Peroxynitrite-Scavenging Glycosides from the Stem Bark of Catalpa ovata

Iridoids and derivatives from Catalpa ovata with their antioxidant activities

Six new iridoid derivatives (1-6)，together with twelve known compounds (7-18), were isolated and identified from the dried fruits of Catalpa ovata G. Don. Their chemical structures were mainly established through the relative spectroscopic data, while the absolute configurations of compounds 2 and 3 were elucidated on the electronic circular dichroism calculations. Their antioxidant activities were evaluated by activating the Nrf2 transcriptional pathway in 293 T cells in vitro. Among them, Compounds 1, 3, 4, 6-8, 10-12, 14, 15, 17 and 18 showed significant Nrf2 agonistic effect compared with the control group at 25 μM. Finally, The hypothetical biosynthetic pathway for 1-13 was discussed.

Angiotensin I-Converting Enzyme-Inhibitory Activity and Phytochemical Profile of Constituents of the Leaves of Rehmannia glutinosa f. hueichingensis

The root of Rehmannia glutinosa Liboschitz forma hueichingensis HSIAO has been used as a tonic and treatment for urinary and skin disorders in Japanese Kampo medicine. Phytochemical investigation of the root has been well reported, but that of the leaves is limited. To explore the potential value of R. glutinosa leaves, we focused on the angiotensin I-converting enzyme (ACE)-inhibitory activity. The leaf extract exhibited ACE-inhibitory activity, and the inhibitory potency of leaves was stronger than that of roots. Using this activity as an indicator, we isolated linaride (1), 6-O-hydroxybenzoyl ajugol (2), acteoside (3), leucosceptoside A (4), martynoside (5), luteolin (6), apigenin (7), and chrysoeriol (8) by separating and purifying the extract. We then examined the ACE-inhibitory activities of 1-8, catalpol (9), aucubin (10), ajugol (11), and echinacoside (12). Among them, 3, 6, and 12 displayed the most potent inhibitory activity. A simultaneous analytical method was also developed using compounds contained in R. glutinosa leaves and roots, and their contents were compared. The method consisted of extraction with 50% aqueous methanol under sonication for 60 min and LC/MS measurement. R. glutinosa leaves tended to have higher levels of majority of the analytes than the roots, including 3 and 6, which had higher ACE-inhibitory activity. These results suggest that 3 and 6 contribute to the ACE-inhibitory activity of R. glutinosa leaves, which may represent a useful medicinal resource for hypertension.

Scalable total synthesis of natural vanillin-derived glucoside ω-esters

The first total synthesis of vanilloloside, calleryanin, and a series of naturally occurring ω-esters of vanilloloside was realized through direct glycosylation of vanillin-based aglycones or late-stage derivatization of vanilloloside. All aglycones and their fragments were synthesized from vanillin as the sole aromatic precursor. Subsequently, these intermediates were used to construct various vanillin-derived glucoside ω-esters using a mild acidic deacetylation as the key synthetic step, providing the final products in the total yields of 10-50% and general purity of >95%. Additionally, the first operationally simple and sustainable synthesis of litseafoloside B was realized on large scale, avoiding the use of toxic solvents and reagents, providing an attractive alternative to isolation of this and other similar compounds from plant sources.

Cytotoxic cardenolides from Calotropis gigantea

Sixteen cardiac glycosides, including five previously undescribed compounds, were extracted and purified from whole plants of Calotropis gigantea (L.). Spectroscopic data and electronic circular dichroism (ECD) analyses were used to determine their structures. Calogiganin C is the first naturally occurring example of a cardenolide containing a 7-membered lactone in ring A. The cytotoxic activities of these compounds against A172, U251, AGS, PANC-1, HepG2, HCT116 and NCI-H226 cell lines were evaluated. Four of them exhibited the most potent growth inhibitory activity against a panel of human cancer cell lines, including A172, U251, AGS, PANC-1 and HCT116. Notably, uscharidin and calotropin showed pronounced cytotoxicities at low nanomolar concentrations against A172 and U251 cells, and possible cell death mechanism studies manifested that these two compounds induced G2/M cell cycle arrest, which demonstrated promising anticancer potential.

