Direct and Metal-Catalyzed Photochemical Dimerization of the Phthalide (Z)-Ligustilide Leading to Both [2 + 2] and [4 + 2] Cycloadducts: Application to Total Syntheses of Tokinolides A–C and Riligustilide

Discovery of a Potent Antiosteoporotic Drug Molecular Scaffold Derived from Angelica sinensis and Its Bioinspired Total Synthesis

Angelica sinensis, commonly known as Dong Quai in Europe and America and as Dang-gui in China, is a medicinal plant widely utilized for the prevention and treatment of osteoporosis. In this study, we report the discovery of a new category of phthalide from Angelica sinensis, namely falcarinphthalides A and B (1 and 2), which contains two fragments, (3R,8S)-falcarindiol (3) and (Z)-ligustilide (4). Falcarinphthalides A and B (1 and 2) represent two unprecedented carbon skeletons of phthalide in natural products, and their antiosteoporotic activities were evaluated. The structures of 1 and 2, including their absolute configurations, were established using extensive analysis of NMR spectra, chemical derivatization, and ECD/VCD calculations. Based on LC-HR-ESI-MS analysis and DFT calculations, a production mechanism for 1 and 2 involving enzyme-catalyzed Diels-Alder/retro-Diels-Alder reactions was proposed. Falcarinphthalide A (1), the most promising lead compound, exhibits potent in vitro antiosteoporotic activity by inhibiting NF-κB and c-Fos signaling-mediated osteoclastogenesis. Moreover, the bioinspired gram-scale total synthesis of 1, guided by intensive DFT study, has paved the way for further biological investigation. The discovery and gram-scale total synthesis of falcarinphthalide A (1) provide a compelling lead compound and a novel molecular scaffold for treating osteoporosis and other metabolic bone diseases.

Novel ligustilide derivatives target quorum sensing system LasR/LasB and relieve inflammatory response against Pseudomonas aeruginosa infection

The increasing antibiotic resistance driven by Pseudomonas aeruginosa typically leads to uncontrolled and persistent inflammatory damage, which is primarily attributed to the virulence and biofilms produced by the bacteria. Herein, we present a novel anti-infective drug strategy designed to inhibit the bacterial quorum sensing system, thereby attenuating P. aeruginosa virulence, and modulating inflammation from drug-resistant bacterial infections. We discovered new quorum sensing LasR/LasB inhibitors derived from the structural modification of a ligustilide derivative library. Of these compounds, 5f demonstrated significant inhibitory activity against LasB (LasB-gfp, IC50 = 8.7 μM) and a moderate inhibitory effect on P. aeruginosa biofilms (IC50 = 7.4 μM). Through live image analysis in a fluorescent protein-labeled zebrafish larva model, we observed that compound 5f significantly inhibited the migration of macrophages. Moreover, compound 5f effectively attenuated quorum sensing-mediated virulence factors and biofilm formation by P. aeruginosa. It also alleviated the inflammatory response by P. aeruginosa-infected macrophages through the downregulation of mitogen-activated protein kinase and NF-κB signal-transduction pathways. Notably, in vivo experiments, this compound demonstrated marked therapeutic effects in acute lung injury models induced by lipopolysaccharides from P. aeruginosa. These results indicate that compound 5f has the potential to be a novel anti-infective candidate against drug-resistant infections caused by P. aeruginosa.

[2 + 2]-Cycloaddition-derived cyclobutane natural products: structural diversity, sources, bioactivities, and biomimetic syntheses

This review summarizes the structural diversity, bioactivities, and biomimetic synthesis of [2 + 2]-type cyclobutane natural products, along with discussion of their biosynthesis, stereochemical analysis, racemic occurrence, and biomimetic synthesis.

Total Syntheses of the Structures Assigned to the Marine Natural Products Orthoscuticellines A-E

The readily prepared and vinylated β-carboline 11 has been converted over one or two steps into compounds 1-5, the structures assigned to the recently reported marine natural products orthoscuticellines A-E. The spectral data recorded on the synthetically derived compounds are fully consistent with the assigned structures and, on making allowances for variations in the pH of the medium in which the spectra of the natural products were recorded, it is concluded that the structures assigned to orthoscuticellines A-E are most likely correct. Certainly, the calculated ¹³C NMR spectra of the α-, γ-, and δ-carboline isomers of compounds 1-5 suggest that orthoscuticellines A-E do incorporate the assigned β-carboline core.

