Affinity Selection-Mass Spectrometry for the Identification of Ligands of Acetylcholinesterase from Topsentia ophiraphidites and Docking Studies for the Dereplicated Ligands.

Acetylcholinesterase (AChE) inhibition has been successful for the treatment of Alzheimer's disease and still stands as an important target in the search for novel ligands. In this context, affinity selection-mass spectrometry (AS-MS) has been acknowledged as a high-throughput screening (HTS) technique for large molecular libraries in drug discovery programs and natural product investigations. In this work, an AS-MS assay with AChE immobilized onto magnetic beads (AChE-MB) has been used to search for ligands in samples of the sponge Topsentia ophiraphidites collected in the archipelago of Fernando de Noronha, Brazil. Ligand dereplication disclosed 6-desmethyl-6-ethyl-9,10-dihydrospongosoritin A, 3,5-dibromo-O-methyltyrosine, 3-bromo-5-iodo-O-methyltyrosine, and 3,5-di-iodo-O-methyltyrosine as AChE ligands, which showed affinity ratios of 1.84, 1.34, 1.26, and 1.20, respectively, in the AS-MS assay. As a complementary approach, molecular docking analysis with human AChE has been carried out for the disclosed dereplicated ligands, in which the (R, R) stereoisomer of 6-desmethyl-6-ethyl-9,10-dihydrospongosoritin A stood out, performing important intermolecular interactions with the active sites of AChE, especially with the peripheral anionic site, at the entrance of the gorge. The results stimulate further investigations of these ligands in other pharmacological assays in order to better understand their mechanisms of action.