Phenolic constituents isolated from Senna tora sprouts and their neuroprotective effects against glutamate-induced oxidative stress in HT22 and R28 cells

The consumption of sprouts has been steadily increasing due to their being an excellent source of nutrition. It is known that the bioactive constituents of legumes can be increased after germination. In this study, the extract from Senna tora sprouts is shown to exhibit improved radical scavenging activities and better neuroprotective effects in HT22 hippocampal neuronal (HT22) and R28 retina precursor (R28) cells than those from seeds due to an increased content of phenolic constituents, especially compounds 1 and 3-6. A phytochemical investigation of S. tora sprouts resulted in the isolation of two new naphthopyrone glycosides (1-2) with 27 previously reported compounds. Their structures were determined via interpreting spectroscopic data. Compounds 1 and 3-6 were found to possess radical scavenging activities and neuroprotective effects against oxidative stress in both neuronal cells. Hence, Senna tora sprouts and their constituents may be developed as natural neuroprotective agents via antioxidative effects.

Metabolite Profile of Cucurbitane-Type Triterpenoids of Bitter Melon (Fruit of Momordica charantia) and Their Inhibitory Activity against Protein Tyrosine Phosphatases Relevant to Insulin Resistance

Qualitative analysis of cucurbitane-type triterpenoids of bitter melon (fruit of Momordica charantia L.) using ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry revealed 27 promising cucurbitane-type triterpenoids, and LC/MS-guided chemical analysis of M. charantia fruit extract led to the isolation and structural characterization of 22 cucurbitane-type triterpenoids (1-22), including 8 new cucurbitane-type triterpenoidal saponins, yeojoosides A-H (1-8). The structures of the new compounds (1-8) were elucidated by spectroscopic methods, including 1D and 2D NMR and high-resolution electrospray ionization mass spectrometry. Their absolute configurations were assigned by quantum chemical electronic circular dichroism calculations, chemical reactions, and DP4+ analysis using gauge-including atomic orbital NMR chemical shift calculations. All isolated compounds (1-22) were examined for inhibitory activity against protein tyrosine phosphatases relevant to insulin resistance. Nine compounds (7, 8, 9, 11, 14, 15, 19, 20, and 21) showed selective inhibitory effects of over 70% against PTPN2. The present results suggested that these compounds would be potential antidiabetic agents.

The Chemical Constituents from Fruits of Catalpa bignonioides Walt. and Their α-Glucosidase Inhibitory Activity and Insulin Secretion Effect

Catalpa pod has been used in traditional medicine for the treatment of diabetes mellitus in South America. Studies on the constituents of Catalpa species have shown that it is rich in iridoids. In the present study, three previously undescribed compounds (2–4), including two secoiridoid derivatives along with twelve known compounds, were isolated from the fruits of Catalpa bignonioides Walt. In addition, fully assigned ¹³C-NMR of 5,6-dihydroxy-7,4’-dimethoxyflavone-6-O-sophoroside (1) is reported for the first time in the present study. The structures of compounds were determined on the basis of extensive spectroscopic methods, including UV, IR, 1D, and 2D NMR, mass spectroscopy, and CD spectroscopic data. All the isolated compounds were evaluated for α-glucosidase inhibitory activity. Among the tested compounds, compounds 2, 3, and 9 exhibited significant inhibitory activity against α-glucosidase enzyme assay. Meanwhile, the effect of compounds 2, 3, and 9 on glucose-stimulated insulin secretion (GSIS) was measured using pancreatic β-cells. Compounds 2, 3, and 9 exhibited non-cytotoxicity-stimulated insulin secretion in INS-1 cells. The expression levels of proteins associated with β-cell function and insulin secretion such as phosphorylation of total insulin receptor substrate-2 (IRS-2), phosphatidylinositol 3-kinase (PI3K), Akt, activated pancreatic duodenal homeobox-1 (PDX-1), and peroxisome proliferator-activated receptor-γ (PPAR-γ) were increased in INS-1 cells after treatment with compounds 2, 3, and 9. The findings of the present study could provide a scientific warrant for their application as a potential antidiabetic agent.

