As actinobactérias são uma reconhecida fonte de metabólitos secundários bioativos com grande diversidade estrutural e funcional. Dentre elas, o gênero Streptomyces é sem dúvida o mais explorado, correspondendo a cerca de 75% dos metabólitos secundários estudados, e por dois terços dos antibióticos conhecidos. Dessa forma, ainda é crescente a necessidade de novos herbicidas com perfil de baixa toxicidade ambiental e novos mecanismos de ação, para a substituição de produtos que são utilizados extensivamente há anos. Grandes avanços tecnológicos têm sido alcançados em termos de instrumentação analítica nas últimas décadas, tornando a espectrometria de massas a técnica mais eficiente e robusta na identificação de metabólitos secundários, principalmente quando acoplada a técnicas cromatográficas de ultra eficiência (UHPLC-MS). Nessa dissertação foi explorada a diversidade metabólica de actinobactérias isoladas do bioma Caatinga para a identificação de metabólitos secundários com atividade fitotóxica. Foram produzidos 166 extratos brutos de actinobactérias, das quais, 27 apresentaram algum nível de atividade fitotóxica contra Lemna minor. Devido pronunciada bioatividade (MIC = 6,25 ?g) o extrato bruto da actinobactéria, CAAT 7-52, foi selecionado para desreplicação, caracterização e fracionamento guiado por bioensaios, e, ao mesmo tempo, um estudo taxonômico foi realizado para determinar o posicionamento filogenético do novo isolado. A análise da sequência do gene 16S rRNA suportou a classificação da linhagem no gênero Streptomyces e mostrou que CAAT 7-52 formou uma linha filética distinta junto com a linhagem tipo de Streptomyces actinomycinicus, com um valor de identidade da sequência de 99,0%. No extrato bruto de CAAT 7-52 foi identificada a Albociclina como responsável pela atividade fitotóxica (MIC = 3,12 ?g), assim como alguns compostos análogos. O monitoramento da massa micelial seca e produção de Albociclina mostrou uma maior produção do composto ativo aos 21 dias de crescimento. Esse extrato foi submetido a ensaios de inibição de germinação, onde apresentou atividade contra sementes de buva (Conyza canadensis) (MIC = 12,5 ?g), alface (Lactuca sativa) e rúcula (Eruca sativa). Variações no meio de cultivo mostraram uma produção seletiva de Albociclina nos meios de cultivo PMB e Czapeck-GL. Ensaios de fitotoxicidade contra Lemna minor, utilizando o fermentado do meio PMB sem extração com solventes orgânicos, mostrou atividade em uma diluição de 20%. Portanto, foi possível demostrar através desse estudo o grande potencial das actinobactérias na produção de metabólitos secundários bioativos e da espectrometria de massas como técnica analítica na identificação dos compostos ativos. / Actinobacterias are a well know source of bioactive secondary metabolites with great structural and functional diversity. Among them, the Streptomyces genus is certainly the most explored, corresponding to about 75% of studied secondary metabolites, and for two thirds of known antibiotics. Thus, there is still a growing need for new herbicides with low environmental toxicity e new modes of action, for the replacement of products that have been broadly used for years. Great technological progress has been achieved in analytical instrumentation in the last few decades, making mass spectrometry the most efficient and robust technique to identify secondary metabolites, mainly when accoupled to ultra-performance chromatographic techniques (UHPLC-MS). In this essay, was explored the metabolic diversity of the actinobacterias isolated from the Caatinga biome to identification of secondary metabolites with phytotoxic activity. Were produced 166 crude extracts from actinobacterias, from this, 27 showed some phytotoxic activity against Lemna minor. Due to noticeable bioactivity (MIC = 6,25 ?g) the crude extract from actinobacteria CAAT 7-52, was selected to dereplication, characterization and bioassay guided fractionation, and, at the same time, a taxonomic study was carried out to determinate the phylogenetic location of the new isolated. The analysis of 16S rRNA gene sequence supported the lineage classification on the genus Streptomyces and established that CAAT 7-52 assembled a distinct phyletic line together with the lineage type of Streptomyces actinomycinicus, with an identity sequence value of 99,0%. In the crude extract CAAT 7-52, Albocycline was identified as the responsible for the phytotoxic activity (MIC = 3,12 ?g), so as some analogous compounds. The mycelial dry mass and Albocycline production monitoring revealed a major production of the active compound at 21 days of growth. This extract was subjected to germination inhibition assays, where revealed activity against horseweed (Conyza canadensis) (MIC = 12,5 ?g), lettuce (Lactuca sativa) and arugula (Eruca sativa) seeds. Variations in the culture media showed a selective production of Albocycline in the PMB and Czapeck-GL culture media. Phytotoxicity assays against Lemna minor, applying the fermented PMB media without organic solvents extractions, revealed activity with a 20% dilution. Therefore, through this study was able to demonstrate the great potential of the actinobacterias in the production of bioactive secondary metabolites and the mass spectrometry as analytical technique to identification of the active compounds.

There is a profound need for new antibiotics which overcome bacterial resistance. The predominant source for these is natural products; however, they are often quickly rendered ineffective due to antibiotic resistance. A proven method in drug discovery is improving the properties of natural products through diverted total synthesis (DTS). Of particular interest is promysalin, which is produced by Pseudomonas putida, and selectively inhibits the growth of Gram-negative pathogenic bacteria Pseudomonas aeruginosa at nanomolar concentrations. The work herein describes modifications to the side chain which were shown to modulate antibacterial potency and specificity. A similarly inspired approach to countering antibiotic resistance is the targeted modification of a single carbon to silicon, motivated by the proven success of this substitution shown in pharmaceuticals and amino acids. The target for this modification is albocycline, a known macrolactone antibiotic that exhibits potent antibiotic activity against S. aureus. Replacing the C4 carbon of albocycline with silicon will provide sila-albocycline with enhanced hydrogen bonding properties and altered lipophilicity due to the slight changes from the carbon to silicon atom. In addition, there is anticipated intrinsic stability of the silanol toward rearrangement reactions than carbon-based. The proposed synthesis diverts from the known total synthesis of albocycline, as reported by the Andrade Group. This work details the efforts made towards the total synthesis of sila-albocycline. Lastly, there is untapped potential for UV-promoted photochemistry to create molecular scaffolds, which may lead to novel synthetic routes to complex molecules in addition to providing new polycycles that may expand current medicinal products. The work herein describes the synthesis of tethered chloro- and methoxy-substituted benzyl alcohols to 2-pyridones and the resulting products when exposing the solution to ultraviolet light. This generated new polycycles with complex structures which have unexplored biological or medicinal properties. / Chemistry