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Authors
Abstract(s)
A humanidade sempre utilizou plantas medicinais como fonte primária no
tratamento de algumas doenças. Em África, as plantas do género Psydrax são popularmente
usadas na medicina tradicional para o tratamento de várias doenças e sintomas, incluindo
malária, febre, dores de cabeça, edema, reumatismo, diarreia, conjuntivites, micoses e
outras doenças inoficiosas. Existem estudos sobre os compostos presentes em algumas das
plantas do género mencionado e responsáveis pela sua bioatividade, mas pouco se sabe
sobre o perfil químico de Psydrax locuples (K. Schum.) Bridson. Assim, com o objetivo de
contribuir para a descoberta de novos constituintes e avaliação de propriedades bioativas
dessa espécie, foram realizados estudos com as folhas, muito utilizadas na medicina
tradicional no sul de Moçambique.
Os extratos foram preparados por maceração das folhas secas e moídas,
sequencialmente, com solventes de polaridade progressiva. Os compostos solúveis em
acetato de etilo, na maioria dos casos após acetilação, foram purificados por cromatografia
em coluna e preparativa em camada fina. A elucidação estrutural destes compostos foi feita
através da espetroscopia de RMN e espetrometria de massa (HRMS).
Foram isolados derivados acetilados de dois triterpenos (ácido ursólico e 11β-
hidroxiursólico) que, posteriormente, foram esterificados com trimetilsilildiazometano de
forma a converter o grupo carboxílico em éster metílico. Quer o composto 11β-
hidroxiursólico, quer os seus derivados eram desconhecidos. Também foram identificados
nove dissacáridos acetilados dos quais cinco são cianogénicos. Previamente, já haviam sido
descobertos numa planta de outra espécie, dois dissacáridos cianogénicos relacionados com
os isolados.
O potencial antioxidante dos extratos/frações foi determinado pela atividade
captadora de radicais 2,2-difenil-picril-hidrazilo (DPPH), poder redutor (PR) e inibição da
descoloração do β-caroteno. Todos os extratos/frações, apresentaram resultados
satisfatórios, principalmente os extratos de metanol e água (EC50DPPH = 0,29 e 0,32
mg/mL, respetivamente; EC50PR = 0,31 e 0,30 mg/mL, respetivamente; EC50β-caroteno =
0,52 e 0,31 mg/mL, respetivamente). O potencial antitumoral foi avaliado in vitro, em quatro linhas celulares tumorais
humanos (HeLa, HepG2, MCF7 e NCI-H460), pelo método da sulforodamina B. Todos os
extratos e compostos isolados (sobretudo triperpenos e dissacáridos) revelaram atividade
inibitória do crescimento celular. O extrato de acetato de etilo acetilado foi o que
apresentou maior atividade em todas as linhas celulares testadas (80 μg/mL<GI50<219
μg/mL). A ausência de toxicidade dos extratos foi confirmada e ensaiada em culturas
primárias de células de fígado de porco (PLP2). Os resultados dos ensaios de bioatividade
vêm realçar o potencial medicinal das folhas de P. locuples tão utilizadas na medicina
tradicional em Moçambique.
