Diarylheptanoids from Dioscorea villosa (Wild Yam)

The genus Dioscorea L. (Dioscoreaceae), a review of traditional uses, phytochemistry, pharmacology, and toxicity

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Dioscorea, a member of the Dioscoreaceae family, comprises approximately 600 species and is widely distributed across temperate and tropical regions such as Asia, South Africa, and North America. The traditional medicinal uses of Dioscorea have been documented in Asian and African pharmacological systems. In Asia, this genus is traditionally used to treat respiratory illnesses, rheumatism, diabetes, diarrhea, dysentery, and other conditions. In Africa, this genus has been used to treat human immunodeficiency virus and ring worms. However, the traditional medicinal practices in North America rarely mention the use of this genus.

AIM OF THE STUDY

The aim of this review is to comprehensively review the genus Dioscorea, focusing on its traditional uses, phytochemical constituents, pharmacological activities, and potential toxicities. The research also aims to highlight the valuable bioactive compounds within Dioscorea and emphasize the need for further investigations into acute and chronic toxicity, activity mechanisms, molecular markers, and other relevant factors to contribute to the discovery of novel pharmaceuticals.

MATERIALS AND METHODS

A search for available information on Dioscorea was conducted using scientific databases, including PubMed, ISI-WOS, Scopus, and Google Scholar, as well as recent academic publications from reputable publishers and other literature sources. The search was not limited by language and spanned the literature published between 1950 and 2022.

RESULTS

This article provides a comprehensive review of the Dioscorea genus, focusing on its traditional uses, phytochemical constituents, pharmacological activities, and potential toxicities. Extensive research has been conducted on this genus, resulting in the isolation and examination of over 1000 compounds, including steroids, terpenoids, and flavonoids, to determine their biological activities. These activities include anti-tumor, anti-inflammatory, immunomodulatory, neuroprotective, hypoglycemic, and hypolipidemic effects. However, some studies have indicated the potential toxicity of high doses of Dioscorea, highlighting the need for further investigations to assess the safety of this genus. Additionally, this review explores potential avenues for future research and discusses the challenges associated with a comprehensive understanding of the Dioscorea genus.

CONCLUSIONS

Based on the existing literature, it can be concluded that Dioscorea is a valuable source of bioactive compounds that have the potential to treat various disorders. Future research should prioritize the investigation of acute and chronic toxicity, activity mechanisms, molecular markers, and other relevant factors. This review provides a comprehensive analysis of the Dioscorea genus, emphasizing its potential to enable a deeper exploration of the biological activity mechanisms of these plants and contribute to the discovery of novel pharmaceuticals.

Asymmetric total synthesis of diosniponols A and B

A concise asymmetric total synthesis of diosniponols A and B has been achieved based on an enantioselective Jacobsen kinetic resolution of racemic epoxide and the important 2,3-dihydro-4H-pyran-4-one moiety being installed by the metal-free δ-hydroxyalkynone rearrangement catalyzed by p-TsOH. A diastereoselective catalytic hydrogenation set the required all-syn stereochemistry leading to diosniponol A, which then, under the Mitsunobu inversion conditions, provided diosniponol B. The structure and absolute stereochemistry of the natural products were further confirmed.

Isolation and identification of active ingredients and biological activity of Dioscorea nipponica Makino

This study reported the isolation and identification of bioactive compounds from Dioscorea nipponica Makino, a plant used in traditional medicine for various ailments. Nine compounds were isolated, including a new compound named as diosniposide E, which was elucidated by analyzing its ¹H-NMR, ¹³C-NMR, DEPT, COSY, HMBC and MS data and comparing them with data available in literature. The other eight compounds were identified as known compounds. Theoretical calculations of energy and the generation of a molecular electrostatic potential surface map were employed to assess the antioxidant capacity of nine compounds, the calculation results exhibited that compounds 5 and 6 had strong antioxidant capacities. To further evaluate the antioxidant activities of the investigated compounds, the DPPH and ABTS assays were conducted. The results from the DPPH scavenging activity test revealed that compounds 4-6 exhibited enhanced scavenging activities compared to L-ascorbic acid, while displaying similar efficacy to trolox. Moreover, the ABTS scavenging activities of compounds 4-6 were found to surpass those of L-ascorbic acid and trolox. In terms of α-glucosidase inhibition, compounds 3 and 4 displayed remarkable inhibitory activities that surpassed the effects of acarbose. Additionally, compound 2 exhibited potent anticholinesterase activities, outperforming donepezil. This research provides insights into the potential bioactive compounds present in Dioscorea nipponica Makino and may contribute to its use in traditional medicine.

