Stachyodin A, a pterocarpan derivative with unusual spirotetrahydrofuran ring from the roots of Indigofera stachyodes

Anti-inflammatory flavonoid derivatives from the heartwood of Dalbergia odorifera T. Chen

Two pairs of flavonoid enantiomers (1a/1b and 2a/2b) together with three known analogues (3-5) were isolated from the heartwood of Dalbergia odorifera T. Chen. Their structures were elucidated by extensive spectroscopic analysis (1 D and 2 D NMR, UV, IR, and HRMS) and experimental and calculated ECD data. Compound 2 features an unusual 2-methyl-3(2H)-furanone moiety forming the C-ring of flavonoid, and its putative biosynthetic pathway is also proposed. Compounds 3‒5 exhibited significant inhibition of nitric oxide production in lipopolysaccharide-stimulated RAW264.7 cells with IC₅₀ values of 14.7 ± 0.3 μM, 40.2 ± 1.1 μM, and 3.2 ± 0.1 μM, respectively.

The structure characteristics, biosynthesis and health benefits of naturally occurring rare flavonoids

Rare flavonoids, a special subclass of naturally occurring flavonoids with diverse structures including pterocarpans, aurones, neoflavonoids, homoisoflavones, diphenylpropanes, rotenoids and 2-phenylethyl-chromones. They are mainly found in legumes with numerous health benefits. Rare flavonoids are regarded as minor flavonoids due to their very limited abundance in nature. This review gives an overview of the natural occurrences of rare flavonoids from previous literatures. Recent findings on the biosynthesis of rare flavonoids have been updated by describing their structural characteristics and classifications. Recent findings on the health benefits of rare flavonoids have also been compiled and discussed. Natural rare flavonoids with various characteristics from different subclasses from plant-based food sources are stated. They show a wide range of health benefits, including antibacterial, anticancer, anti-osteoporosis and antiviral activities. Studies reviewed suggest that rare flavonoids possessing different skeletons demonstrate different characteristic bioactivities by discussing their mechanism of actions and structure-activity relationships. Besides, recent advances on the biosynthesis of rare flavonoids, such as pterocarpans, rotenoids and aurones are well-known, while the biosynthesis of other subclasses remain unknown. The perspectives and further applications of rare flavonoids using metabolic engineering strategies also be expected.

Diverse flavonoids from the roots of Indigofera stachyodes

Three new flavonoids , 4'- O - β - D -glucopyranosyl-2 S ,3 R -3,7-dihydroxy-3'-methoxyflavan ( 1 ), (3 R )-7,4'-dihydroxy-5,3'-methoxychalcone ( 2 ), (3 S )-7,2',3'-trihydroxy-6,4'-dimethoxylisoflavan ( 3 ), and one new natural occurring product, (3 S )-6,2',3'-trihydroxy-7,4'-dimethoxylisoflavan ( 4 ), together with eleven known ones ( 5 - 15 ), were isolated from the roots of Indigofera stachyodes . The structures of these compounds were confirmed by UV, IR, MS, and NMR spectroscopic analysis. The absolute configurations of new compounds were elucidated by ECD spectra and chemical method. All the isolated flavonoids were screened for their antioxidant abilities to scavenge DPPH and ABTS + . As results, compounds 2 - 4 , 10 , and 15 exhibited remarkable scavenging activity against both ABTS + and DPPH, with the IC 50 values less than 20 μ M. In addition, compounds 1 , 6 - 9 , and 13 exhibited potential antioxidant scavenging activities, IC 50 values were in the rang of 17.96～85.91 μ M.

