The African cherry: A review of the botany, traditional uses, phytochemistry, and biological activities of Prunus africana (Hook.f.) Kalkman.

ETHNOPHARMACOLOGICAL RELEVANCE: Prunus africana (Hook.f.) Kalkman (Rosaceae), commonly known as "Pygeum" or "African cherry", occurs in mainland montane forests scattered across sub-Saharan Africa, Madagascar, and some surrounding islands. Traditionally, decoctions of the stem-bark are taken orally for the treatment of a wide variety of conditions, such as benign prostatic hyperplasia (BPH), stomach ache, chest pain, malaria, heart conditions, and gonorrhoea, as well as urinary and kidney diseases. The timber is used to make axe handles and for other household needs. The dense wood is also sawn for timber. AIM: The fragmented information available on the ethnobotany, phytochemistry, and biological activities of the medicinally important P. africana was collated, organised, and analysed in this review, to highlight knowledge voids that can be addressed through future research. MATERIALS AND METHODS: A bibliometric analysis of research output on P. africana was conducted on literature retrieved, using the Scopus® database. The trend in the publications over time was assessed and a network analysis of collaborations between countries and authors was carried out. Furthermore, a detailed review of the literature over the period 1971 to 2021, acquired through Scopus, ScienceDirect, SciFinder, Pubmed, Scirp, DOAJ and Google Scholar, was conducted. All relevant abstracts, full-text articles and various book chapters on the botanical and ethnopharmacological aspects of P. africana, written in English and German, were consulted. RESULTS: A total of 455 documents published from 1971 to 2021, were retrieved using the Scopus search. Analysis of the data showed that the majority of these documents were original research articles, followed by reviews and lastly a miscellaneous group comprising conference papers, book chapters, short surveys, editorials and letters. Data were analysed for annual output and areas of intense research focus, and countries with high research output, productive institutions and authors, and collaborative networks were identified. Prunus africana is reported to exhibit anti-inflammatory, analgesic, antimicrobial, anti-oxidant, antiviral, antimutagenic, anti-asthmatic, anti-androgenic, antiproliferative and apoptotic activities amongst others. Phytosterols and other secondary metabolites such as phenols, triterpenes, fatty acids, and linear alcohols have been the focus of phytochemical investigations. The biological activity has largely been ascribed to the phytosterols (mainly 3-ß-sitosterol, 3-ß-sitostenone, and 3-ß-sitosterol-glucoside), which inhibit the production of prostaglandins in the prostate, thereby suppressing the inflammatory symptoms associated with BPH and chronic prostatitis. CONCLUSIONS: Many of the ethnobotanical assertions for the biological activity of P. africana have been confirmed through in vitro and in vivo studies. However, a disparity exists between the biological activity of the whole extract and that of single compounds isolated from the extract, which were reported to be less effective. This finding suggests that a different approach to biological activity studies should be encouraged that takes all secondary metabolites present into consideration. A robust technique, such as multivariate biochemometric data analysis, which allows for a holistic intervention to study the biological activity of a species is suggested. Furthermore, there is a need to develop rapid and efficient quality control methods for both raw materials and products to replace the time-consuming and laborious methods currently in use.

A review of biological activities and phytochemistry of six ethnomedicinally important South African Croton species.

ETHNOPHARMACOLOGICAL RELEVANCE: The genus Croton (Euphorbiaceae) encompasses 1300 species, which consist of a variety of trees and shrubs distributed across the world. About 26 species are harboured on the African continent. This genus plays an essential role in African folk medicine. Croton species are traditionally used for the treatment of many diverse conditions such as diabetes, malaria, sexually transmitted diseases, cancer, inflammation, fever, digestive problems and fungal infections. AIM OF THE REVIEW: To provide a comprehensive overview of the ethnobotany, traditional uses, phytochemistry and biological activities of six selected southern Africa Croton species; C.gratissimus Burch., C. megalobotrys Müll.-Arg., C. menyhartii Gȕrke, C. pseudopulchellus Pax, C. steenkampianus Gerstner and C. sylvaticus Schltdl.). MATERIALS AND METHODS: Various electronic databases, namely Google, Google Scholar, Scopus, ScienceDirect, Biomed Central and Pubmed, were used to search for information related to the traditional uses, chemistry and pharmacology of Croton species. Books were also consulted to collect all pertinent information. RESULTS AND DISCUSSION: The ethnopharmacology, phytochemistry and biological activities of southern African Croton species are reviewed. The literature revealed that Croton species are trusted traditional medicines for the treatment of microbial infections and malaria. The non-volatile components of Croton species include flavonoids, terpenoids and alkaloids, while the volatile constituents comprise mainly of monoterpenes (α-phellandrene, α-pinene and 1,8-cineole) and sesquiterpenes (caryophyllene oxide). Most of the reported biological activities (anti-oxidant, antimicrobial, anticancer and antimalarial) were based on in vitro assays and were accredited to various extracts. However, both in vitro and in vivo studies, linking the reported activities to specific compounds, are still lacking. CONCLUSIONS: Croton species are used in traditional medicine to treat a range of ailments, and various in vitro biological activities have been investigated, with some extracts exhibiting good activity that could be considered for further investigation. The in vitro activities obtained seem to justify the use of Croton species in traditional medicine. Data on in vivo studies are scarce and studies usually focused on a single collection. The need to establish a quality control protocols for the standardisation of these herbal drugs is also important.

