Investigação fitoquímica das folhas de Onychopetalum periquino (ANNONACEAE)

Abstract

The Onychopetalum genus, belonging to the Annonaceae family, has only two species, O. amazonicum R.E. Fr and O. periquino (Rusbby) D.M. Johnson & N.A. Murray. These species are found mainly in the Amazon, in tropical forest regions. The species O. periquino is characterized by its medium to large trees that produce tasty fruits and flowers with a strong aroma. Previous phytochemical studies on this species have focused mainly on alkaloids and essential oils, leaving little explored its phenolic constituents, such as flavonoids. This gap suggests the need for complementary studies in order to explore the chemical potential of this species. Thus, the objective of the present work was to contribute to the phytochemical knowledge of the genus through the dereplication and isolation of substances from the aqueous extract of the leaves of O. periquino. To achieve this, the leaves of O. periquino were initially subjected to aqueous extraction. The aqueous extract was filtered through an open column containing Celite 545 and eluted with methanol. The methanol fraction was analyzed by DI-APCI-MS in data-dependent acquisition (DDA) mode with neutral loss scans for the identification of glycosylated flavonoids. A set of presumed glycosylated flavonoid isomers was analyzed by HPLC-APCI-MS/MS and dereplicated through manual interpretation of the MS/MS spectra. In parallel, the methanolic fraction underwent fractionation in an open column using Sephadex LH-20. Its subfractions were subjected to fractionation in semi-preparative HPLC using C18 and Phenylhexyl columns.. DI-APCI-MS analysis revealed the presence of isomers mainly derived from apigenin, luteolin, and quercetin, with 14 of them being successfully dereplicated through HPLC APCI-MS/MS analysis. On the other hand, chromatographic fractionation resulted in the isolation of 9 flavonoids: apigenin 8-C-neohesperidoside, apigenin 6-C-neohesperidoside, apigenin 7-O-rutinoside, luteolin 7-O-glucoside, vitexin, isovitexin, chrysoeriol 7-O glucoside, isoorientin and quercetin 3-O-rutinoside. All compounds were identified through spectroscopic/spectrometric data analysis (MS, MS/MS, 1D and 2D NMR) and comparison with literature data. The results revealed flavones and C- and O-glycosylated flavonols as the main classes of flavonoids present in the leaves of O. periquino. Although these classes have already been reported in the Annonaceae family, this is the first record in the Onychopetalum genus. This study also demonstrated the species O. periquino as a promising source of flavonoids.