Total synthesis of the pyranoisoflavone kraussianone 1 and related isoflavones

Chemical and biosynthetic potential of Penicillium shentong XL-F41

Penicillium strains are renowned for producing diverse secondary metabolites with unique structures and promising bioactivities. Our chemical investigations, accompanied by fermentation media optimization, of a newly isolated fungus, Penicillium shentong XL-F41, led to the isolation of twelve compounds. Among these are two novel indole terpene alkaloids, shentonins A and B (1 and 2), and a new fatty acid 3. Shentonin A (1) is distinguished by an unusual methyl modification at the oxygen atom of the typical succinimide ring, a feature not seen in the structurally similar brocaeloid D. Additionally, shentonin A (1) exhibits a cis relationship between H-3 and H-4, as opposed to the trans configuration in brocaeloid D, suggesting a divergent enzymatic ring-expansion process in their respective fungi. Both shentonins A (1) and B (2) also feature a reduction of a carbonyl to a hydroxy group within the succinimide ring. All isolated compounds were subjected to antimicrobial evaluations, and compound 12 was found to have moderate inhibitory activity against Candia albicans. Moreover, genome sequencing of Penicillium shentong XL-F41 uncovered abundant silent biosynthetic gene clusters, indicating the need for future efforts to activate these clusters and unlock the full chemical potential of the fungus.

Flavonoids from the Roots of Sophora flavescens and Their Potential Anti-Inflammatory and Antiproliferative Activities

The phytochemical investigation of the roots of the traditional Chinese medicinal plant Sophora flavescens led to the isolation of two novel prenylflavonoids with an unusual cyclohexyl substituent instead of the common aromatic ring B, named 4',4'-dimethoxy-sophvein (17) and sophvein-4'-one (18), and 34 known compounds (1-16, 19-36). The structures of these chemical compounds were determined by spectroscopic techniques, including 1D-, 2D-NMR, and HRESIMS data. Furthermore, evaluations of nitric oxide (NO) production inhibitory activity against lipopolysaccharide (LPS)-treated RAW264.7 cells indicated that some compounds exhibited obvious inhibition effects, with IC₅₀ ranged from 4.6 ± 1.1 to 14.4 ± 0.4 μM. Moreover, additional research demonstrated that some compounds inhibited the growth of HepG2 cells, with an IC₅₀ ranging from 0.46 ± 0.1 to 48.6 ± 0.8 μM. These results suggest that flavonoid derivatives from the roots of S. flavescens can be used as a latent source of antiproliferative or anti-inflammatory agents.

The Suzuki-Miyaura Cross-Coupling-Claisen Rearrangement-Cross-Metathesis Approach to Prenylated Isoflavones

Isoflavones were synthesized via Suzuki-Miyaura coupling of 3-iodochromones and para-methoxybenzene- and para-phenolboronic acid. In our hands, conditions commonly used for similar cross couplings turned out to be unsuccessful or difficult to reproduce, for example, due to the unplanned partial cleavage of MOM-protecting groups. Using Pd(dba)₂ as a precatalyst and tricyclohexylphosphine as an activating ligand, reliable cross-coupling conditions were identified. In all cases, notably higher yields of isoflavones were obtained with para-phenolboronic acid than with para-methoxybenzene boronic acid. This observation and the commercial availability of para-phenolboronic acid suggest that for the synthesis of the important 3'-prenyl- or 3',5'-diprenylisoflavone substitution pattern a synthetic route that introduces the prenyl substituents after the Pd-catalyzed cross-coupling step, thereby avoiding laborious and protecting-group-intensive multistep syntheses of C-prenylated arene boronic acids, is advantageous.

Recent advances in the synthesis of natural products containing the phloroglucinol motif

Covering: June 2009 to 2021Natural products containing a phloroglucinol motif include simple and oligomeric phloroglucinols, polycyclic polyprenylated acylphloroglucinols, phloroglucinol-terpenes, xanthones, flavonoids, and coumarins. These compounds represent a major class of secondary metabolites which exhibit a wide range of biological activities such as antimicrobial, anti-inflammatory, antioxidant and hypoglycaemic properties. A number of these compounds have been authorized for therapeutic use or are currently being studied in clinical trials. Their structural diversity and utility in both traditional and conventional medicine have made them popular synthetic targets over the years. In this review, we compile and summarise the recent synthetic approaches to the natural products bearing a phloroglucinol motif. Focus has been given on ingenious strategies to functionalize the phloroglucinol moiety at multiple positions. The isolation and bioactivities of the compounds are also provided.

