MOLECULAR NETWORKS: AN ANALYSIS ON ANNOTATIONS AND DISCOVERY OF NEW ASSETS. To speed up the discovery of bioactive natural products (NP), chemists have sought advanced approaches in analytical and computational chemistry in attempt to organize and extract information from large data sets. In this sense, the molecular networks (MN) successfully organized enormous sets of mass spectrometry (MS) data together with samples metadata information in an intuitive visualization in the spectral similarity networks format. GNPS (Global Natural Products Social Molecular Networking), a free online platform for storing and processing MSn data, is a leading application of spectral matching with public databases aimed at the dereplication and discovery of new bioactive products through molecular networks. In this review, we address the concept of GNPS spectral similarity networks, as well as their complementary computational tools, benefits and limitations applied in NP studies associated with dereplication, chemical ecology, functional genetics and determination of biosynthetic pathways.

Metabolomics has played a central role in various areas of plant sciences, offering new perspectives for the advancement of agriculture, drug discovery, chemical ecology and taxonomy. Plant metabolomics (identification and quantification) aims to understand the relationship between biological systems and genetic, pathological and or environmental stimuli in terms of differential expression of the metabolism. Owing to the unique challenges, such studies require multidisciplinary skills involving biology, chemistry, statistics, and computer science for the extraction and complete understanding of information. In this sense, this review summarizes the main procedures that involve the steps of plant metabolomic study (design of experiments, sample preparation, analytical methods and data analysis), providing a comprehensive overview, showing the main challenges and limitations and possible solutions for the different approaches used.

Um método racional e seletivo de cromatografia de alta eficiência acoplado à espectrometria de massas (CLAE-EM) com ionização por electrospray e analisador do tipo quadrupolo em tempo-de-voo em sequência (ESI-QToF-MS/MS) foi desenvolvido para a desreplicação de derivados fenólicos presentes em Qualea grandiflora e Qualea cordata. Os extratos para a análise foram selecionados por meio dos resultados de atividade antioxidante revelados no ensaio in vitro com DPPH. A análise por HPLC-ESI-QToF-MS/MS foi realizada por detecção contínua das relações massa/carga em alta resolução e pela técnica MS/MS de colisão induzida para fragmentação dos íons moleculares selecionados. A desreplicação da fração AcOEt do extrato hidroalcoólico dos caules de Q. grandiflora permitiu a detecção dos flavonoides: 3',4',5',5,6,7-hexahidroxi-8-metilflavanona, 8-metil-naringenina e 3',7-dimetoxi-8-metil-4',5,7-trihidroxiflavanona, assim como os derivativos da benzofenona (bis(4,6-dimetoxi-2-hidroxi-3-metilfenil)-metanona, 3',4'-dimetoxi-8-metil-5,6,7-trihidroxiflavanona, 7-metoxi-6-metil-3',4',5-trihidroxiflavanona, 6,8-dimetil-3'-metoxi-4',5,7-trihidroxiflavanona e 3',5'-dimetoxi-6,8-dimetil-4',5,7-trihidroxiflavanona) foram detectados na fração AcOEt do extrato hidroalcoólico das folhas de Q. cordata.

A rational and selective method using on-line high-performance liquid chromatography (HPLC) coupled with electrospray quadrupole time-of-flight tandem mass spectrometry (ESI-QToF-MS/MS) was established for the dereplication of phenolic derivatives from Qualea grandiflora and Qualea cordata. The selection of the extracts was based on the antioxidant capacity measured by in vitro DPPH assay. The HPLC-ESI-QToF-MS/MS analysis was conducted by on-flow detection, using high-resolution mass/ratio ions as well as collision induced MS/MS experiments for selected protonated ions. The dereplication of the EtOAc fraction from the hydro-alcohol extract from the stem bark of Q. grandiflora allowed the detection of the flavonoids: 3',4',5',5,6,7-hexahydroxy-8-methylflavanone, 8-methyl-naringenine and 3',7-dimethoxy-8-methyl-4',5,7-trihydroxyflavanone, as well as a benzophenone derivatives: bis(4,6-dimethoxy-2-hydroxy-3-methylphenyl)-metanone, 3',4'-dimethoxy-8-methyl-5,6,7-trihydroxyflavanone, 7-methoxy-6-methyl-3',4',5-trihydroxyflavanone, 6,8-dimethyl-3'-methoxy-4',5,7-trihydroxyflavanone and 3',5'-dimethoxy-6,8-dimethyl-4',5,7-trihydroxyflavanone were detected in the EtOAc fraction from the hydro-alcohol extract from the leaves of Q. cordata.