Geraniol-Derived Monoterpenoid Glucosides from Rhodiola rosea: Resolving Structures by QM-HifSA Methodology

Monoterpenoids are integral to the chemical composition of the widely used adaptogenic dietary supplement Rhodiola rosea. The present study expands the chemical space and stereochemical information about these taxon-specific constituents from the isolation and characterization of five geraniol-derived glucosides, 1-5. While 1 and 2 exhibited almost identical NMR spectra and shared the same 2D structure ascribed to the 4-hydroxygeraniolglucoside previously described as rosiridin, the NMR-based Mosher ester method revealed the enantiomeric nature of their aglycone moieties. This marks the first report of enantiomeric aglycones among geraniol derivatives. These findings also resolve the long-standing dispute regarding the absolute configuration of rosiridin and congeneric C-4 hydroxylated geraniols and may help explain incongruent bioactivity reports of R. rosea extract. Moreover, the three previously undescribed geranioloids 3-5 were fully characterized by extensive spectroscopic analysis. Quantum mechanics-driven 1H iterative functionalized spin analysis (QM-HifSA) was performed for all isolates and provides detailed NMR spin parameters, with adequate decimal place precision, which enable the distinction of such close congeners exhibiting near identical NMR spectra with high specificity. The outcomes also reinforce the importance of reporting chemical shifts and coupling constants with adequate decimal place precision as a means of achieving specificity and reproducibility in structural analysis.

NMR-Based Chromatography Readouts: Indispensable Tools to “Translate” Analytical Features into Molecular Structures

Gaining structural information is a must to allow the unequivocal structural characterization of analytes from natural sources. In liquid state, NMR spectroscopy is almost the only possible alternative to HPLC-MS and hyphenating the effluent of an analyte separation device to the probe head of an NMR spectrometer has therefore been pursued for more than three decades. The purpose of this review article was to demonstrate that, while it is possible to use mass spectrometry and similar methods to differentiate, group, and often assign the differentiating variables to entities that can be recognized as single molecules, the structural characterization of these putative biomarkers usually requires the use of NMR spectroscopy.

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world’s most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage “If you don’t seek, you don’t find”. Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

NMR technique and methodology in botanical health product analysis and quality control

Botanicals have played an important role in maintaining human health and well-being throughout history. During the past few decades in particular, the use of botanical health products has gained more popularity. Whereas, quality, safety and efficacy concerns have continuously been critical issues due to the intrinsic chemical complexity of botanicals. Chemical analytical technologies play an imperative role in addressing these issues. Nuclear magnetic resonance (NMR) spectroscopy has proven to be a powerful and useful tool for the investigation of botanical health products. In this review, NMR techniques and methodologies that have been successfully applied to the research and development of botanical health products in all stages, from plants to products, are discussed and summarized. Furthermore, applications of NMR together with other analytical techniques in a variety of domains of botanical health products investigation, such as plant species differentiation, adulteration detection, and bio-activity evaluation, are discussed and illustrated with typical examples. This article provides an overview of the potential uses of NMR techniques and methodologies in an attempt to further promote their recognition and utilization in the field of botanical health products analysis and quality control.

