Natural products occupy a central role as the majority of currently used antibiotic and anticancer agents. Among these are type-II polyketide synthase (PKS)-derived molecules, or polyketides, which are produced by many representatives of the genus Streptomyces. Some type-II polyketides, such as the tetracyclines and the anthracycline doxorubicin, are currently employed as therapeutics. However, several polyketide molecules exhibit promising biological activity, but due to toxic side effects or solubility concerns, remain undeveloped as drugs. Gilvocarcin V (GV) (topoisomerase II inhibitor) has a novel mechanism of action: [2+2] cycloaddition to thymine residues by the 8-vinyl side chain and cross-linking of histone H. Mithramycin blocks transcription of proto-oncogenes c-myc and c-src by forming an Mg2+-coordinated homodimer in the GC-rich minor groove of DNA. The purpose of this research was to investigate the biosynthesis of several type II polyketide compounds (e.g. chrysomycin, elloramycin, and mithramycin) with the goal of improving the bioactivities of these drugs through combinatorial biosynthesis. Alteration of the glycosylation pattern of these molecules is one promising way to improve or alter the bioactivities of these molecules. To this end, an understanding of the glycosyltransferases and post-polyketide tailoring enzymatic steps involved in these biosynthetic pathways must be established. Four specific aims were established to meet these goals. In specific aim 1, the biosynthetic locus of chrysomycin A was successfully cloned and elucidated, which afforded novel biosynthetic tools. Chrysomycin monooxygenases were found to catalyze identical roles to their gilvocarcin counterparts. Cloning of deoxysugar constructs (plasmids) which could direct biosynthesis of ketosugars, NDP-D-virenose, and NDP-D-fucofuranose in foreign pathways was undertaken in specific aim 2. Finally, these “sugar” plasmids were introduced into producer organisms of elloramycin and mithramycin pathways in specific aims 3 and 4 to interrogate the endogenous glycosyltransferases in order to alter their glycosylation patterns. These experiments resulted in the successful generation of a newly glycosylated tetracenomycin, as well as premithramycin, and mithramycin analogues. In specific aim 4, a new mithramycin analogue with an altered sugar pattern rationally designed and improved structural features was generated and structurally elucidated.

Antraciclinas estão entre os mais eficazes quimioterápicos contra o cancer. São fármacos glycosídicos compostos pelo carboidrato daunosamina ligado a uma aglicona hidróxi antraquinona, e atuam por intercalação ao DNA, geração de estresse oxidative e envenenamento de topoisomerase II. Apesar de sua utilidade terapêutica, multirresistência e cardiotoxicidade grave são importantes limitações decorrentes do tratamento com antraciclinas, estimulando a descoberta de novos análogos, por exemplo através de glicodiversificação. Este trabalho objetivou explorar azido glicosídeos, a serem combinados com agliconas de antraciclinas para gerar novos glicosídeos. Em uma estratégia semi-sintética, daunorrubicinona e doxorrubicinona protegida foram glicosiladas com doadores 2-azido glucosídicos e -galactosídicos, além de glicais. Uma varredura de metodologias de glicosilação envolveu cloretos, imidatos e tioglicosídeos, sendo os promotores com melhores rendimentos HgO/HgBr2 (4-52%) e TMSOTf (38-41%); para glucais e galactais, catalisadores de Au(I) and Cu(I) forneceram moderados rendimentos (15-46%), mas o sistema mais eficiente foi o organocatalisador de tiouréia e ácido fosfórico (18-95%). A clivagem dos grupos de proteção foi desafiadora, dificultando e atrasando a obtenção dos glicosídeos livres. Mediante desproteção, os glicosídeos obtidos incluíram glucosídeo 49 (13%), 2-azido glucosídeo 51 (34%), 2-desóxi glucosídeo 58 (11%) e 2-desóxi galactosídeo 61 (85%), todos com o esqueleto de daunorrubicina. Em ensaios de proliferação celular, os glicosídeos 61? e 61? foram testados em linhagens de células tumorais humanas HeLa, MDA-MB-231 e MCF-7 e um modelo de células sadias (HDF), com IC50 na faixa de 27.1 a 74.6 ?M para o anômero ?, e superior a 250 ?M para o anômero ?. Estudos preliminares com cardiomiócitos humanos derivados de células-tronco induzidas foram inconclusivos para estabelecer um modelo experimental de toxicidade cardíaca. / Anthracyclines are ranked among the most effective chemotherapeutics against cancer. They are glycoside drugs comprised by the aminosugar daunosamine linked to a hydroxyanthraquinone aglycone, and act by DNA-intercalation, oxidative stress generation and topoisomerase II poisoning. Regardless of their therapeutic value, multidrug resistance and severe cardiotoxicity are important limitations arising from anthracycline treatment, prompting the discovery of novel analogues, for instance through glycodiversification. This work aimed to exploit azido glycosides, to be combined with anthracycline aglycone and generate novel glycosides. In a semi-synthesis approach, both daunorubicinone and protected doxorubicinone were glycosylated with conveniently functionalised 2-azido glucosyl and galactosyl donors, as well as glycals. A screening of glycosylation protocols involved glycosyl chlorides, imidates and thioglycosides with the most successful promoters being HgO/HgBr2 (4-52% yield) and TMSOTf (38-41%); for glucals and galactals, Au(I) and Cu(I) catalysts gave moderate yields (15-46%), but thiourea-phosphoric acid was the most efficient catalyst system (18-95%). Cleavage of protecting groups proved challenging, hampering and delaying the obtention of free glycosides. Upon deprotection, the glycosides obtained included glucoside 49 (13%), 2-azido glucoside 51 (34%), 2-deoxyglucoside 58 (11%), and 2-deoxygalactoside 61 (85%), all with the daunorubicin scaffold. In cell proliferation assays, glycosides 61? and 61? were tested against human cancer cell lines HeLa, MDA-MB-231 and MCF-7 and a model of healthy cells (HDF), with IC50 in the range of 27.1 to 74.6 ?M for the ? anomer, and higher than 250 ?M for the ? anomer. Preliminary studies with human cardiomyocytes derived from induced pluripotent stem cells were inconclusive to establish a cardiac toxicity experimental model.