Construction of 3,12-Diazatetracyclododecane-dienes through Unexpected Visible-Light-Induced Radical Cascade Cyclization

A novel visible-light-induced cascade radical cyclization reaction of 3-cyano-4-aryl-1,4-dihydropyridines for the construction of 3,12-diazatetracyclododecane-diene derivatives is reported for the first time. In the presence of 410 nm blue LED lamp as the light source and ethanol as the solvent, the reactions proceed smoothly to afford photocyclization products in good yields. The process is carried out through the breaking of original C═C double bonds and the formation of three new single bonds in one pot and proved to be able to tolerate different substituents.

Photochemical synthesis of 3-hydroxyphenanthro[9,10-c]furan-1(3H)-ones from α-keto acids and alkynes

A novel and efficient method for the synthesis of 3-hydroxyphenanthro[9,10-c]furan-1(3H)-ones has been achieved from α-keto acids and alkynes through photo-initiated transformation, providing a range of products in good to excellent yields.

Improving natural product research translation: From source to clinical trial

While great interest in health effects of natural product (NP) including dietary supplements and foods persists, promising preclinical NP research is not consistently translating into actionable clinical trial (CT) outcomes. Generally considered the gold standard for assessing safety and efficacy, CTs, especially phase III CTs, are costly and require rigorous planning to optimize the value of the information obtained. More effective bridging from NP research to CT was the goal of a September, 2018 transdisciplinary workshop. Participants emphasized that replicability and likelihood of successful translation depend on rigor in experimental design, interpretation, and reporting across the continuum of NP research. Discussions spanned good practices for NP characterization and quality control; use and interpretation of models (computational through in vivo) with strong clinical predictive validity; controls for experimental artefacts, especially for in vitro interrogation of bioactivity and mechanisms of action; rigorous assessment and interpretation of prior research; transparency in all reporting; and prioritization of research questions. Natural product clinical trials prioritized based on rigorous, convergent supporting data and current public health needs are most likely to be informative and ultimately affect public health. Thoughtful, coordinated implementation of these practices should enhance the knowledge gained from future NP research.

Studying Mass Balance and the Stability of (Z)-Ligustilide from Angelica sinensis Helps to Bridge a Botanical Instability-Bioactivity Chasm

Numerous reports assigning (Z)-ligustilide (1) the role of a major bioactive principle in Apiaceae botanicals are called into question by the recurrent demonstrations of 1 being an unstable, rapidly degrading compound, ultimately leading to dynamic residual complexity. While Angelica sinensis is recognized for its therapeutic value in (peri-)menopausal symptom management, its purported active principle, 1, represents a typical example of the instability-bioactivity chasm of botanicals. To help bridge the gap, this study used both the essential oil and purified 1 obtained from A. sinensis to investigate the factors that influence the chemical transformation of 1, the products formed, and the rationale for monitoring 1 in natural product preparations. Countercurrent separation was used to purify 1 from a supercritical fluid extract of A. sinensis, achieving 93.4% purity in a single step. Subsequent purification by preparative HPLC afforded 1 with a 98.0% purity. Providing a mass balance setting, we monitored chemical changes occurring to highly purified 1 under various conditions and at different time points, in sealed NMR tubes by quantitative 1H NMR (qHNMR). The nondestructive nature of NMR enabled a comprehensive assessment of degradation products. Moreover, in being a mole-based determination, the total intensity (integral) of all NMR signals intrinsically represents the theoretical mass balance within the sample solution. The results demonstrated that 1 is most stable while within the original plant material. Exposure to light had a profound impact on the chemical transformation of 1, leading to the formation of ligustilide dimers and trimers, as verified by both NMR and LC-HRMS studies. Moreover, the results shown for 1, augmented by other recent outcomes, have serious implications for the meaningful biological evaluation of NPs that exhibit instability/reactivity, while having a plethora of "promising" bioactivities reported in the literature and being frequently associated with unsubstantiated health claims.