Antioxidant and Cytoprotective Effects of New Diarylheptanoids from Rhynchanthus beesianus

Rhynchanthus beesianus (Zingiberaceae) has been an important food spice and vegetable in southern China. Fifteen phenolic compounds (1-15) including three new diarylheptanoids, rhynchanines A-C (1-3) and one new phenylpropanoid, 4-O-methylstroside B (9), were isolated from R. beesianus rhizomes. The structures of new compounds were elucidated by comprehensive analyses through NMR, HRMS technique, acid hydrolysis, and Mosher's reaction. Among them, compound 5 is the first isolated natural product and its NMR data are reported. Most of the isolated compounds, especially 3-6 and 8, showed significant antioxidant activities on DPPH, ABTS⁺ radical scavenging, and FRAP assays. Furthermore, the antioxidant phenolic compounds were evaluated for their cytoprotective capacity against H₂O₂-induced oxidative stress in HepG-2 cells. Compounds 3 and 5 could significantly inhibit reactive oxygen species production, and compounds 3, 5, and 6 could remarkably prevent the cell apoptosis. Then, the R. beesianus rhizome, which contained phenolic compounds, might serve as a functional food for potential application on preventing oxidative stress-connected diseases.

Constituents of Two Dioscorea Species That Potentiate Antibiotic Activity against MRSA

The isolation of two diarylnonanoids from Dioscorea cotinifolia possessing antibiotic-potentiating activity against resistant strains of S. aureus are reported. The diarylnonanoids are a class of natural products similar in structure to the diarylheptanoids, which have a wide spectrum of reported biological activities. One of the diarylnonanoids (1) isolated possesses a chiral center, and to deduce its configuration, the modified Mosher ester method was used. Using both 1D and 2D NMR data, as many protons as possible were assigned to both the R- and S-MTPA esters, and the configuration of the chiral center in 1 was determined to be R. Both the chiral and achiral diarylnonanoid (2) exhibited potent antibiotic-potentiating activity with the chiral natural product showing a greater tetracycline-potentiating activity than 2. Interestingly, 2 gave a higher norfloxacin-potentiating activity with a resultant higher efflux pump inhibitory activity. Manipulation of the structure of the diarylnonanoids through synthesis could lead to improved biological activity.

Structural Elucidation of Presilphiperfolane-7α,8α-diol, a Bioactive Sesquiterpenoid from Pulicaria vulgaris: A Combined Approach of Solvent-Induced Chemical Shifts, GIAO Calculation of Chemical Shifts, and Full Spin Analysis

Structural elucidation of a new triquinane sesquiterpenoid, presilphiperfolane-7α,8α-diol, 1a, isolated from Pulicaria vulgaris, was accomplished by combining solvent-induced removal of chemical shift degeneracy and computational (DFT-GIAO) prediction of NMR spectra with the analysis of ¹H NMR splitting patterns. In addition to extensive NMR experiments (in 10 different solvents), MS, and FTIR, the identity of 1a was also confirmed by chemical transformations. The applied approach can facilitate structural elucidation of organic molecules and decrease the probability of an erroneous identification, permitting an unambiguous stereochemical elucidation and full NMR assignment. The pharmacological/toxicological profile of 1a was evaluated in several different models.

Three New Bibenzyls from the Twigs of Smilax longifolia

Three new bibenzyl compounds, 1-3, were isolated along with the previously known bibenzyls 4-6, one diarylpropanoid 7, and three diarylheptanoids 8-10 from the twigs of Smilax longifolia. The structures of the new compounds were elucidated by analyzing their spectroscopic data and comparing them with those of known compounds. Diarylheptanoid 9 exhibited potent lethality in the brine shrimp lethality test (BST).

Characterization of diarylheptanoids: An emerging class of bioactive natural products

Diarylheptanoids are a class of secondary plant metabolites with a wide variety of bioactivity. Research on their phytochemistry and phytoanalysis is rapidly growing and the number of identified structures bearing the aryl-C₇-aryl skeleton is at present approaching 500. Historically, the yellow pigment curcumin has been characterized as the first diarylheptanoid and the extensive research on naturally occurring analogues is still ongoing. In this review, studies dealing with the characterization of linear and cyclic derivatives are discussed from the phytoanalytical point of view. Isolation, fractionation and purification strategies from natural sources along with their chromatographic behavior and structural characteristics are discussed. The role of various techniques used for the extraction (such as Soxhlet extraction, sonication, maceration/percolation, microwave-assisted extraction, supercritical carbon dioxide extraction); isolation (liquid-liquid extraction, column chromatographic techniques, preparative thin-layer and high-performance liquid chromatography, centrifugal partition chromatography, counter-current chromatography); separation (thin-layer chromatography, high-performance liquid chromatography, gas chromatography, capillary electrophoresis) and structural characterization (UV/Vis spectroscopy, infrared spectroscopy, X-ray crystallography, mass spectrometry, nuclear magnetic resonance spectroscopy and circular dichroism spectroscopy) are critically reviewed.

