Prospecção de inibidores da enzima acetilcolinesterase (AChE) em espécies do gênero onychopetalum (Annonaceae) para o tratamento da doença de Alzheimer

Abstract

Onychopetalum is a Neotropical genus botanically close to the Unonopsis genus, whose species are used in traditional medicine to treating neurodegenerative disease, such as Alzheimer's disease (AD). Phytochemical studies point to Unonopsis as a promising source of alkaloids, substances previously reported as potential inhibitors of the enzyme acetylcholinesterase (AChEIs), while the alkaloid composition of Onychopetalum remains almost unexplored. The acetylcholinesterase enzyme (AChE) remains a highly viable target for the symptomatic improvement of AD, and is currently the main strategies for the treatment of this disease. Therefore, the objective of the present work was to prospect potential AChEIs in leaves of the species O. amazonicum and O. periquino through the integration of mass spectrometry (MS) based analysis, molecular docking studies, semisynthetic modifications and pharmacological assays by capillary enzyme reactor (ICER). The MS based analysis allowed the tentative identification of aporphine, benzyltetrahydroisoquinoline, oxoaporphine and tetrahydroprotoberberine alkaloids on the leaves of both species, tetrahydroprotoberberine being observed as major constituents in the leaves of O. amazonicum. Docking analysis based on the crystal structure of Torpedo californica AChE (TcAChE) suggested moderate activity for the dereplicated substances, while the planned benzylated derivatives were described as highly active, indicating that π-type and charge-based interactions may be determinant for increasing the inhibition potential against AChE enzyme, and highlighted the N-benzylated derivatives as potential AChEIs. Semisynthesis procedures from stepholidine and isocorypalmine alkaloids allowed the obtention of benzyltetrahydroprotoperberines derivatives (-)-(7S, 13aS) -7-benzylstepholidine, (-)-(7R,13aS)-7-benzylstepholidine, (-)-(S)-2-O-benzylstepholidine, (-)-(S)-10-O-benzylstepholidine, (-)-(S)-2-O-benzylisocorypalmine, (-)-(S)-2-O-benzylstepholidine and (-)-(S)-O-O-dibenzylstepholidine, being the alkaloids (-)-(7S, 13aS)-7-benzylstepholidine, (-)-(7R,13aS)-7-benzylstepholidine and (-)-(S)-10-O-benzylstepholidine, described for the first time in the literature. The ICER assays showed inhibition percentages varying between 35.22-90.49% for the tested substances, with benzylated derivatives presenting better results than their precursors. These observations, along with the key interactions highlighted in molecular docking analysis, may be helpful in designing new AChEIs. Overall, the proposed approach demonstrated the usefulness of stepholidine alkaloid as a suitable model for the rational design of AChEIs, therefore, these results can be useful in the development of new drugs for the treatment of Alzheimer's disease.