Chemical Constituents from the Vietnamese Mangrove Avicennia marina: Two New Iridoid Glycosides and Their Cytotoxicity Against Cancer Cell Lines

Abstract

Avicennia marina, commonly known as the grey mangrove, is a salt-tolerant species widely distributed in coastal and estuarine ecosystems. Traditionally, it has been used in folk medicine to treat skin diseases, rheumatism, and ulcers due to its anti-inflammatory and antimicrobial properties. However, comprehensive studies on the chemical constituents and their pharmacological effects remain limited. The dried powder of the aerial parts of A. marina (3.6 kg) was successfully extracted three times with methanol (20 L × 3, each for 2 h) using a multifunctional ultrasonic cleaner operated at 25 °C with a 50% amplitude setting. In this study, the methanolic extract of the aerial parts of A. marina led to the isolation of eight compounds, including two previously unreported iridoid glycosides-avicenosides A and B (1 and 2)-and six known compounds: techtochrysin (3), 7,4'-di-O-methyl-apigenin (4), luteolin (5), kaempferol (6), trans-caffeic acid (7), and 3,4-dihydroxybenzoic acid (8). Their chemical structures were elucidated using nuclear magnetic resonance (NMR) spectroscopy and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) and compared with previously published data. Moreover, the absolute configuration of the sugar moieties in the new compounds was also identified. All isolated compounds were evaluated for their cytotoxicity against HepG2 and A549 cancer cell lines. The results indicate potential cytotoxicity of the secondary metabolites from A. marina and provide evidence of their promising role as lead compounds for the development of novel anticancer agents.

Keywords: Avicennia marina; avicenosides A and B; cytotoxicity; iridoid glycoside; mangrove plant; secondary metabolite.

Figure 1

The isolated compounds (1–8) from A. marina included two previously unreported iridoid glycosides—avicenosides A and B (compounds 1 and 2, highlighted in red). Compounds 3–8 were identified as known compounds.

Figure 2

Key ¹H ¹³C HMBC interactions of compounds 1 and 2.

Figure 3

Key ROESY correlations of compounds 1 and 2. The energy-minimized 3D structures of 1 and 2 were generated using the MMFF force field in Maestro (Schrödinger; Maestro Version 12.5.139, MMshare Version 5.1.139, Release 2020-3; Windows-x64 platform).

Figure 4

Cytotoxicity of compound 6 and the positive control, ellipticine, tested in a dose-dependent manner in HepG2 and A549 cell lines. Data are presented as the mean ± SD of three independent experiments. ** p < 0.01 vs. control group; *** p < 0.0001 vs. control group.