Novel flavonolignans from the roots of Indigofera stachyodes

Two pairs of new enantiomeric flavonolignans, ±stachyols A and B (±1 and ± 2), along with two novel isoflavanelignans, stachyols C and D (3 and 4) were isolated from the roots of Indigofera stachyodes. Their chemical structures and absolute configurations were determined using nuclear magnetic resonance and comparison of experimental and theoretical electronic circular dichroism (ECD) spectra, as well as quantum chemical calculations. Of those compounds, 1 and 2 represented the first examples of flavonolignans with 5-deoxyflavonoids adduct phenylpropanoids. Moreover, 3 and 4 possess an unprecedented skeleton with isoflavanes adduct phenylpropanoids. The antioxidant activity was evaluated for all compounds in terms of ABTS⁺ and DPPH bioassays. Compounds 3 and 4 exhibited significant radical-scavenging activity in the ABTS⁺ assay, with IC₅₀ values of 15.15 and 5.83 μM, respectively.

Total Synthesis of Stachyodin A via One-Pot Suzuki Coupling for Quick Construction of Carbon Skeleton

Stachyodin A, possessing a unique spirotetrahydrofuran ring system, was isolated from the roots of Indigofera stachyodes in 2018. The first total synthesis of racemic stachyodin A was accomplished in 14 steps. The efficient stereoselective synthetic route involved one-pot Suzuki coupling and stereocontrolled epoxidation followed by reductive opening and spirocyclization.

A Novel Pterocarpan Derivative From the Roots of Sophora flavescens

Flavescensin A (1), a novel rearrangement derivative of pterocarpan with an unusual spirotetrahydrofuran ring, along with 7 known pterocarpans were isolated from the roots of Sophora flavescens using several different chromatographic separations. The planar structure of 1 was elucidated by their nuclear magnetic resonance spectroscopic and high-resolution electrospray ionization mass spectrometry data, and the absolute configuration of 1 was determined on the basis of electronic circular dichroism data. Putative biosynthetic pathway toward 1 was proposed. In addition, all of the compounds were evaluated for their anti-influenza virus and anti-inflammatory activities.

A review of traditional uses, phytochemistry and pharmacology of the genus Indigofera

ETHNOPHARMACOLOGICAL RELEVANCE

Indigofera is the third-largest genus in the family of Fabaceae, with approximately 750 species. It is distributed across all tropical regions. Indigofera species are widely employed in traditional medicine all around the world, against many ailments. Thus, based on these medicinal properties, various investigations have been undertaken in order to appraise the pharmacological activities and the chemical composition of these species. A recent paper provides a summary of the phytochemistry and pharmacology of the genus Indigofera. Consequently, this review is a continuation of this previous study by updating some data and adding information about the phylogeny and traditional uses of the genus.

AIM OF THE STUDY

To provide an overview of the phylogeny, traditional uses, phytochemistry, pharmacology and toxicity of the genus Indigofera, and to identify the remaining gaps and thus supply a basis for further investigations.

MATERIALS AND METHODS

A review of the literature was performed by consulting scientific databases such as 'ScienceDirect', 'PubMed', 'Google Scholar' and 'SpringerLink' and using the keyword Indigofera.

RESULTS

Over 60 Indigofera species are reported in traditional medicine. The uses depend on the country and the species, but similarities have been noticed. Indeed, treatments of gastrointestinal disorders, inflammatory conditions and pain, skin ailments, and respiratory and infectious diseases are recurring. Phytochemical studies have led to the identification of more than 200 compounds, notably flavonoids and terpenoids. Many pharmacological activities have been demonstrated, particularly antimicrobial, cytotoxic and anti-inflammatory activities, and thus allowed to assert most of the traditional uses of the genus. Some active compounds have been isolated and have shown remarkable therapeutic potential, like the alkaloid indirubin, which is currently being clinically trialed.

CONCLUSIONS

The data on the genus Indigofera are extensive, but gaps still remain. Indeed, some promising species have not been assessed for their phytochemistry and/or pharmacology and thus remain unexplored. Moreover, relatively few active compounds have been isolated and tested for their biological activity, and studies to explain their mechanism of action are nearly inexistent. Furthermore, some pharmacological studies have inappropriate methodologies that make the results difficult to interpret. Consequently, further in-depth and relevant research is required to supplement the knowledge on this wide-ranging genus and to confirm its reported therapeutic potential.

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.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as vlasoulamine A from Vladimiria souliei.