Análise química e potencial bioativo do extrato aquoso de unha-de-gato (Uncaria tomentosa)

Abstract

This study investigated the chemical composition and biological activities of aqueous extracts obtained from the leaves and branches of Uncaria tomentosa (cat's claw), with emphasis on the influence of seasonality and the circadian cycle on the production of bioactive metabolites. The methodology included the collection of plant material in the municipality of Itacoatiara, Amazonas, Brazil, during different seasonal periods (rainy and dry seasons) and at three collection times (6:00 a.m., 12:00 p.m., and 6:00 p.m.), followed by drying, grinding, aqueous extraction by decoction, and freeze-drying. The study was organized into four chapters. The first chapter evaluated extract yield and showed that, during the rainy season, branches exhibited a higher average yield (6.52%) than leaves (2.33%), whereas during the dry season the opposite pattern was observed, with leaves presenting a higher average yield (6.65%) than branches (4.98%). A trend toward higher leaf yield at 6:00 p.m. during the dry season was also observed, suggesting an influence of the circadian cycle. The second chapter focused on the chemical characterization of the extracts using ¹H nuclear magnetic resonance (¹H NMR) spectroscopy, mass spectrometry, and phytochemical screening, allowing the identification of compounds such as chlorogenic acid, caffeine, and apigenin. Seasonal variations in the chemical profile were also investigated and found to be predominantly quantitative. The third chapter evaluated antioxidant activity using the DPPH and FRAP assays, demonstrating high free radical scavenging capacity and reducing power, with branch extracts exhibiting greater antioxidant activity than leaf extracts. The fourth chapter investigated antimicrobial activity using the agar diffusion (Cup Plate) method against Staphylococcus aureus, Bacillus cereus, and Escherichia coli, revealing predominant activity against Gram-positive bacteria, particularly in branch extracts collected during the dry season and daytime. It was concluded that seasonality, the circadian cycle, and the plant organ significantly influence the extraction yield, chemical composition, and antioxidant and antimicrobial activities of Uncaria tomentosa extracts.