Germacranes and m-menthane from Illicium lanceolatum

Three new germacrane sesquiterpenes and a new m-menthane monoterpene were isolated together with four known compounds from the pericarp of Illicium lanceolatum, an adulterant to star anise (Illicium verum). All compounds were isolated from Illicium plants for the first time. The absolute stereochemistry of all germacranes and m-menthane was established by a combination of NMR and the modified Mosher’s ester method. The biological activity was evaluated on SH-SY5Y neuroblastoma cell line. (1S,5R,7R)-1,5-Dihydroxygermacra-4(15),10(14),11(12)-triene (at 62.5 µM) and (1R,5R,7R)-1,5-dihydroxygermacra-4(15),10(14),11(12)-triene (at 15.6 µM) promoted the proliferation of SH-SY5Y by 36.2% and 45.8%, respectively, after 48 h incubation, indicating potential neurotrophic activity.

Universal quantitative NMR analysis of complex natural samples

Nuclear Magnetic Resonance (NMR) is a universal and quantitative analytical technique. Being a unique structural tool, NMR also competes with metrological techniques for purity determination and reference material analysis. In pharmaceutical research, applications of quantitative NMR (qNMR) cover mostly the identification and quantification of drug and biological metabolites. Offering an unbiased view of the sample composition, and the possibility to simultaneously quantify multiple compounds, qNMR has become the method of choice for metabolomic studies and quality control of complex natural samples such as foods, plants or herbal remedies, and biofluids. In this regard, NMR-based metabolomic studies, dedicated to both the characterization of herbal remedies and clinical diagnosis, have increased considerably.

Lipidated steroid saponins from Dioscorea villosa (wild yam)

Two groups of lipidated steroid saponins including seven new compounds (2, 3, 5, and 7-10) were isolated from the widely used botanical, wild yam (Dioscorea villosa), employing a fractionation protocol of metabolomic mining. This methodology recently led to the isolation of 14 diarylheptanoids from the same plant. Together with these lipidated steroid saponins, they establish additional new markers for D. villosa. The lipidation of steroids with analog long-chain fatty acids containing different degrees of unsaturation generates an entire series of compounds which are difficult to purify and analyze. The structures of the two series of lipidated steroid saponins (series A and B) were established by a combination of 1D and 2D NMR as well as GC-MS after chemical modification. Series A was determined to be a mixture of lipidated spirostanol glycosides (1-5), while series B (6-10) was proved to be a mixture of five lipidated clionasterol glucosides. The latter group represents the first derivatives of clionasterol to be found in D. villosa. The discovery of this specific structural type of aliphatic esters of steroid saponins expands the characterization of the secondary metabolome of D. villosa. It may also inspire biological studies which take into account the lipophilic character and significantly altered physiochemical characteristics of these otherwise relatively polar phytoconstituents.

Anti-neuroinflammatory diarylheptanoids from the rhizomes of Dioscorea nipponica

In a continuing search for bioactive constituents from Dioscoreaceae medicinal plants, two new cyclic diarylheptanoids, diosniponol A (1) and B (2), together with 10 known compounds (3-12) were isolated from the rhizomes of Dioscorea nipponica. The structures of these new compounds were determined by spectroscopic analyses, including extensive two-dimensional nuclear magnetic resonance, high-resolution mass spectrometry, and optical rotation. All isolated compounds 1-12 were evaluated for their effects on nitric oxide (NO) production in murine microglia cell line BV-2. Compounds 8 and 11 showed potent inhibitory activities on NO production (IC50 13.36 and 14.36 μM, respectively) without cell toxicity in lipopolysaccharide-activated BV-2 cells.