Mesembrine: The archetypal psycho-active Sceletium alkaloid.

(-)-Mesembrine is a chiral alkaloid that features an aryloctahydroindole skeleton and is most commonly found in species of the succulent genus Sceletium. Several Sceletium species are used by various ethnic groups in South Africa to manage disorders of the central nervous system. Binding assays have revealed that mesembrine is a more potent inhibitor of the serotonin transporter (SERT) than fluoxetine (Prozac) which has prompted the commercialization of mesembrine-containing consumer products. The congested all carbon quaternary stereocenter present at the bridgehead of mesembrine has rendered it a compound of interest for research in synthetic chemistry, which has assisted in the absolute configuration of the naturally occurring isomer to be assigned. Accordingly, this review will cover the recent literature pertaining to the distribution, structural elucidation, chemotaxonomy, biosynthesis, organic synthesis, as well as the biological activities of (-)-mesembrine. Recent synthetic procedures of the non-natural enantiomer as well as the racemate are also considered.

Isolation and Characterization of Sclerienone C from Scleria striatinux.

Herein, we report the isolation and characterization of sclerienone C, a novel sesquiterpene isolated from the methylene chloride/methanol (1:1) extract of Scleria striatinux that we have deduced to have structure 1. This medicinal spice of Cameroon has been shown to display antimicrobial and antiplasmodial activities. The isolation and purification involved a combination of methods including silica gel column chromatography, Sephadex LH-20, and semi-prep HPLC separations. Structure elucidation was carried-out by means of spectroscopic analysis and comparison with previously isolated sesquiterpene derivatives from the plant.

Preparation and antimalarial activity of a novel class of carbohydrate-derived, fused thiochromans.

A novel class of fused thiochroman derivatives has been prepared by an efficient and versatile synthetic procedure involving nucleophilic displacement of the side-chain iodo substituent in 2-deoxy-2-C-iodomethyl glucosides by thiophenolate ions, and subsequent intramolecular C-glycoside formation. A range of aromatic substituents is tolerated, and the subsequent facile selective oxidation of the sulfur to the sulfoxide or sulfone level expands the range and molecular diversity of the series of compounds. A selection of the sulfoxide and sulfone derivatives bearing lipophilic substituents on the aromatic portion were found to have antimalarial activities in the low micromolar range.

Regiospecific synthesis of 2-halo-3-(2'-glucalyl)benzo[b]thiophenes.

A regiospecific synthetic strategy for the synthesis of 2-chloro-3-substituted benzo[b]thiophenes is developed via a dichlorocarbene insertion and sigmatropic rearrangement of an in situ generated ylide. The current protocol provides a reversed regiochemistry to the commonly employed electrophilic cyclization reaction for the synthesis of benzo[b]thiophenes and access to their hitherto under-represented chlorinated derivatives.

Stereoselective synthesis of thiochromenes via intramolecular tandem thio-Michael addition of in situ generated α,ß-unsaturated aldehydes.

An efficient and highly stereoselective strategy for the synthesis of 2,3-substituted thiochromenes having a complex and easily transformable group at the stereogenic center has been developed via a tandem thio-Michael addition reaction of an in situ generated α,ß-unsaturated aldehyde sugar derivative. The protocol is superior to reported protocols in that the carbohydrate-derived substituent at the stereogenic center of the thiochromene is versatile and is amenable for further transformation.

1-O-Acetyl-3,4,6-tri-O-benzyl-2-C-bromo-methyl-2-de-oxy-α-d-glucopyran-ose.

In the title compound, C30H33BrO6, the pyran-ose ring adopts a chair conformation. Two of the O-benzyl phenyl rings lie almost perpendicular to C/C/C/O plane formed by the ring atoms not attached to these O-benzyl phenyl rings, and form dihedral angles of 85.1 (2) and 64.6 (2)°, while the third O-benzyl phenyl ring is twisted so that it makes a dihedral angle 34.9 (2)° to this C/C/C/O plane. This twist is ascribed to the formation of an S(8) loop stabilized by a weak intra-molecular C-H⋯O hydrogen bond.

3,4,6-Tri-O-acetyl-1,2-[(S)-ethyl-idene]-ß-d-mannopyran-ose.

In the title compound, C(14)H(20)O(9), the six-membered pyran and the five-membered dioxalane rings adopt chair and twisted conformations, respectively. In the crystal, the mol-ecules are linked by C-H⋯O inter-actions.

Occurrence of sesquiterpene derivatives in Scleria striatonux de wild (Cyperaceae).

Scleria striatonux (Cyperaceae), a spice traditionally used in Cameroon, displayed an antiplasmodial activity. Two new sesquiterpenes, 1 (sclerienone A) and 2 (sclerienone B), have subsequently been isolated from the methylene chloride/methanol extract of the rhizome. Their separation involved a combination of methods including repeated silica gel open column chromatography, Sephadex LH-20 and semi-preparative HPLC. Structure elucidation was achieved by means of chemical tests and extensive spectral studies.

Okundoperoxide, a bicyclic cyclofarnesylsesquiterpene endoperoxide from Scleria striatinux with antiplasmodial activity.

Okundoperoxide (1) was isolated by bioassay-guided fractionation of extracts from Scleria striatinux (syn. S. striatonux). The compound contains a cyclic endoperoxide structural moiety and possesses moderate antimalarial activity.