Chemical Constituents of the Flowers of Pueraria lobata and Their Cytotoxic Properties

The flower of Pueraria lobata (Puerariae Flos) is a reddish-purple to violet-purple flower that blooms between July and September. In our preliminary study, Puerariae Flos extract exhibited significant activity against a human ovarian cancer cell line. This research aims to identify the active compounds in Pueraria Flos. By repeated chromatography, one new tryptophan derivative (1), two new flavanones (4 and 5), and 19 known compounds, including tryptophan derivatives (2 and 3), flavonoids (6–9), isoflavonoids (10–20), a flavonolignan (21), and a phenolic compound (22), were isolated from a methanol extract of Puerariae Flos. The structures of new compounds were elucidated as 13-N-benzoyl-l-tryptophan-1-N-β-d-glucopyranoside (1), 2-hydroxy-5-methoxy-naringenin (4), and 2-hydroxy-5-methoxy-naringenin 7-O-β-d-glucopyranoside (5). Among the isolates, afromosin (17), tectorigenin (11), apigenin (8), glycitein (16), (-)-hydnocarpin (21), irilin D (12), irisolidone 7-O-glucoside (14), and genistein (10) showed cytotoxicity against human ovarian cancer cell line A2780. Apigenin (8) and (-)-hydnocarpin (21) were the most active (IC₅₀ values of 9.99 and 7.36 μM, respectively).

Scope and Applications of 2,3-Oxidative Aryl Rearrangements for the Synthesis of Isoflavone Natural Products

The reaction of flavanones with hypervalent iodine reagents was investigated with a view to the synthesis of naturally occurring isoflavones. In contrast to several previous reports in the literature, we did not observe the formation of any benzofurans via a ring contraction pathway, but could isolate only isoflavones, resulting from an oxidative 2,3-aryl rearrangement, and flavones, resulting from an oxidation of the flavanones. Although the 2,3-oxidative rearrangement allows a synthetically useful approach toward some isoflavone natural products due to the convenient accessibility of the required starting materials, the overall synthetic utility and generality of the reaction appear to be more limited than previous literature reports suggest.

Davidones F and G, Two Novel Flavonoids from Sophora davidii (Franch.) Skeels

An unprecedented novel flavanone davidone F (1) with a seven-membered ring side chain, and a novel flavanonol davidone G (2), along with 11 known flavonoids, were isolated from the ethyl acetate fraction of Sophora davidii (Franch.) Skeels. Their planar structures were established by UV, IR, HRESIMS, 1D and 2D NMR data. The relative configurations of 1 and 2 were determined by calculation of NMR chemical shift values, the absolute configuration of 1 and 2 were assigned by comparing their experimental and calculated electronic circular dichroism (ECD) spectra. Moreover, compounds 1–13 were screened for the translocation activity of glucose transporter 4 (GLUT-4), and the fluorescence intensity was increased to the range of 1.56 and 2.79 folds. Compounds 1 and 2 showed moderate GLUT-4 translocation activity with 1.64 and 1.79 folds enhancement, respectively, at a concentration of 20 μg/mL.

Anti-proliferative and anti-inflammatory prenylated isoflavones and coumaronochromones from the fruits of Ficus altissima

Ficus altissima, an evergreen arbor belonging to the Moraceae family, is mainly cultivated in the tropics and subtropics of South and Southeast Asia with the characteristic of exuberant vitality and luxuriant foliage. In this article, four new prenylated isoflavones (1-4), along with ten previously described isoflavones (5-14) and two known prenylated coumaronochromones (15 and 16) were firstly obtained from the fruits of F. altissima. Their structures were identified by various spectroscopic techniques including specific optical rotation, HR-ESI-MS and NMR. The isolated products were evaluated for their anti-proliferative activities against three human tumor cell lines (HepG2, MCF-7 and MDA-MB-231) through MTT assay. Compounds 2, 3 and 16 exhibited obvious anti-proliferative activities against MDA-MB-231 cell line and compounds 3, 13 and 16 showed effective cytotoxic effects on HepG2 cell line in a concentration-dependent manner, as verified by the colony formation assay, cell and nucleus morphological assessment and apoptosis assay. Meanwhile, compounds 5 and 12 exhibited significant inhibition activities on NO production in LPS-stimulated RAW 264.7 cell line compared with positive control indometacin. The phytochemical investigation of the fruits of F. altissima in this study could provide the evidence for the discovery of lead compounds.

