Amaryllidaceae Alkaloids of Belladine-Type from Narcissus pseudonarcissus cv. Carlton as New Selective Inhibitors of Butyrylcholinesterase

Abstract

Thirteen known (1-12 and 16) and three previously undescribed Amaryllidaceae alkaloids of belladine structural type, named carltonine A-C (13-15), were isolated from bulbs of Narcissus pseudonarcissus cv. Carlton (Amaryllidaceae) by standard chromatographic methods. Compounds isolated in sufficient amounts, and not tested previously, were evaluated for their in vitro acetylcholinesterase (AChE; E.C. 3.1.1.7), butyrylcholinesterase (BuChE; E.C. 3.1.1.8) and prolyl oligopeptidase (POP; E.C. 3.4.21.26) inhibition activities. Significant human BuChE (hBUChE) inhibitory activity was demonstrated by newly described alkaloids carltonine A (13) and carltonine B (14) with IC₅₀ values of 913 ± 20 nM and 31 ± 1 nM, respectively. Both compounds displayed a selective inhibition pattern for hBuChE with an outstanding selectivity profile over AChE inhibition, higher than 100. The in vitro data were further supported by in silico studies of the active alkaloids 13 and 14 in the active site of hBuChE.

Keywords: Alzheimer’s disease; Amaryllidaceae; Narcissus pseudonarcissus cv. Carlton; alkaloids; butyrylcholinesterase; carltonine A–C; docking studies.

Figure 1

Structures of isolated alkaloids from Narcissus pseudonarcissus cv. Carlton.

Figure 2

Key 2D NMR correlations of compounds 13–15.

Figure 3

Structures of newly isolated (13 and 14) and recently reported belladine-type AAs 6-O-demethylbelladine and 4′-O-demethylbelladine [37].

Figure 4

The hBuChE active site in complex with (R)-13 (in salmon, A,B) and (S)-13 (in purple, C,D) pseudo-enantiomers. All the amino acids exhibiting in the vicinity of the ligands up-to 6.0 Å are rendered. Hydrogen atoms of amino acids are omitted for clarity. Catalytic triad residues are shown in yellow, and amino acid residues in blue (A,C). In 2D diagrams (B,D), crucial amino acid residues are displayed in different colours depending on the nature of the interaction (e.g., purple for π-π, orange for anion-π, dark green for van der Waals contact, and light green for conventional hydrogen bond).

Figure 5

hBuChE active site in complex with (R)-14 (in green, A,B) and (S)-14 (in light-blue, C,D) pseudo-enantiomers. All the amino acids exhibiting in the vicinity of the ligands up-to 6.0 Å are rendered. Hydrogen atoms of amino acids are omitted for clarity. Catalytic triad residues are shown in yellow and amino acid residues in blue (A,C). In 2D diagrams (B,D), crucial amino acid residues are displayed in different colours depending on the nature of the interaction (e.g., purple for π-π, orange for anion-π, dark green for van der Waals contact, light green for conventional hydrogen bond).