Isolation of narciprimine from Cyrtanthus contractus (Amaryllidaceae) and evaluation of its acetylcholinesterase inhibitory activity

Ethnopharmacological relevance: Plants of the family Amaryllidaceae are used widely in traditional medicine in South Africa. Several of these, including representatives of the genus Cyrtanthus find use in the treatment of mental illness and age-related dementia. Aim of the study: Based on the distribution of central nervous system-activating alkaloidal constituents within the genus Cyrtanthus, Cyrtanthus contractus was here explored for such compounds which could interact with acetylcholinesterase (AChE), of significance in the progression of neurodegeneration associated with Alzheimer's disease. Materials and methods: The known phenanthridone alkaloid narciprimine was isolated via column chromatography of the ethanolic extract of bulbs of Cyrtanthus contractus. The structure of the compound was determined by high field 2D NMR and mass spectroscopic techniques. The classical method of Ellman et al. was used in the determination of AChE inhibitory activity. Results: The isolation of narciprimine from Cyrtanthus contractus is a landmark find since it has previously only been identified in Zephyranthes, Narcissus and Lycoris, genera endemic to the Americas. Europe and Asia, respectively. Narciprimine exhibited micromolar inhibitory activity (IC(50) 78.9) against the enzyme acetylcholinesterase. Conclusion: This work represents the first isolation of narciprimine from an African Amaryllidaceae species, which may be of chemotaxonomic significance. The AChE inhibitory activity of narciprimine, taken together with activities of other structurally similar inhibitors within the series affords further insight to the structural details of the lycorine alkaloid acetylcholinesterase inhibitory pharmacophore. (C) 2011 Elsevier Ireland Ltd. All rights reserved.