Since ancient times, mankind has used medicinal plants as primary source to treat some diseases. In Africa, plants belonging to the genus of Psydrax are popularly used in the traditional medicine to treat several symptoms and diseases, such as fevers, malaria, edema, headache, rheumatic pains, diarrhea, conjunctivitis, mycoses and other infectious diseases. There are available studies on the compounds present in some of the plants of the mentioned genus and responsible for their bioactivity, but the chemical profile of Psydrax locuples (K. Schum.) Bridson is still unknown. Therefore, in order to contribute to the discovery of new compounds and evaluation of bioactive properties of this species, studies with its leaves, highly used in the traditional medicine in south of Mozambique, were carried out. The extracts were obtained by sequential maceration of the powder of the dried leaves of P. locuples using different solvents and increasing polarity. The soluble compounds in ethyl acetate, most of the cases after their acetylation, were purified by column and thin-layer preparative chromatographies. Their structural elucidation was done by NMR spectroscopy and mass spectrometry (HRMS). We have isolated acetylated derivative of two triterpenes (ursolic and 11β- hydroxyursolic acids) that were subsequently esterified with trimetysilyldiazomethane to convert the carboxylic to an ester group. 11β-Hydroxyursolic acid and its derivatives were unknown compounds. Furthermore, nine diglycoside compounds, which five are cyanogenic compounds, were also identified. Two cyanogenic diglycosides related with the ones isolated in the present work were previously identified in other species. Bioassays were conducted in order to know the biological potential of extracts and isolated compounds. The antioxidant activity of all the extracts/fractions was evaluated through DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity, reducing power (RP) and β-carotene bleaching inhibition. All the extracts/fractions showed satisfactory results, especially the methanolic and water extracts (EC50DPPH = 0.29 and 0.32 mg/mL, respectively; EC50RP = 0.31 and 0.30 mg/mL, respectively; EC50β-carotene = 0.52 and 0.31 mg/mL, respectively). The in vitro antitumor potential of all the extracts and isolated compounds was evaluated in four human tumor cell lines (HeLa, HepG2, MCF7 and NCI-H460) by Sulforhodamine B assay. All the extracts and isolated compounds (especially triterpenes and diglycosides) showed results against tumor cell lines. The acetylated ethyl acetate extract expressed better inhibition of the cell growth in all the lines tested (80 μg/mL<GI50<219 μg/mL). The absence of toxicity of the extracts was confirmed in a primary culture of porcine liver cells (PLP2). The results obtained in the bioassays validate the medicinal potential of P. locuples leaves, commonly used in the traditional medicine of Mozambique.
Since ancient times, mankind has used medicinal plants as primary source to treat some diseases. In Africa, plants belonging to the genus of Psydrax are popularly used in the traditional medicine to treat several symptoms and diseases, such as fevers, malaria, edema, headache, rheumatic pains, diarrhea, conjunctivitis, mycoses and other infectious diseases. There are available studies on the compounds present in some of the plants of the mentioned genus and responsible for their bioactivity, but the chemical profile of Psydrax locuples (K. Schum.) Bridson is still unknown. Therefore, in order to contribute to the discovery of new compounds and evaluation of bioactive properties of this species, studies with its leaves, highly used in the traditional medicine in south of Mozambique, were carried out. The extracts were obtained by sequential maceration of the powder of the dried leaves of P. locuples using different solvents and increasing polarity. The soluble compounds in ethyl acetate, most of the cases after their acetylation, were purified by column and thin-layer preparative chromatographies. Their structural elucidation was done by NMR spectroscopy and mass spectrometry (HRMS). We have isolated acetylated derivative of two triterpenes (ursolic and 11β- hydroxyursolic acids) that were subsequently esterified with trimetysilyldiazomethane to convert the carboxylic to an ester group. 11β-Hydroxyursolic acid and its derivatives were unknown compounds. Furthermore, nine diglycoside compounds, which five are cyanogenic compounds, were also identified. Two cyanogenic diglycosides related with the ones isolated in the present work were previously identified in other species. Bioassays were conducted in order to know the biological potential of extracts and isolated compounds. The antioxidant activity of all the extracts/fractions was evaluated through DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity, reducing power (RP) and β-carotene bleaching inhibition. All the extracts/fractions showed satisfactory results, especially the methanolic and water extracts (EC50DPPH = 0.29 and 0.32 mg/mL, respectively; EC50RP = 0.31 and 0.30 mg/mL, respectively; EC50β-carotene = 0.52 and 0.31 mg/mL, respectively). The in vitro antitumor potential of all the extracts and isolated compounds was evaluated in four human tumor cell lines (HeLa, HepG2, MCF7 and NCI-H460) by Sulforhodamine B assay. All the extracts and isolated compounds (especially triterpenes and diglycosides) showed results against tumor cell lines. The acetylated ethyl acetate extract expressed better inhibition of the cell growth in all the lines tested (80 μg/mL<GI50<219 μg/mL). The absence of toxicity of the extracts was confirmed in a primary culture of porcine liver cells (PLP2). The results obtained in the bioassays validate the medicinal potential of P. locuples leaves, commonly used in the traditional medicine of Mozambique.
Description
Mestrado em cooperação com a Universidade de Salamanca