Abstract
Phytochemical investigation of the leaves of Guatteria friesiana (Annonaceae) afforded three new isoquinoline alkaloids, 13-hydroxy-discretinine, 6,6a-dehydroguatteriopsiscine and 9-dehydroxy-1-methoxy-dihydroguattouregidine. Eight known alkaloids were also isolated, 13-hydroxy-2,3,9,10-tetramethoxyprotoberberine, guatteriopsiscine, lysicamine, liriodenine, atherospermidine, lanuginosine, 7,8-dihydro-8-hydroxypalmatine and palmatine. 13-Hydroxy-2,3,9,10-tetramethoxyprotoberberine was only obtained by synthesis and is being reported as a natural product for the first time. The structures of the isolated alkaloids were established by extensive analysis of 1D and 2D nuclear magnetic resonance (NMR) and mass spectrometric (MS) data, as well as by comparison with data reported in the literature. The in vitro cytotoxic activity of the major alkaloids was evaluated against tumor and non-tumor cell lines. All of the alkaloids evaluated were determined to be inactive based on National Cancer Institute (NCI/USA) criteria. However, the alkaloid palmatine exhibited a cytostatic effect on MCF-7 (breast) and U251 (glioma) human tumor cell lines, with GI50 values lower than 20.0 µmol L-1 (10.5 and 16.2 µmol L-1, respectively), suggesting a selective cytotoxic action.
Highlights
Previous phytochemical and pharmacological investigations on some Guatteria species revealed the presence of bioactive compounds, including cytotoxicity against human tumor cell lines,4-6 as well as antimicrobial,4,5,7-10 antioxidant7 and antiparasitic activity against Leishmania sp.,11,12 Plasmodium falciparum12 and Trypanosoma cruzi
Compound 1 was isolated as a yellowish amorphous powder, optically active, [a]D25 –169.95o (c 0.2, CHCl3), with the molecular formula C20H23NO5, as determined by HRESIMS and nuclear magnetic resonance (NMR)
The structure of compound 1 was fully established by HSQC, HMBC and 1D nuclear Overhauser effect (NOE) NMR experiments (Table 1)
Summary
The genus Guatteria (Ruiz & Pav.) is the largest in the family Annonaceae and comprises approximately 210 recognized species, distributed exclusively in the Neotropical regions ( not in Argentina and Paraguay).1,2 Some species of this genus are known for their aromatic fragrances and their medicinal properties.3 Previous phytochemical and pharmacological investigations on some Guatteria species revealed the presence of bioactive compounds, including cytotoxicity against human tumor cell lines,4-6 as well as antimicrobial,4,5,7-10 antioxidant7 and antiparasitic activity against Leishmania sp.,11,12 Plasmodium falciparum12 and Trypanosoma cruzi.12 These bioactivities are attributed to the presence of terpenes and alkaloids in these plant species. Compound 1 was isolated as a yellowish amorphous powder, optically active, [a]D25 –169.95o (c 0.2, CHCl3), with the molecular formula C20H23NO5, as determined by HRESIMS (observed m/z 358.1653 [M + H]+) and NMR
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