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Master's Dissertation
DOI
https://doi.org/10.11606/D.46.2019.tde-25112019-160532
Document
Author
Full name
Charles Roberto de Almeida Silva
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2019
Supervisor
Committee
Marzorati, Liliana (President)
Botelho, Marcos Felipe Pinatto
Giarolla, Jeanine
Title in Portuguese
Preparação de β-hidróxi-α-amino ésteres e aziridinas
Keywords in Portuguese
β-hidróxi-α-aminoácidos
Aziridina
Catálise de transferência de fase
Diastereosseletividade
Oxazolidina
Abstract in Portuguese
Os β-hidróxi-α-aminoácidos são intermediários sintéticos importantes, em especial para a preparação de compostos biologicamente ativos. À procura de um método simples para prepará-los, foi investigada a adição aldólica de aldeídos aromáticos a uma cetimina da glicina, seguida de hidrólise das oxazolidinas assim obtidas. Estas reações foram efetuadas em condições de transferência de fase, e utilizando como base NaOH(aq), na concentração de 1% (m/v). Dois diferentes tipos de catalisadores, o Aliquta-336 e o brometo de N-cetil-trimetilamônio foram testados, conduzindo a resultados semelhantes. Nas reações em que foram empregados o p-nitro ou m-clorobenzaldeído, não foi observada diasterosseletividade. Porém, a mesma reação efetuada com p-clorobenzaldeído conduziu quase que exclusivamente à oxazolidina correspondente de estereoquímica cis. Na tentativa de obter oxazolidinas opticamente ativas, foram empregados catalisadores de transferência de fase de configuração definida. No entanto, tais catalisadores não foram efetivos, obtendo-se oxazolidinas com muito baixo excesso enantiomérico. Alternativamente, as reações de adição aldólica foram realizadas em etanol, na presença de carbonato de sódio. Nestes casos, as oxazolidinas obtidas apresentavam estereoquímica trans. Na etapa de hidrólise das oxazolidinas, os rendimentos foram bons e os β-hidróxi-α-aminoácidos assim preparados foram transformados nas correspondentes aziridinas tosiladas, pela reação direta com cloreto de tosila em sistema sólido/líquido, empregando carbonato de potássio como base.
Title in English
Preparation of β-hidroxy-α-amino esters and aziridines
Keywords in English
β-hidroxy-α-aminoácids
Aziridine
Diastereoselectivity
Oxazolidine
Phase-transfer catalysis
Abstract in English
Os β-hidróxi-α-aminoácids are useful synthetic precursors to several biologically active compounds. In a search for a practical method for obtaining this kind of compounds, the aldol addition of aromatic aldehydes to a ketimine of glycine was investigated under phase-transfer conditions. The concentration of the aqueous alkali was 1% (w/v), and the performance of two catalysts, Aliquat-336 and N-cetyltrimethylammonium bromide, was evaluated, leading to similar results. Poor diastereoselectivity was observed for aldol additions to p-nitro or m-chlorobenzaldehyde. However, for the same reaction, employing p-chlorobenzaldehyde, the anti-aldol was formed almost exclusively, leading to the corresponding cis-oxazolidine, by in situ intramolecular cyclization. Aiming the preparation of optically active oxazolidines, the aldol addition was performed in the presence of chiral phase-transfer catalysts that proved to be inefficient for this kind of reaction, leading to products with very low enantiomeric excess. Alternatively, the trans-oxazolidines were prepared in a liquid/solid system, using ethanol as solvent and solid potassium carbonate as base. The hydrolysis of the prepared oxazolidines afforded the expected β-hydroxy-α-aminoácids in good yields, and such compounds were readily transformed into the corresponding N-tosyl-aziridines, by one-pot tosylation of the amino and hydroxyl groups, followed by ring closure.
 
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Publishing Date
2019-12-06
 
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