Anacyphrethines A and B as potent analgesics: Multiple ion channel inhibitors with an unprecedented chemical architecture
Hui Chen, Hanqi Zhang, Chao Niu, Bianlin Wang, Biao Gao, Zhijun Liu, Guangmin Yao, Haji Akber Aisa
Abstract
Multi-target analgesics with minimal side effects and high efficacy are a key research focus in addressing the global pain crisis. Using a molecular networking approach, five pairs of potent analgesic alkaloid enantiomers were isolated from the roots of Anacyclus pyrethrum ( A . pyrethrum ). Their structures were elucidated by comprehensive spectroscopic data analysis, including LR-HSQMBC and 1 H- 15 N HMBC, quantum 13 C NMR DP4+ and ECD calculations, and single-crystal X-ray diffraction analysis. Anacyphrethines A ( 1 ) and B ( 2 ) are highly conjugated and polymethylated 6/6/6/6/5/7/5/5-fused octacyclic tetraazabic alkaloids possessing an unprecedented 8,14,18,24-tetraaza-octacyclo[16.8.2.1 1,23 .0 4,28 .0 5,17 .0 9,16 .0 11,15 .0 21,27 ] nonacosane motif. Their biosynthetic pathways are proposed involving key aldol, hydroamination, and Schiff base reactions. All isolates showed potent analgesic effects in vivo . Even at a lower dose of 0.2 mg/kg, (±)- 1 and (+)- 1 still exhibited more potent analgesic activities than morphine. Interestingly, the racemic mixture (±)- 1 showed stronger analgesic effect than either pure enantiomer alone at higher doses of 5 and 1 mg/kg; while, (±)- 1 showed significant analgesic activities comparable to (+)- 1 at lower doses of 0.2 and 0.04 mg/kg. (+)- 1 had stronger analgesic effect than (−)- 1 at five tested does. Further tests on 44 analgesic-related targets demonstrated that (+)- 1 showed significant inhibitory effects against many ion channels such as TRPM8, Kv1.2, Kv1.3, and Ca v 2.1 with IC 50 values of 1.10±0.26, 4.20±0.07, 2.20±0.24, and 10.40±0.69 μmol/L, respectively, while (−)- 1 primarily inhibited TRPC6, Kv1.2, and Kv1.3 ion channels with IC 50 values of 0.81±0.05, 0.91±0.04, and 1.50±0.13 μmol/L, respectively, without affecting the opioid receptors, suggesting their non-opioid analgesic potentials. The molecular dockings provided structural guidance to develop potent non-opioid analgesics.