Structural variety and pharmacological potential of naphthylisoquinoline alkaloids

Naphthylisoquinoline alkaloids are a fascinating class of natural biaryl compounds. They show characteristic mono- and dimeric scaffolds, with chiral axes and stereogenic centers. Since the appearance of the last comprehensive overview on these secondary plant metabolites in this series in 1995, the number of discovered representatives has tremendously increased to more than 280 examples known today. Many novel-type compounds have meanwhile been discovered, among them naphthylisoquinoline-related follow-up products like e.g., the first seco-type (i.e., ring-opened) and ring-contracted analogues. As highlighted in this review, the knowledge on the broad structural chemodiversity of naphthylisoquinoline alkaloids has been decisively driven forward by extensive phytochemical studies on the metabolite pattern of Ancistrocladus abbreviatus from Coastal West Africa, which is a particularly "creative" plant. These investigations furnished a considerable number of more than 80-mostly new-natural products from this single species, with promising antiplasmodial activities and with pronounced cytotoxic effects against human leukemia, pancreatic, cervical, and breast cancer cells. Another unique feature of naphthylisoquinoline alkaloids is their unprecedented biosynthetic origin from polyketidic precursors and not, as usual for isoquinoline alkaloids, from aromatic amino acids-a striking example of biosynthetic convergence in nature. Furthermore, remarkable botanical results are presented on the natural producers of naphthylisoquinoline alkaloids, the paleotropical Dioncophyllaceae and Ancistrocladaceae lianas, including first investigations on the chemoecological role of these plant metabolites and their storage and accumulation in particular plant organs.

Nutritional and pharmacological potentials of orphan legumes: Subfamily faboideae

Legumes are a major food crop in many developing nations. However, orphan or underutilized legumes are domesticated legumes that have valuable properties but are less significant than main legumes due to use and supply restrictions. Compared to other major legumes, they are better suited to harsh soil and climate conditions, and their great tolerance to abiotic environmental circumstances like drought can help to lessen the strains brought on by climate change. Despite this, their economic significance in international markets is relatively minimal. This article is aimed at carrying out a comprehensive review of the nutritional and pharmacological benefits of orphan legumes from eight genera in the sub-family Faboidea, namely Psophocarpus Neck. ex DC., Tylosema (Schweinf.) Torre Hillc., Vigna Savi., Vicia L., Baphia Afzel. ex G. Lodd., Mucuna Adans, Indigofera L. and Macrotyloma (Wight & Arn.) Verdc, and the phytoconstituents that have been isolated and characterized from these plants. A literature search was conducted using PubMed, Google Scholar, and Science Direct for articles that have previously reported the relevance of underutilized legumes. The International Union for Conservation of Nature (IUCN) red list of threatened species was also conducted for the status of the species. References were scrutinized and citation searches were performed on the study. The review showed that many underutilized legumes have a lot of untapped potential in terms of their nutritional and pharmacological activities. The phytoconstituents from plants in the subfamily Faboideae could serve as lead compounds for drug discovery for the treatment of a variety of disorders, indicating the need to explore these plant species.

Asian Ancistrocladus Lianas as Creative Producers of Naphthylisoquinoline Alkaloids

This book describes a unique class of secondary metabolites, the mono- and dimeric naphthylisoquinoline alkaloids. They occur in lianas of the paleotropical Ancistrocladaceae and Dioncophyllaceae families, exclusively. Their unprecedented structures include stereogenic centers and rotationally hindered, and thus likewise stereogenic, axes. Extended recent investigations on six Ancistrocladus species from Asia, as reported in this review, shed light on their fascinating phytochemical productivity, with over 100 such intriguing natural products. This high chemodiversity arises from a likewise unique biosynthesis from acetate-malonate units, following a novel polyketidic pathway to plant-derived isoquinoline alkaloids. Some of the compounds show most promising antiparasitic activities. Likewise presented are strategies for the regio- and stereoselective total synthesis of the alkaloids, including the directed construction of the chiral axis.

Untargeted metabolomics study and identification of potential biomarkers in the six sections of the genus Stachys L. (Lamiaceae) using HPLC-MQ-API-MS/MS

INTRODUCTION

The genus Stachys L., belonging to the family Lamiaceae, is one of the largest genera with remarkable medicinal properties. Plants of this genus produce a broad range of secondary metabolites.