Diterpenoids caryopterisoids D - Q and iridoid glucoside derivatives caryopterisides F - H from Caryopteris glutinosa

Fourteen undescribed diterpenoids caryopterisoids D - Q, three undescribed iridoid glucoside derivatives caryopterisides F - H, and 8 known diterpenoids were isolated from the 95% aqueous ethanolic extract of Caryopteris glutinosa. Their structures were elucidated on the basis of spectroscopic data analysis and chemical derivation studies. The structure and absolute configuration of caryopterisoid D were confirmed by X-ray crystallographic analysis. Caryopterisoids K and R, royleanone, 6α-hydroxydemethylcryptojaponol, and teuvincenone E were shown to reduce the biosynthesis of estrogen E2 with IC₅₀ values from 0.25 to 3.06 μM in cell-based estrogen biosynthesis assays system.

Phenolic glycosides from Oroxylum indicum

Two new phenolic glycosides, oroxylumosides A (1) and B (2), along with four known compounds darendoside A (3), leucosceptoside A (4), acteoside (5) and decaffeoylacteoside (6) were isolated from the stem bark of Oroxylum indicum. Their structures were elucidated by extensive analysis of the 1 D and 2 D NMR as well as HR-ESI-QTOF-MS. In addition, compounds 1 - 4 exhibited inhibitory effects on NO production in LPS-stimulated BV2 microglial cell line with IC₅₀ values of 58.2 ± 2.9, 70.6 ± 3.5, 56.8 ± 2.8 and 61.1 ± 3.1 µM, respectively.

Triple-Negative Breast Cancer Cells Exhibit Differential Sensitivity to Cardenolides from Calotropis gigantea

Triple-negative breast cancers (TNBC) are aggressive and heterogeneous cancers that lack targeted therapies. We implemented a screening program to identify new leads for subgroups of TNBC using diverse cell lines with different molecular drivers. Through this program, we identified an extract from Calotropis gigantea that caused selective cytotoxicity in BT-549 cells as compared to four other TNBC cell lines. Bioassay-guided fractionation of the BT-549 selective extract yielded nine cardenolides responsible for the selective activity. These included eight known cardenolides and a new cardenolide glycoside. Structure-activity relationships among the cardenolides demonstrated a correlation between their relative potencies toward BT-549 cells and Na+/K+ ATPase inhibition. Calotropin, the compound with the highest degree of selectivity for BT-549 cells, increased intracellular Ca2+ in sensitive cells to a greater extent than in the resistant MDA-MB-231 cells. Further studies identified a second TNBC cell line, Hs578T, that is also highly sensitive to the cardenolides, and mechanistic studies were conducted to identify commonalities among the sensitive cell lines. Experiments showed that both cardenolide-sensitive cell lines expressed higher mRNA levels of the Na+/Ca2+ exchanger NCX1 than resistant TNBC cells. This suggests that NCX1 could be a biomarker to identify TNBC patients that might benefit from the clinical administration of a cardiac glycoside for anticancer indications.

Antifungal Phenols from Woodfordia uniflora Collected in Oman

Woodfordia uniflora is a flowering shrub unique to the Dhofar region of Oman and is used locally as a sedative and remedy for skin infection. However, no study to date has examined the pharmacological properties of this plant, and studies regarding phytochemicals present in W. uniflora are limited. Herein, phytochemical screening of the extract of W. uniflora was performed using LC/MS. Three new phenolic compounds, (±)-woodfordiamycin (1), woodfordic acid (2), and rhamnetin 3-O-(6″-galloyl)-β-d-glucopyranoside (3), together with 16 known compounds 4-19, were isolated from the antifungal fraction of the extract. The structures of the new compounds were established by NMR and HR-MS data, and their absolute configurations were established using chemical transformations, including Mosher's method, comparison of experimental and calculated electronic circular dichroism data, and gauge-including atomic orbital NMR chemical shift calculations, followed by DP4+ analysis. The isolated compounds (1-19) were tested for antifungal activity against human fungal pathogens Cryptococcus neoformans and Candida albicans. Compounds (±)-1 and 8 showed antifungal activity against C. neoformans, with the lowest minimum inhibitory concentrations of 1.8-1.9 μM, which was ∼10-fold lower than that of the currently available antifungal drug fluconazole, while (±)-1, 8, and 19 showed antifungal activity against C. albicans.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

Megastigmane Derivatives from the Cladodes of Opuntia humifusa and Their Nitric Oxide Inhibitory Activities in Macrophages

