst recycling. The literature was systematically classified according to the target scaffolds and major synthetic transformations, and the methods were compared in terms of efficiency and green chemistry aspects. Coumarins are mainly synthesized via Pechmann and Knoevenagel reactions, whereas chromenes are accessed through Knoevenagel/Michael addition-cyclization, multicomponent, annulation, cascade, cyclization, and cycloaddition reactions. Several methods employ solvent-free or aqueous media, heterogeneous and recyclable catalysts, nanocatalysts, ionic liquids, or catalyst-free conditions. Key limitations include restricted microwave penetration and heating uniformity at larger scales, pressure build-up in closed vessels, dependence on the dielectric properties of solvents, difficulties in catalyst preparation, product losses during isolation, and safety concerns associated with hazardous solvents and reagents. A comparative assessment of atom economy, reaction mass efficiency, process mass intensity, E-factor, and energy consumption is limited by inconsistent process reporting. Future research should emphasize continuous-flow microwave reactors, scale-up validation, standardized energy reporting, life-cycle assessment of catalysts and solvents, leaching studies, instrument-to-instrument reproducibility, and comparison with conventional thermal, ultrasound, photochemical, and mechanochemical methods. Overall, microwave irradiation is an effective process-intensification technique for the synthesis of coumarins and chromenes, particularly for shortening reaction times and achieving efficient catalytic conversions with reduced solvent use.
Abstract: Fluorinated compounds are essential in modern chemistry, especially in drug design, where fluorine enhances metabolic stability and lipophilicity, enabling the development of more effective therapeutics with improved pharmacological properties. The presence of a fluorine atom in an organic molecule gives rise to observable 13C-19F coupling in 13C{1H} NMR spectroscopy, offering valuable structural insight. The magnitude of the coupling constant (JCF) varies significantly and leads to characteristic splitting of 13C-signals, although the precise contribution of individual factors is often complex and not easily delineated. This review surveys the variations in 13C-19F coupling constants across fluorinated bioactive compounds, highlighting the different types and ranges of observed JCF values and their corresponding 13C NMR splitting patterns. The coupling constants are generally influenced by structural, electronic, and external factors such as solvent and temperature, although the precise contribution of individual parameters is often difficult to define. A total of 45 different types of reported fluorinated molecules have been screened as targeted case studies, and these are highlighted along with their respective JCF data, presented in tabular form, and carbon signals assigned based on coupling constants. By comparing trends across various structural classes, this review provides a comprehensive understanding of 13C-19F couplings, serving as a practical guide for the rational design and optimization of fluorine-containing molecules.
