Search

ABSTRACT: Background: Across West Africa, Tabernaemontana crassa Benth., Voacanga africana Stapf., and Rauvolfia vomitoria Azfel. (Apocynaceae) share the same local names, a situation that puts them at risk of unintended adulteration. The study aimed at setting macro- and micromorphological standards, phytochemical and physicochemical standards for the unequivocal differentiation of the three plants. Methods: Macro- and micro-morphological features, quantitative microscopy, soluble extractives, pH, ash values, fluorescence, phytochemical and thin layer chromatographic profiles of leaves, stem, and roots of the three plants were determined using standard methods. Results: The whole leaves showed that all three plants possessed opposite petiolate leaves. The leaves of R. vomitoria and V. africana were elliptic in /shape, whereas T. crassa leaves were oblanceolate. Further differences in stomata arrangement, epidermal cells, histological features of their midribs, surface data determinations, phytochemical and physicochemical profiles of the leaves, stem bark and roots present useful data for clearly distinguishing between the three species. Conclusion: The determined parameters of the leaves, stems, and roots of T. crassa, V. africana, and R. vomitoria support the unequivocal identification of the individual plants. This is important for correct sourcing of these plants for herbal product manufacturers, regulators, and researchers.

The introduction of glucagon-like peptide 1 (GLP-1)-based therapies has greatly improved the management of type 2 diabetes (T2D), as they ensure good blood glucose control and promote weight loss. Ingestion of standardized herbal remedies that promote the same endogenous metabolic processes affected by the GLP-1-based treatments could provide cheaper alternatives in low- and middle-income countries, where there is currently an increase in the incidence of T2D. The focus in this study was to determine quality control parameters and the prime factors for the Rauvolfia-Citrus tea (RC-tea), as used in Nigerian traditional medicine to treat T2D. We have previously shown that the RC-tea that is made by boiling leaves of Rauvolfia vomitoria Afzel. and fruits of Citrus aurantium L. causes normalization of blood glucose and reduction of ectopic lipid accumulation in genetic diabetic (BKS-db) mice and in humans with T2D. The standardized RC-tea was made by boiling 40 g dried R. vomitoria foliage and 200 g fresh C. aurantium fruits per litre. The resulting golden-brown extract is free of microbial contamination, has pH 5 and contains ca. 230 mg naringin (marker compound for C. aurantium) and 25 mg robinin (marker compound for R. vomitoria) per litre. In addition, the herbal extract has the characteristic HPLC-DAD fingerprint where the marker compounds, naringin and robinin have retention times of approximately 26.3 min and 26.9 min, respectively, when using the outlined column and gradient elution conditions. Comparative evaluations of the antidiabetic effects of the standardized RC-tea and boiling water-extracts made with C. aurantium fruits alone (CA), R. vomitoria foliage alone (RV) and a combination of CA and RV, (CA + RV) in BKS-db mice, indicate that components from R. vomitoria foliage drive the reductions in ectopic lipid accumulation, since CA-treated mice lacked this effect. However, the normalization of blood glucose arises from combination of components from the two source plant materials as administration of either CA or RV resulted in hypoglycaemia. Interestingly, treatment with the CA + RV mixture, generated by mixing individually produced CA and RV plant extracts, resulted in hyperglycaemia, possibly due to drug-drug interactions of the blood glucose-reducing components in either plant extract. Hence, our data show that the best antidiabetic outcome results from the traditional practice of boiling R. vomitoria foliage and C. aurantium fruits together., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Five new peraksine derivatives rauvomine C-G (1-5) along with four known analogues (6-9) were isolated from the stems of Rauvolfia vomitoria Afzel. (Apocynaceae). Structural determinations of the new monoterpene indole alkaloids were elucidated via comprehensive spectroscopic analyses and ECD calculations. Rauvomine C (1) with an unprecedented framework type represents the first example of C 18 peraksine-type nor-monoterpene indole alkaloid featuring a chlorine atom at C-16 and its plausible biosynthetic pathway was also proposed. All the isolates were evaluated for their anti-inflammatory, cytotoxic, and acetylcholinesterase inhibitory activities. Among them, the new framework alkaloid rauvomine C (1) showed significant anti-inflammatory activities on NO production in LPS-induced RAW264.7 mouse macrophages with IC 50 value of 10.76 μM. Additionally, peraksine-type alkaloids featuring pyran ring (5, 8, and 9) exhibited potential anti-inflammatory activities with IC 50 values ranging from 17.52 to 20.99 μM., Competing Interests: Declaration of Competing Interest The authors declared that they have no conflicts of interest to this work., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Seventeen monoterpene indole alkaloids, including seven new alkaloids (1-7) and ten known analogues (8-17), were isolated and identified from the leaves of R. vomitoria. The structures of new alkaloids were elucidated by extensive spectroscopic analysis and single-crystal X-ray diffraction analysis. Rauvomitorine I (1) represents the first example of an unprecedented C 22 yohimbine-type monoterpene indole alkaloid featuring a carboxymethyl at C-14. The exceedingly rare vobasenal (2-3) and affinisine oxindole (5-6) framework type alkaloids are first reported from the Rauvolfia genus. Most notably, the structure of vobasenal-type alkaloids (2-3) were first determined by single-crystal X-ray diffraction analyses. Alkaloids 1-17 were tested their cytotoxicity against five cancer cell lines, however, none of them showed significant cytotoxicity at a concentration of 40 μM. All the isolated alkaloids were evaluated their acetylcholinesterase (AChE) inhibitory activities. Alkaloid 3 exhibited significant anti-AChE activity with an IC 50 value of 16.39 ± 1.41 μM and alkaloids 8 and 10 showed moderate anti-AChE activities whereas the others (2, 9, 13, and 17) were weak inhibitors. This is the first report of vobasenal-type alkaloids as AChE inhibitors, indicating this type of alkaloids may be important sources for the discovery of new AChE inhibitors. A preliminary structure-activity relationship for AChE inhibitory activities showed the presence of the N-methyl group in vobasenal-type alkaloids may be essential for anti-AChE activity. Further molecular docking studies of vobasenal-type alkaloids revealed that interaction with Trp133 and Trp86 residues at hydrophobic subsite are necessary for the AChE inhibitory activities. This study not only enriches the chemical diversity of alkaloids in Apocynaceae plants but also provides new potential leading compounds and versatile scaffolds for the design and development of new AChE inhibitors to treat AD., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)