Triterpene saponins of Maesa lanceolata stem wood

Abstract

Phytochemical analysis of aqueous MeOH extract of Maesa lanceolata stem wood has led to the isolation of four new triterpene saponins characterized as 16α,21β-diacetoxy-22α-angeloyl-28-hydroxyolean-12-ene 3-O-[α-rhamnopyranosyl-(1″″ → 6‴)-β-glucopyranosyl-(1‴ → 3′)][β-glucopyranosyl-(1″ → 2′)]-β-glucuronopyranoside (1), 16α-acetoxy-21β-hydroxy-22α-angeloyl-13β,28-oxydoolean-28α-ol 3-O-[α-rhamnopyranosyl-(1″″ → 6‴)-β-glucopyranosyl-(1‴ → 4′)][β-glucopyranosyl-(1″ → 2′)]-α-arabinopyranoside (2), 16α-acetoxy-21β,22α-diangeloyl-13β,28-epoxyoleanane 3-O-[α-rhamnopyranosyl-(1″″ → 6‴)-β-glucopyranosyl-(1‴ → 4′)][β-glucopyranosyl-(1″ → 2′)]-β-xylopyranoside (3), and 16α,22α-diacetoxy-13β,28-oxydoolean-28α-ol 3-O-[β-glucopyranosyl-(1″ → 2′)][β-glucopyranosyl-(1‴ → 3′)]-β-glucuronopyranoside (4), together with the known compounds β-acetylamyrin, physcion, emodin, chrysophanol, ursolic acid, 16α-hydroxy-12-oleanene 3-O-glucoside, β-amyrin, sitosterol 3-O-β-glucoside, stigmasterol, and 3β,28-dihydroxyolean-12-ene. Their structural elucidation was accomplished by homo- and heteronuclear 2D NMR technique as well as comparison with data from known compounds. The in vitro antibacterial activity of the aqueous MeOH extract was also investigated and zones of inhibition ranging from 32 ± 1.1 to 14 ± 0.2 mm were observed. Among the isolates, compound 1 was the most active with an minimum inhibitory concentration value of 25 μg/ml against Staphylococcus aureus.

Keywords:

• Maesa lanceolata
• Myrsinaceae
• oleanane-type triterpene saponins
• antibacterial activity
• stem wood

Acknowledgements

The authors are thankful to Kenya Medical Research Institute (KEMRI), Kisumu, Kenya for the use of their laboratory to perform the biological activity tests. Mr Mutiso of Botany Department, Nairobi University is highly thanked for identification of the plant. Dr Odada of Kenya Medical Research Institute (KEMRI) is acknowledged for the identification of the bacteria. TWAS-CAS is acknowledged for giving LOAM fellowship to China where part of this work was done. Alexander von Humboldt Foundation is also thanked for awarding fellowship to LAOM to undertake analysis in Germany.