OBJECTIVES

Due to the incomplete comprehensive assessment of chemical profiles in Stachys species, we conducted an untargeted metabolomics study and identified potential biomarkers in the six sections of Stachys with chemotaxonomic importance.

MATERIAL AND METHODS

Dried leaves of 17 taxa were utilized for analysis of all the constituents using HPLC-MQ-API-MS. The obtained data were processed and analyzed using multivariate statistical methods, including heatmaps, PLS-DA score plots, functional analysis of metabolic pathways, metabolite set enrichment analysis, and biomarker and network analysis.

RESULTS

Among the 129 metabolites, 111 flavonoids and 18 non-flavonoids were recognized. The most represented flavonoids, including 41 flavones and 20 flavonols, displayed remarkable abundance. In non-flavonoid compounds, a total of six coumarins and six phenolic acids were present at high levels. In terms of approved markers in six sections, 76 chemical compounds, mainly flavonoids, coumarins, quinic acids, and cinnamic acids, were identified as potential biomarkers or chemotaxonomic indicators. Accordingly, the taxonomic complexities of some Stachys species in sections Fragilicaulis, Aucheriana, and Setifolia were properly resolved.

CONCLUSION

An HPLC-MS/MS-based metabolomics approach integrated with multivariate statistical methods was employed to identify (1) valuable markers and analyze metabolic diversity and (2) predict the pharmaceutical properties of Stachys species. The obtained chemical profiles provide a new perspective for investigation of the Stachys genus.

Design, Synthesis, and Antifungal Evaluation of Cryptolepine Derivatives against Phytopathogenic Fungi

Inspired by the widely antiphytopathogenic application of diversified derivatives from natural sources, cryptolepine and its derivatives were subsequently designed, synthesized, and evaluated for their antifungal activities against four agriculturally important fungi Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, and Sclerotinia sclerotiorum. The results obtained from in vitro assay indicated that compounds a1-a24 showed great fungicidal property against B. cinerea (EC₅₀ < 4 μg/mL); especially, a3 presented significantly prominent inhibitory activity with an EC₅₀ of 0.027 μg/mL. In the pursuit of further expanding the antifungal spectrum of cryptolepine, ring-opened compound f1 produced better activity with an EC₅₀ of 3.632 μg/mL against R. solani and an EC₅₀ of 5.599 μg/mL against F. graminearum. Furthermore, a3 was selected to be a candidate to investigate its preliminary antifungal mechanism to B. cinerea, revealing that not only spore germination was effectively inhibited and the normal physiological structure of mycelium was severely undermined but also detrimental reactive oxygen was obviously accumulated and the normal function of the nucleus was fairly disordered. Besides, in vivo curative experiment against B. cinerea found that the therapeutic action of a3 was comparable to that of the positive control azoxystrobin. These results suggested that compound a3 could be regarded as a novel and promising agent against B. cinerea for its valuable potency.

The potential of anti-malarial compounds derived from African medicinal plants: a review of pharmacological evaluations from 2013 to 2019

Background

African Traditional Medicine (ATM) is used for the healthcare of about 80% of the rural populations of the continent of Africa. The practices of ATM make use of plant-products, which are known to contain plant-based secondary metabolites or natural products (NPs), likely to play key roles in drug discovery, particularly as lead compounds. For various reasons, including resistance of strains of Plasmodium to known anti-malarial drugs, local African populations often resort to plant-based treatments and/or a combination of this and standard anti-malarial regimens. Emphasis has been laid in this review to present the anti-malarial virtue of the most recently published phytochemicals or natural products, which have been tested by in vitro and in vivo assays.

Methods

The data was based on the current version of the African Compound Libraries, which are constantly being updated based on inputs from journal articles and student theses (M.Sc/Ph.D) from African University libraries. Emphasis was laid on data published after 2012. In order to carry out the original data collection, currently being included in the African Compounds Database, individual journal websites were queried using the country names in Africa as search terms. Over 40,000 articles “hits” were originally retrieved, then reduced to about 9000 articles. The retained articles/theses was further queried with the search terms “malaria”, “malarial”, “plasmodium”, “plasmodial” and a combination of them, resulting in over 500 articles. Those including compounds with anti-malarial activities for which the measured activities fell within the established cut off values numbered 55, which were all cited in the review as relevant references.

