Ahmed Said Mohamed, Abdirahman Elmi, Fatouma Mohamed Abdoul-Latif, Rosella Spina, Imane Yamari, Maha AY Kordofani, Ali Mérito, Arnaud Risler, Dominique Laurain-Mattar and Samir Chtita

This study investigates the phytochemical composition and biological activities of crude extracts from Rhizophora mucronata Lam. collected in the Republic of Djibouti. Ethanolic extracts from leaves, stems, and flowers were analyzed, revealing high yields extractsusing 90% ethanol extraction. Flavonoid quantification showed the highest content in leaves (0.144 µg QE/mg extract), followed by flowers (0.059 µg QE/mg), and stems (0.041 µg QE/mg). HPLC-MS/MS analysis identified six major phytochemicals, including utin (C1), kaempferol derivatives (C2), flavone (C3), quinic acid (C4), 3-(benzoyloxy)-2-hydroxypropyl alpha-D-glucopyranosiduronic acid (C5), and naringin (C6). The flower extract exhibited the strongest antibacterial effect, particularly against Staphylococcus aureus (MIC = 640 µg/mL), whereas leave and stem extracts showed weaker activity (MIC > 2560 µg/mL for most Gram-negative bacteria). Antioxidant potential was evaluated using DPPH and ABTS assays, with flower extracts demonstrating the highest radical-scavenging activity (IC₅₀ = 159 µg/mL for DPPH and 137.5 µg/mL for ABTS). Furthermore, Molecular docking studies revealed strong binding interactions between naringin and key S. aureus proteins (binding energy -10.2 kcal/mol for 2W9G) and with the antioxidant enzyme catalase (2CAG, -11.1 kcal/mol), supporting its potential pharmacological relevance. ADMET analysis showed good solubility for all compounds, with C3 and C4 exhibiting the best bioavailability. Naringin displayed moderate toxicity (LD₅₀ = 2300 mg/kg). These findings suggest that Rhizophora mucronata extracts, particularly from flowers, could serve as promising natural sources of antibacterial and antioxidant agents.

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