Targeted Isolation of Anti-Trypanosomal Naphthofuran-Quinone Compounds from the Mangrove Plant Avicennia lanata

Abstract

The discovery of new secondary metabolites from natural origins has become more challenging in natural products research. Different approaches have been applied to target the isolation of new bioactive metabolites from plant extracts. In this study, bioactive natural products were isolated from the crude organic extract of the mangrove plant Avicennia lanata collected from the east coast of Peninsular Malaysia in the Setiu Wetlands, Terengganu, using HRESI-LCMS-based metabolomics-guided isolation and fractionation. Isolation work on the crude extract A. lanata used high-throughput chromatographic techniques to give two new naphthofuranquinone derivatives, hydroxyavicenol C (1) and glycosemiquinone (2), along with the known compounds avicenol C (3), avicequinone C (4), glycoquinone (5), taraxerone (6), taraxerol (7), β-sitosterol (8) and stigmasterol (9). The elucidation and identification of the targeted bioactive compounds used 1D and 2D-NMR and mass spectrometry. Except for 6-9, all isolated naphthoquinone compounds (1-5) from the mangrove plant A. lanata showed significant anti-trypanosomal activity on Trypanosoma brucei brucei with MIC values of 3.12-12.5 μM. Preliminary cytotoxicity screening against normal prostate cells (PNT2A) was also performed. All compounds exhibited low cytotoxicity, with compounds 3 and 4 showing moderate cytotoxicity of 78.3% and 68.6% of the control values at 100 μg/mL, respectively.

Keywords: NMR; dereplication; high-throughput chromatographic; mangrove; mass spectrometry; metabolic profiling; multivariate analysis.

Figure 1

Total ion chromatogram of the crude extract of Avicennia lanata (blue and red lines represent positive and negative ionisation modes, respectively). Dereplication of numbered peaks is shown on Table 1. Boxed in green are the isolated compounds.

Figure 2

(A) Unsupervised Principal Component Analysis (PCA) scores plot of the A. lanata fractions showed moderate separation between the datasets; (B) OPLS-DA scores scatter plot of bioactive vs. inactive A. lanata fractions (R²(Y) = 1.00; Q² = 0.998); Q²(Y intercept); (C) Supervised OPLS-DA loadings plot showed the discriminating metabolites within the fractions and (D) OPLS-DA S-plot of bioactive vs. inactive A. lanata metabolites. Boxed in red are the isolated naphthofuranquinone compounds (1–5).

Figure 3

Compounds isolated from the mangrove plant Avicennia lanata.

Figure 4

Relative abundance of target metabolites (A–E) and isolated naphthofuranquinone derivatives in the bioactive fractions (F–J). Arrows indicate the occurrence of the other target metabolites in the segregated bioactive fraction F5 as shown in Figure 2B. Asterisk specifies the fraction from where the respective compounds were isolated. (A) P_3575: m/z = 321.133, RT = 11.66 min; (B) P_39: m/z = 465.177, RT = 18.89 min; (C) N_243: m/z = 455.353; RT = 26.74 min; (D) m/z = 810.601 [M + H], RT = 29.12 min; (E) m/z = 439.357 [M + H], RT = 26.82 min; (F) P_3632: hydroxyavicenol (1), m/z = 261.112, RT = 14.12 min; (G) P_3702: semiglycoquinone (2), m/z = 329.175, RT = 13.36 min; (H) P_10291: avicenol C (3), m/z = 289.107, RT = 11.62 min; (I) P_3663: avicequinone C (4), m/z = 257.081, RT = 9.74 min and (J) P_3684: glycoquinone (5), m/z = 329.175, RT = 16.06 min.

Figure 5

(A) Positive mode base peak chromatogram and mass spectrum and (B) COSY and HMBC correlations of compound 1.

Figure 6

(A) Positive mode base peak chromatogram and mass spectrum and (B) COSY and HMBC correlations of compound 2.