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 μM
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-1β without affecting
anti-inflammatory signaling pathways.

丁酰胆碱酯酶（butyrylcholinesterase, BChE）的抑制作用，是治疗阿尔茨海默病（Alzheimer’s disease, AD）的新兴策略。2020年，研究人员分离得到3种此前未被报道的石蒜科生物碱（Amaryllidaceae alkaloids）——卡尔顿碱A~C（1~3），并报道了它们对BChE的抑制活性。本文首次报道了卡尔顿碱A~C（1~3）的非立体选择性全合成，并通过埃尔曼测定法（Ellman's assay）验证了其抑制活性：其中卡尔顿碱B（2）对BChE的抑制活性达到纳摩尔级别。进一步的动力学研究表明，卡尔顿碱B（2）是一种可逆竞争性BChE抑制剂。此外，研究团队采用小鼠海马神经细胞开展表型筛选，对外消旋卡尔顿碱B（2）进行了评价，结果显示其在5~10 μM浓度范围内，可对抗谷氨酸诱导的氧化性细胞死亡与铁死亡，同时可缓解碘乙酸诱导的ATP耗竭。最后，在脂多糖激活的小胶质细胞N9株实验中，卡尔顿碱B（2）展现出免疫调节作用：可下调诱导型一氧化氮合酶（NOS2）、白细胞介素1β（IL-1β）等促炎标志物的表达，且不会影响抗炎信号通路。