Opuntia humifusa, known as the eastern prickly pear cactus and locally called "Cheonnyuncho" in Korea, is cultivated widely on Jeju Island, Korea. Phytochemical analysis of the methanolic extract of the cladodes of O. humifusa, for which previous research is relatively limited, was performed under the guidance of LC/MS-based analysis. As a result, one new megastigmane (1) and four new megastigmane glucosides (2-5) were isolated along with 18 known compounds (6-23). The structures of the new compounds were established by 1D and 2D NMR and HRESIMS, and their absolute configurations were established by chemical reactions, quantum chemical electronic circular dichroism calculations, and DP4+ analysis using the gauge-including atomic orbital NMR chemical shift calculations as well as the application of Snatzke's method. The isolated compounds (1-23) were tested for NO production inhibition in lipopolysaccharide (LPS)-induced RAW 264.7 cells to investigate their anti-inflammatory effects. Compounds 10 and 11 exhibited significant inhibitory effects on LPS-induced NO production in a dose-dependent manner. The potential mechanistic pathway of 10 and 11 was also investigated using Western blotting, indicating that compounds 10 and 11 inhibit NO through iNOS expression.

Lobatamunsolides A-C, Norlignans from the Roots of Pueraria lobata and their Nitric Oxide Inhibitory Activities in Macrophages

Phytochemical investigation of the methanol (MeOH) extract of Pueraria lobata roots, known as “kudzu”, combined with liquid chromatography/mass spectrometry (LC/MS)-based analysis, resulted in the identification of four norlignans (1–4), including three new norlignans, lobatamunsolides A–C (1–3), and five known isoflavonoids (5–9). The structures of the new compounds were elucidated by a combination of spectroscopic methods, including 1D and 2D nuclear magnetic resonance (NMR) and high resolution (HR)-electrospray ionization mass spectrometry (ESIMS), and their absolute configurations were determined by chemical reaction and quantum chemical electronic circular dichroism (ECD) calculations. The isolated compounds (1–9) were evaluated for their inhibitory effects on nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. Compound 9 displayed the strongest NO inhibitory effect and compound 2 showed a weak effect. The potential mechanism of the effect of compound 9 was investigated by analysis of its molecular docking on the active site of inducible nitric oxide synthase (iNOS), which showed the potential interactions of compound 9 with key amino acid residues and the heme cofactor of iNOS. The mechanism as the inhibition of transcriptional iNOS protein expression was confirmed by western blotting experiments.

Bioactivities of Natural Catalpol Derivatives

Catalpol, a famous molecule of iridoids, possesses extensive pharmacological activities. Our studies found that compounds with low-polarity substituents at the 6-O position of catalpol exhibited higher NF-κB inhibitory potency than catalpol. However, catalpol derivatives are not much focused. Here this review provides extensive coverage of naturally occurring catalpol derivatives discovered from 1888 until 2018. It covers their distribution, chemotaxonomic significance, chemical structures, and bioactivities from more than 200 peer-reviewed articles, and highlights the structure-activity relationship of catalpol derivatives.

Lignan Glycosides and Flavonoid Glycosides from the Aerial Portion of Lespedeza cuneata and Their Biological Evaluations

Lespedeza cuneata (Fabaceae), known as Chinese bushclover, has been used in traditional medicines for the treatment of diseases including diabetes, hematuria, and insomnia. As part of a continuing search for bioactive constituents from Korean medicinal plant sources, phytochemical analysis of the aerial portion of L. cuneata led to the isolation of two new lignan glycosides (1,2) along with three known lignan glycosides (3–7) and nine known flavonoid glycosides (8–14). Numerous analysis techniques, including 1D and 2D NMR spectroscopy, CD spectroscopy, HR-MS, and chemical reactions, were utilized for structural elucidation of the new compounds (1,2). The isolated compounds were evaluated for their applicability in medicinal use using cell-based assays. Compounds 1 and 4–6 exhibited weak cytotoxicity against four human breast cancer cell lines (Bt549, MCF7, MDA-MB-231, and HCC70) (IC₅₀ < 30.0 μM). However, none of the isolated compounds showed significant antiviral activity against PR8, HRV1B, or CVB3. In addition, compound 10 produced fewer lipid droplets in Oil Red O staining of mouse mesenchymal stem cells compared to the untreated negative control without altering the amount of alkaline phosphatase staining.