Results and discussion

Pure compounds derived from African medicinal plants with demonstrated anti-malarial/antiplasmodial properties with activities ranging from “very active” to “weakly active” have been discussed. The majority of the 187 natural products were terpenoids (30%), followed by flavonoids (22%), alkaloids (19%) and quinones (15%), with each of the other compound classes being less than 5% of the entire compound collection. It was also observed that most of the plant species from which the compounds were identified were of the families Rubiaceae, Meliaceae and Asphodelaceae. The review is intended to continue laying the groundwork for an African-based anti-malarial drug discovery project.

Indole alkaloid from Nauclea latifolia promotes LDL uptake in HepG2 cells by inhibiting PCSK9

BACKGROUND

Proprotein convertase subtilisin/kexin type 9 (PCSK9) has been found to play a major role in atherosclerotic cardiovascular disease (ASCVD) by promoting hyperlipidemia. Its inhibition has therefore emerged as a viable drug target for improving the outcome of ASCVD. However, current monoclonal antibody PCSK9 inhibitors are considered cost ineffective and there is the need to discover new effective and cheaper small molecule alternatives.

PURPOSE

The methanolic and ethanolic crude extracts of Nauclea latifolia have been shown to possess anti-hyperlipidemic activity, but the chemical component(s) responsible for this activity and the mechanism of action have remained unknown. The objective of this study was therefore to identify N. latifolia constituents with anti-hyperlipidemic activity and to investigate the inhibition of PCSK9 as a probable mechanism of action.

METHOD

In the present study, compounds were isolated from the ethanolic extract of the stem of N. latifolia. The alkaloids were evaluated for their DiI-LDL uptake promoting activity in HepG2 cell. The most active compound was further assessed for its effect on low density lipoprotein receptor (LDLR) and PCSK9 protein expressions by western blot.

RESULTS

3R-3,14-dihydroangustoline (5), showed a relatively good activity in promoting LDL uptake (1.26-fold). It further increased LDLR protein expression and decreased the protein expression of PCSK9 in a dose dependent manner (1-50  µM).

CONCLUSION

Alkaloids from N. latifolia may serve as a source of new PCSK9 inhibitors.

LC-MS analysis of oils of Monodora myristica and Monodora tenuifolia and isolation of a novel cyclopropane fatty acid

Seeds of Monodora myristica and M. tenuifolia were extracted with hexane and the extracts were subjected to column chromatography, LC-MS and NMR analysis. In addition to masses of previously isolated compounds, other masses corresponding to unidentified compounds from the plants were detected. Using 2 D NMR techniques, one of the fractions from M. tenuifolia was characterised as a novel 13-(2-butylcyclopropyl)-6,9-dodecadienoic acid. However, none of the compounds detected in LC-MS corresponded to the ones previously identified by GC-MS.

Compounds from African Medicinal Plants with Activities Against Selected Parasitic Diseases: Schistosomiasis, Trypanosomiasis and Leishmaniasis

Parasitic diseases continue to represent a threat on a global scale, particularly among the poorest countries in the world. This is particularly because of the absence of vaccines, and in some cases, resistance against available drugs, currently being used for their treatment. In this review emphasis is laid on natural products and scaffolds from African medicinal plants (AMPs) for lead drug discovery and possible further development of drugs for the treatment of parasitic diseases. In the discussion, emphasis has been laid on alkaloids, terpenoids, quinones, flavonoids and narrower compound classes of compounds with micromolar range activities against Schistosoma, Trypanosoma and Leishmania species. In each subparagraph, emphasis is laid on the compound subclasses with most promising in vitro and/or in vivo activities of plant extracts and isolated compounds. Suggestions for future drug development from African medicinal plants have also been provided. This review covering 167 references, including 82 compounds, provides information published within two decades (1997-2017).

Jozilebomines A and B, Naphthylisoquinoline Dimers from the Congolese Liana Ancistrocladus ileboensis, with Antiausterity Activities against the PANC-1 Human Pancreatic Cancer Cell Line

