A new indole alkaloid and anti-malarial activity of the stem bark extract of Chrysophyllum albidum

Background to the study: Chrysophyllum albidum stem bark extract had been shown to be antimalarial active in various studies but the compound responsible have not been identified.

Methods: Its stem bark ethanol extract was successively partitioned to obtain n-hexane, ethyl acetate, butanol fractions and the aqueous phase with the aim of isolating the antimalarial constituent(s). The fractions were all tested for chemosuppressive activities at doses 0-80 mg/kg using Peter’s four-day test in Plasmodium berghei berghei-infected mouse model with chloroquine (10 mg/kg) and normal saline as positive and negative control respectively

Result: The partitioned fractions: n hexane, butanol and aqueous with ED50 44.71±4.88, 54.84±4.25 and 54.42±3.84 and 56.6±4.64 respectively were comparable (p>0.05) in activity to each other. The ethyl acetate fraction with strong reactions to Dragendorff’s reagent and similarly has good weight, was further purified by repeated column chromatography leading to the isolation of a new indole alkaloid identified and characterized as 4, 5, 7, 8-tetrahydro-1H-1, 4-epoxyazepino [1′, 2′: 1, 2] pyrido [3, 4-b] indole-2, 3, 3(2H, 13H, 13bH)-triol (1) named as albidumine with a molecular formula C16H18N2O4. In addition, eleaginine (2), previously characterised from the seed was also identified in this stem-bark through LC-MS. To the best of our knowledge, compound 1 is a new alkaloidal constituent in Chrysophyllum sp. The structure was elucidated using the data from mass spectra, 1D (1H, 13C NMR and DEPT) and 2D-NMR (HMQC and HMBC) spectra.

Conclusion: A new indole alkaloid isolated from ethyl acetate fraction of the ethanol extract of the stem-bark of Chrysophyllum albidum and characterised as albidumine may likely be an antimalarial constituent of the plant