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Synthesis and kinetic investigation of the selective acydolysis of para-substit...
Lima, Sílvia M. M. A. Pereira; Pinto, Filipa C. S. C.; Ventura, Cristina; Albuquerque, Lídia; Maia, Raquel M. Gonçalves; Maia, Hernâni L. S.Several derivatives of N-phenylacetyl-N-benzyl-alpha,alpha-dimethylglycine cyclohexylamide and their alpha,alpha-dibenzylglycine analogues were synthesised by a Ugi-Passerini reaction. In addition, a few analogues of the former but having an N-phenyl instead of a benzyl group at the nitrogen atom were synthesised. The compounds in each of these three sets differed from each other at the position 4 of the N-benz...
Kinetic investigation of the effect of the amino acid side chains in the select...
Wei-Qun, Jiang; Lima, Sílvia M. M. A. Pereira; Ventura, Cristina; Costa, Susana P. G.; Albuquerque, Lídia; Maia, Raquel M. GonçalvesAccurate kinetic measurements of the rate constants for the acidolysis of five N-acetyl-N-(4-methoxybenzyl)-alfa,alfa-trialkyl glycine cyclohexyl amides in TFA were performed at 25.00 ºC and the reactions monitored by HPLC. The results were in all cases consistent with a first order behaviour with respect to the substrate. No direct correlation was obtained with this data between rate constant values and struct...
Dialkyl imidazolinones from alpha,alpha-dialkyl glycines
Costa, Susana P. G.; Maia, Hernâni L. S.; Lima, Sílvia M. M. A. PereiraIn recent years, our group has been involved in the use of the Ugi-Passerini reaction for the synthesis of several alpha,alpha-dialkylglycines. The C-terminal amide bond of the resulting Ugi adducts 1 proved to be very sensitive to TFA, cleaving readily by a mechanism involving an oxazolinium-type intermediate 2. This intermediate allows in situ functionalization of the C-terminus by reaction with several nucle...
An improved approach for the synthesis of alfa,alfa-dialkyl glycine derivatives...
Lima, Sílvia M. M. A. Pereira; Costa, Susana P. G.; Maia, Hernâni L. S.A general and simple strategy for routine peptide synthesis with alfa,alfa-dialkyl glycines taking advantage of the four-component Ugi-Passerini reaction is presented. The isonitrile required for the reaction can be relatively simple and its selection based on cost, as the group it generates is easily removed under acidic conditions; in addition, this removal is not visibly affected by the bulkiness of the alfa...
An improved approach to the synthesis of N-acyl-alpha,alpha-dialkyl glycines an...
Lima, Sílvia M. M. A. Pereira; Costa, Susana P. G.; Maia, Hernâni L. S.Owing to steric hindrance, syntheses of and reactions with alfa,alfa-dialkylglycines are very slow; thus, most methods of peptide synthesis are of little use to handle these compounds when the alfa-alkyl groups are larger than methyl. Ugi’s four-component reaction is appropriate to synthesise these amino acids [1], but for peptide synthesis it presents two drawbacks, i.e. (i) peptide isonitriles racemise above ...
C-terminal amide bond stability of peptides containing C,alfa,alfa-disubstitute...
Lima, Sílvia M. M. A. Pereira; Costa, Susana P. G.; Maia, Hernâni L. S.We have since long been interested in the synthesis of C,alfa,alfa-disubstituted glycines using the Ugi Four Component Condensation Reaction. Recently we have improved this method of synthesis by using 4-methoxybenzyl amine as the amine component of the Ugi reaction (A), which allowed an important simplification in the subsequent cleavage of the product. During the removal of the 4-methoxybenzyl group with hot ...
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