Two new naphthylisoquinoline dimers, jozilebomines A (1a) and B (1b), were isolated from the roots of the Congolese plant Ancistrocladus ileboensis, along with the known dimer jozimine A₂ (2). These compounds are Dioncophyllaceae-type metabolites, i.e., lacking oxygen functions at C-6 and with an R-configuration at C-3 in their tetrahydroisoquinoline moieties. The dimers 1a and 1b consist of two 7,1'-coupled naphthylisoquinoline monomers linked through an unprecedented 3',6″-coupling in the binaphthalene core and not, as in 2, via the C-3-positions of the two naphthalene units. Thus, different from the C₂-symmetric jozimine A₂ (2), the new jozilebomines are constitutionally unsymmetric. The central biaryl axis of each of the three dimers is rotationally hindered, so that 1a, 1b, and 2 possess three consecutive chiral axes. The two jozilebomines have identical constitutions and the same absolute configurations at all four stereogenic centers, but differ from each other in their axial chirality. Their structural elucidation was achieved by HRESIMS, 1D and 2D NMR, oxidative degradation, and experimental and calculated ECD data. They exhibited distinct and specific antiplasmodial activities. All dimers showed potent cytotoxicity against HeLa human cervical cancer cells and preferential cytotoxicity against PANC-1 human pancreatic cancer cells under nutrition-deprived conditions. Furthermore, these dimers significantly inhibited the colony formation of PANC-1 cells, even when exposed to noncytotoxic concentration for a short time. Jozilebomines A (1a) and B (1b) and jozimine A₂ (2) represent novel potential candidates for future drug development against pancreatic cancer.

Nauclea latifolia: biological activity and alkaloid phytochemistry of a West African tree

Covering up to 2016Nauclea latifolia (syn. Sarcocephalus latifolius, Rubiaceae), commonly called the African pincushion tree, is a plant widely used in folk medicine in different regions of Africa for treating a variety of illnesses, including malaria, epilepsy and pain. N. latifolia has not only drawn the interest of traditional healers but also of phytochemists, who have identified a range of bioactive indole alkaloids in its tissue. More recently, following up on the traditional use of extracts in pain management, a bio-guided purification from the roots of the tree led to the identification of the active ingredient as tramadol, available as a synthetic analgesic since the 1970s. The discovery of this compound as a natural phytochemical was highlighted worldwide. This review focuses on the correlation between extracted compounds and pharmacological activities, paying special attention to infectious diseases and neurologically-related disorders. A critical analysis of the data reported so far on the natural origin of tramadol and its proposed biosynthesis is also presented.

The Chemistry and Biological Activities of Natural Products from Northern African Plant Families: From Taccaceae to Zygophyllaceae

Traditional medicinal practices have a profound influence on the daily lives of people living in developing countries, particularly in Africa, since the populations cannot generally afford the cost of Western medicines. We have undertaken to investigate the correlation between the uses of plants in Traditional African medicine and the biological activities of the derived natural products, with the aim to validate the use of traditional medicine in Northern African communities. The literature is covered for the period 1959-2015 and part III of this review series focuses on plant families with names beginning with letters T to Z. The authors have focused on curating data from journals in natural products and phytomedicine. Within each journal home page, a query search based on country name was conducted. All articles "hits" were then verified, one at a time, that the species was harvested within the Northern African geographical regions. The current data partly constitutes the bases for the development of the Northern African natural compounds database. The review discusses 284 plant-based natural compounds from 34 species and 11 families. It was observed that the ethnobotanical uses of less than 40 % of the plant species surveyed correlated with the bioactivities of compounds identified.

Amaryllidaceae and Sceletium alkaloids

The latest progress on the isolation, identification, biological activity and synthetic studies of the structurally diverse alkaloids from plants of family Amaryllidaceae has been summarized in this review.

The chemistry and bioactivity of Southern African flora I: a bioactivity versus ethnobotanical survey of alkaloid and terpenoid classes

As a whole, the African continent is highly endowed with a huge floral biodiversity.

The chemistry and bioactivity of Southern African flora II: flavonoids, quinones and minor compound classes

This review is intended to highlight the relevance of natural products in drug discovery paying particular attention to those derived from Southern African medicinal plants with diverse biological activities.

The chemistry and biological activities of natural products from Northern African plant families: from Ebenaceae to Solanaceae

Traditional medicinal practices significantly affect the livelihoods of populations in countries with developing economies.

The chemistry and biological activities of natural products from Northern African plant families: from Aloaceae to Cupressaceae

Traditional medicinal practices play a key role in health care systems in countries with developing economies.

The uniqueness and therapeutic value of natural products from West African medicinal plants, part II: terpenoids, geographical distribution and drug discovery

In this review series, an attempt has been made to give indepth coverage of natural products derived from West African medicinal plants with diverse biological activities.