Synthesis and Antifungal Activity of Chromones and Benzoxepines from the Leaves of Ptaeroxylon obliquum

This study reports the first total synthesis of the bioactive oxepinochromones 12-O-acetyleranthin (8) (angular isomer) and 12-O-acetylptaeroxylinol (9) (linear isomer). The antifungal activity of these compounds and their derivatives was determined against Candida albicans and Cryptococcus neoformans. Most compounds had good selectivity between the two fungi and showed moderate to good activity. 12-O-Acetyleranthin (8) had the highest activity against C. albicans, with an MIC value of 9.9 μM, while 12-O-acetylptaeroxylinol (9), the compound present in Ptaeroxylon obliquum, had the highest activity against C. neoformans, with an MIC value of 4.9 μM.

Making natural products from renewable feedstocks: back to the roots?

This review highlights the utilization of biomass-derived building blocks in the total synthesis of natural products.

Synthesis of Isoflavones by Tandem Demethylation and Ring-Opening/Cyclization of Methoxybenzoylbenzofurans

The unexpected conversion of benzoylbenzofurans into isoflavones through an intramolecular cascade that involves deprotection and ring-opening/cyclization is described. This was discovered in an investigation of the possible transformation of benzoylbenzofurans into coumaronochromones. This route affords isoflavones in two major steps from acetophenones and benzoquinones. The transformation was validated by synthesizing differently substituted isoflavone derivatives and further applied to a concise synthesis of a potential anticancer lead compound, glaziovianin A (1).

Enantioselective Total Synthesis of Natural Isoflavans: Asymmetric Transfer Hydrogenation/Deoxygenation of Isoflavanones with Dynamic Kinetic Resolution

A concise and highly enantioselective synthesis of structurally diverse isoflavans from a single chromone is described. The key transformation is a single-step conversion of racemic isoflavanones into virtually enantiopure isoflavans by domino asymmetric transfer hydrogenation/deoxygenation with dynamic kinetic resolution.

New Isoflavonoids from the extract of Rhynchosia precatoria (Humb. & Bonpl. ex Willd.) DC. and their antimycobacterial activity

ETHNOPHARMACOLOGY RELEVANCE

The evaluation of the antimycobacterial activity of extracts of medicinal plants used by Mayos against tuberculosis and respiratory problems, allowed the identification of Rhynchosia precatoria (Humb. & Bonpl. ex Willd.) DC (Fabaceae) as the best candidate to find new antimycobacterial compounds.

AIM OF THE STUDY

To isolate and characterize the compounds of R. precatoria responsible for the inhibitory and bactericidal activity against Mycobacterium tuberculosis H37Rv and Mycobacterium smegmatis ATCC 700084. To determine antimycobacterial synergistic effect of pure compounds and their selectivity index towards Vero cells.

MATERIALS AND METHODS

A total of six flavonoids were purified by silica gel column chromatography. Structural elucidation of the isolated compounds was achieved by using 1D and 2D NMR spectroscopy techniques. The configuration at the C-3 chiral center was established by quantum mechanical calculation of the electronic circular dichroism (ECD) spectrum. In vitro inhibitory and bactericidal activity against M. tuberculosis and M. smegmatis were determined with the redox indicator Alamar Blue (resazurin). Synergy was determined by X/Y quotient. Cytotoxicity was measured by MTT assay.

RESULTS

The isolated compounds were identified as precatorin A (1), precatorin B (2), precatorin C (3), lupinifolin (4), cajanone (5) and lupinifolinol (6). Compounds 1-3 are new. Compounds 1 to 5 inhibited the growth of M. tuberculosis (MIC ≥31.25µg/mL); compounds 1, 2, 4 and 5 killed the bacteria (MBC ≥31.25µg/mL) and also inhibited M. smegmatis (MIC ≥125µg/mL), while 1 and 4 also resulted bactericidal (MBC ≥125µg/mL). Compounds 4 and 5 presented synergistic effect (X/Y quotient value <0.5) at a concentration of 1/2 MIC of each compound in the combination. Cytotoxicity in murine macrophages (RAW 264.7 cells) gave IC₅₀ values of 13.3-46.98µM, for compounds 1-5.

CONCLUSIONS

In this work we isolated two new isoflavanones (1 and 2), and one new isoflavone (3) with a weak antimycobacterial activity. The (3R) absolute configuration was assigned to 1 by computational analysis of its ECD spectrum and to 2 and 5 by similarity of their ECD spectra with that of 1. We are also reporting by first time, activity against virulent strain of M. tuberculosis for compounds 4 and 5 and their antimycobacterial synergistic effect.

