Composés azotés et autres constituants chimiques de trois plantes médicinales du Cameroun : Tabernaemontana contorta Stapf, Landolphia lucida K. Schum et Hedranthera barteri (Hook f.) Pichon (Apocynaceae) ; Evaluation des activités antibactérienne, antidi

Abstract

This work presents the phytochemical study of three Cameroonian medicinal plants of the Apocynaceae family, Tabernaemontana contorta, Landolphia lucida and Hedranthera barteri. Thus, the ethyl acetate fractions of the bark of the trunk of Tabernaemontana contorta, the lianas of Landolphia lucida and the alkaloid fraction of the stems of Hedranthera barteriled to the isolation and characterization of 29 compounds. The structural analysis of the isolated compounds was performed using 1D (1H and 13C) and 2D (COSY, HSCQC, HMBC and NOESY) nuclear magnetic resonance techniques, the most modern mass spectrometry, circular dichroism (CD) and by comparison with data from the literature. The ethyl acetate extract from the trunk bark of Tabernaemontana contorta has made it possible to isolate 12 compounds, including: three new derivatives of the cerebroside class (contortamide (64), tabernamide A (65) and tabernamide B (66)), as well as eight compounds already described in the literature, including four indole alkaloids (spegatrine (67), tombozine (68), Nb-methyl affinisine (69) and affinisine (70)) and five triterpenes (acid-2Į, 3Į, 23-trihydroxyursa-12, 20 (30)-dien-28 –oic (71), acid-2Į, 3ȕ, 23-trihydroxyursa-12, 5 (6)-dien-28-oic (72), bauerenol acetate (73), Į-amyrin (74), and betulinic acid (75)). The ethyl acetate extract from the lianas Landolphia lucida K. Schum. led to the isolation of 12 compounds including: four new derivatives including a pentacyclic triterpene (3-O-ȕ-(E)-(4'-O-acetylferuloyl)lupeol (77)), an anabolic steroid (methandriol dipropionate (78)), a lignan (2,3-bis (4'-hydroxy-3'-methoxy benzyl) dimethyl succinate (76)), a bicoumarin (7,7'-dimethoxy-6,6'-dicoumarinyl ether (80)); and eight known compounds namely a pentacyclic terpene (3ȕ-(E)-feruloyllupeol (79)), a phenolic acid (isovanollic acid (86)), a coumarin (scopoletin (81)), and flavonoids (rutin (20), quercitrin (82), quercetin (83), eriodictyol (84) and 3 ', 4', 5-trihydroxyflavone (85)). The enriched alkaloid fraction of the stems of Hedranthera barteri led to the isolation of five known alkaloids including: two indoles alkaloids (voacangine (2) and voacristine (4)), two bis indoles alkaloids (voacamine (62) and voacorine (88)), and a piperine (87) alkaloid. In order to corroborate their use in traditional medicine (prevention of bacteria growth and treatment of painful tumors), we have undertaken antibacterial (on Escherichia coli), antidiabetic and anticancer tests. Indeed, diabetes and the bacterial strain E. coli have been identified as potential risk factors for colorectal cancer promoting its development and metastasis. Thus, contortamide showed moderate anticancer activity against human colon cancer (Caco2) with a percentage inhibition of more than 60% compared to actinomycin D used as a reference. However, tabernamide A (65) (MIC = 1.4 µg/mL) and tabernamide B (66) (MIC = 1.8 µg/mL), (3-O-ȕ-(E)-(4-O-acetylferuloyl)lupeol (77) (MIC = 1.5 µg/mL) and 7,7'-dimethoxy-6,6'-dicoumarinyl ether (80) (MIC = 1.7 µg/mL) showed good antibacterial activity on the strain Escherichia coli (ATCC 25922) compared to ofloxacin (MIC = 50 µg/mL) used as a standard drug. However, 2,3-bis (4'-hydroxy-3'-methoxy-benzyl) dimethyl succinate (76) (IC50 = 525.55 ± 4.17 µM) and 3ȕ-(E)-feruloyllupeol (79) (IC50 = 452, 39 ± 2.10 µM) showed in vitro antiglycation activity compared to rutin (IC50 = 54.59 ± 2.20 µM) used as a standard, while 2,3-bis (4'-hydroxy-3'-methoxy-benzyl) dimethyl succinate (77) (IC50 = 268.06 ± 1.47 µM) also showed good inhibitory activity in vitro Į-glucosidase compared to the standard acarbose inhibitor (IC50 = 875.75 ± 2.08 µM). These antiglycation tests and Į-glucosidase thus highlighted the antidiabetic power of the two compounds.