Total Syntheses of the Amaryllidaceae Alkaloids Carltonines A-C and the Neuroprotective and Immunomodulatory Evaluation of Carltonine B

The inhibition of butyrylcholinesterase (BChE) represents an emerging approach for the treatment of Alzheimer's disease (AD). In 2020, three previously undescribed Amaryllidaceae alkaloids, carltonines A-C (1-3), were isolated, and their inhibitory activity on BChE was reported. Herein, we describe the first, nonstereoselective total synthesis of carltonine A-C (1-3) and confirmed their inhibitory activity using Ellman's assay, with nanomolar BChE inhibition by carltonine B (2). Further kinetic studies revealed that carltonine B (2) acts as a reversible, competitive inhibitor of BChE. In addition, racemic carltonine B (2) was evaluated in a phenotypic screening using murine hippocampal nerve cells, where it demonstrated protective effects against glutamate-induced oxytosis and ferroptosis at concentrations ranging from 5 to 10 mu M and against iodoacetic acid-induced ATP depletion. Finally, in studies using lipopolysaccharide-activated microglial N9 cells, carltonine B (2) exhibited immunomodulatory effects by downregulating pro-inflammatory markers such as NOS2 and IL-1 beta without affecting anti-inflammatory signaling pathways.