Eriosema (Fabaceae) Species Represent a Rich Source of Flavonoids with Interesting Pharmacological Activities

Many flavonoids have so far been isolated as main secondary metabolites in plant species of the genus Eriosema (Fabaceae), which contains approximately 160 species. A total of 52 flavonoids including isoflavones, dihydroflavonols, flavonols, flavanones, dihydrochalcones, isoflavanone and their pyrano or glucoside derivatives were isolated and characterized from the five species of this genus investigated to date. Total synthesis and semi-synthesis (acetylation, methylation, hydrogenation, and cyclization) of some isolated flavonoids were reported. Due to several significant pharmacological properties (antimicrobial, cytotoxicity, anti-mycobacterial, antioxidant, antiviral, erectile-dysfunction, vasodilatory and hypoglycemic) of the isolated flavonoids and derivatives, more scientists should be interested in investigating Eriosema species. The present review is the first to document all flavonoids that have been reported from the genus Eriosema to date together with their synthetic and semi-synthetic derivatives, and their pharmacological properties. Dihydrochalcones, which are precursors of other classes of flavonoids, are very rare in natural sources and their isolation from Eriosema species may explain the large number of flavonoids found in this genus. It appears that isoflavone could be a marker for species in this genus. The 83 flavonoids (1–83) documented include 52 isolates, 31 semi-synthetic and 3 totally synthetic derivatives. Data were obtained from Google scholar, Pubmed, Scifinder, Sciencedirect, and Scopus. With 52 different flavonoids isolated from only 5 of the approximately 160 species it shows the remarkable chemical diversity of this genus. This compilation of the biological activities and chemical composition may renew the interest of pharmacologists and phytochemists in this genus.

Design, Synthesis, and Evaluation of Genistein Analogues as Anti-Cancer Agents

Genistein is a bioactive isoflavone derived from soybeans. The tie-in between the intake of genistein and the decreased incidence of some solid tumors (including prostate cancer) has been demonstrated by epidemiological studies. The potential of genistein in treating prostate cancer has also been displayed by in vitro cell-based and in vivo animal experiments. Genistein has entered clinical trials for both chemoprevention and potential treatment of prostate cancer. Even though the low oral bioavailability has presented the major challenges to genistein's further clinical development, chemical modulation of genistein holds the promise to generate potential anti-prostate cancer agents with enhanced potency and/or better pharmacokinetic profiles than genistein. As part of our ongoing project to develop natural products-based anti-prostate cancer agents, the current study was undertaken to synthesize eight genistein analogues for cytotoxic evaluation in three prostate cancer cell lines (PC-3, DU-145, LNCaP; both androgen-sensitive and androgen-refractory cell lines), as well as one aggressive cervical cancer cell line (HeLa). Eight genistein analogues have been successfully synthesized with Suzuki-Miyaura coupling reaction as a key step. Their in vitro anti-cancer potential was evaluated by trypan blue exclusion assay and WST-1 cell proliferation assay against a panel of four human cancer cell lines. The acquired data suggest i) that the C-5 and C-7 hydroxyl groups in genistein are very important for the cytotoxicity and anti-proliferative activity; and ii) that 1-alkyl-1H-pyrazol-4-yl and pyridine-3-yl might act as good bioisosteres for the 4'-hydroxyphenyl moiety in genistein.

Palladium-catalyzed arylation of 2H-chromene: a new entry to pyrano[2,3-c]carbazoles

Various pyrano[2,3-c]carbazoles are synthesized in high yields over five steps from commercially available resorcinol. Palladium-catalyzed arylation remains a key step in this novel strategy. The versatility of this protocol has been demonstrated by the first total synthesis of naturally occurring carbazole clauraila C.

A New Prenylated Stilbene Derivative from the Roots of Cudrania Tricuspidata

A new prenylated stilbene, 2-dimethylallyl-3,5,2’,4′-tetrahydroxy-( E)-stilbene, cudrastilbene, and five known compounds, oxyresveratrol, naringenin, steppogenin, aromadendrin, and genistein were isolated from the roots of Cudrania tricuspidata. The structure of the new compound was established by spectroscopic methods. All the compounds were evaluated for their cytotoxicity against three human tumour cell lines (HepG2, HCT-116, and SGC-7901). Cudrastilbene showed weak cytotoxic activity against the HepG2 cell line with an IC50 of 40.19 μM.

Application of the Suzuki-Miyaura reaction in the synthesis of flavonoids

The application of the Suzuki-Miyaura reaction in the synthesis of flavonoids, an important class of natural products, is reviewed. This reaction has not only been employed to provide access to flavonoid nuclei, but has also been applied to the synthesis of dimeric flavonoids and in the synthesis of libraries of flavonoid derivatives for biological activity studies. The classes of flavonoids that are discussed are the chalcones, flavones, isoflavones, neoflavones, biflavones and derivatives of flavonoids obtained by C-C bond formation via the Suzuki-Miyaura reaction.