Avaliação fitoquímica e atividade biológica dos resíduos madeireiros de Sextonia rubra (Mez) van der Werff e Ocotea neesiana (Miq.) Kosterm

Abstract

The Brazilian Amazon harbors approximately 30% of all remaining tropical forests in the world. Despite this potential, studies of the woody parts regarding their chemical constituents and biological properties are scarce. In this context, seeking to add value to wood residues, this work aimed to conduct a phytochemical study of wood residues from Ocotea neesiana (Miq.) Kosterm. and Sextonia rubra (Mez) van der Werff and evaluate the biological activity of the isolated compounds. The methanol extracts obtained from O. neesiana and S. rubra were subjected to chromatographic fractionations in an open column with silica gel 60 (70-230 and 230-400 mesh), sephadexLH-20 and preparative thin-layer plate (silica gel 60). The purified compounds were identified/elucidated by nuclear magnetic resonance spectroscopy techniques (1D and 2D), high-resolution mass spectrometry (HRMS), gas chromatography coupled to mass spectrometry (GC-MS), and polarimetry. The most volatile fractions LAM-7, LAM-5.P2, and LAM-5.P4 of O. neesiana were also evaluated by GC-MS. The methanolic extract of O. neesiana resulted in the purification of the sesquiterpenes α cadinol (1), α-muurolol (3), T-cadinol (5), ent-T-muurolol (6), α-epi-cubenol (7), and the monoterpene α-terpineol (2), and the steroid β-sitosterol (4), in addition to the phenylpropanoids apiol (8) and dilapiol (9), as neolignans eusiderin A (10), rel (7S,8R,l’R,3’S,4’S)-4’-hydroxy-5,3’,5’-trimethoxy-3,4-methylenedioxy-2’-oxo-Δ1,3,5,5’,8’-8,1’,7,3’ (11),rel-(7S,8R,1’R,3’S,4’R)-4’-hydroxy-5,3’,5’-trimethoxy-3,4-methylenedioxy-2’-oxo-Δ1,3,5,5’,8’ -8,1’,7,3’-neolignan. (12), the diterpene 16-Methylsteritol A (13) (novel) and the flavonoid catechin (14). The methanolic extract of S. rubra was proven to isolate the phenalenone derivative sclerodine (15) and γ-lactones rubrenolide (16) and rubrinolide (17). To evaluate the biological potential, we performed antifungal assays of medical interest with compounds 10, 11, and 13 against strains of Candida albicans, C. krusei, Cryptococcus gattii, and C. neoformans. 16-Methylsteritol A (13) showed greater activity against C. gattii (MIC 40.6 µg/mL) and C. neoformans (MIC 81.2 µg/mL). For an antibacterial assay of agronomic relevance, the hexane and methanol extracts and the compounds in the mixture 16 and 17 of S. rubra, as well as compounds 1, 10, 11, and 13 of O. neeesiana, were tested against Xanthomonas citri subsp. citri. The results indicated a promising effect, with prevention below and equal to the positive control (CuSO4 250 µg/mL) for α-cadinol (1) (MIC and MBC of 50 µg/mL) and 16-Methylsteritol A (13) (MIC and MBC of 250 µg/mL). Thus, the study is contributing to the knowledge of Amazonian biodiversity and added value to wood waste.