Estudo químico e biológico de Microlicia parviflora (Melastomataceae): sazonalidade dos óleos essenciais, metabolômica comparativa e isolamento de metabólitos

Abstract

Microlicia parviflora (Melastomataceae) is a poorly studied species, but plants of the genus have been reported to exhibit promising biological activities. Therefore, in the present study, the chemical composition and biological potential were evaluated through three distinct approaches. Initially, the essential oils from leaves collected throughout one year were investigated for their antimicrobial potential, and their chemical compositions were determined by mass spectrometry. The oils exhibited promising antibacterial activity against different oral pathogens, with the most notable inhibitory results obtained against Porphyromonas gingivalis and Actinomyces naeslundii, with minimum inhibitory concentration (MIC) values of 0.39 µg mL–1. Through multivariate statistical analyses, it was possible to group the oils obtained at different times of the year, relating their chemical composition to the rainy and dry seasons; the chemical profile and biological potential of the essential oils from the flowers were also evaluated, which showed a slightly different composition from that of the leaves and were active against the same bacteria. In a second approach, extracts were obtained by maceration of the leaves, flowers, and branches using hexane and ethanol. These extracts were tested against the same bacteria, Candida species, and the protozoa Trypanosoma cruzi and Leishmania infantum. The hexane extracts were active against six of the bacteria tested, with MIC values ranging from 12.5 to 100 µg mL–1, and against L. infantum, with an effective concentration (EC50) ranging from 0.9 to 3.8 µg mL–1. The ethanolic extracts from the three organs and the more polar partitions of the leaves and branches were active against Candida species, including the multidrug-resistant species C. auris, with MIC values of 2.93 µg mL–1. Finally, a comparative study of the chemical composition of leaves, flowers, branches, and roots was performed using metabolomic techniques. With the aid of mass spectrometry and statistical analyses, it was possible to differentiate the organs, showing that the chemical composition of the branches and roots is similar, whereas that of the leaves and flowers is more distinct. These results were also observed by nuclear magnetic resonance spectroscopy. The methanolic extracts of the four organs were tested against phytopathogens associated with different cultivars and against human colorectal and prostate cancer cells. The extracts were active in both assays, showing 100% inhibition of the pathogen Phytophthora infestans and against both types of cancer cells tested. In addition, the study led to the isolation of two compounds obtained from different organs: quercitrin obtained from the ethyl acetate partition of the leaves and tricoumaroyl-spermidine obtained from the ethyl acetate partition of the flowers. Both were reported for the first time in the species, and the spermidine derivative was reported for the first time in the genus. This was the first study conducted on other organs of the species, as well as the first study to investigate the biological activities tested.