Amino cidos y P ptidos Amino cidos alfa -amino cido: glicina - PowerPoint PPT Presentation

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Amino cidos y P ptidos Amino cidos alfa -amino cido: glicina

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Amino cidos y P ptidos Amino cidos alfa -amino cido: glicina beta-amino cido gama-amino cido: GABA Estructura general de un -amino cido: Los amino cidos son ... – PowerPoint PPT presentation

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Title: Amino cidos y P ptidos Amino cidos alfa -amino cido: glicina


1
Aminoácidos y Péptidos
2
Aminoácidos
Los aminoácidos son compuestos bifuncionales,
contienen un grupo amino básico y un grupo
carboxilo ácido. Se nombran según la posición
relativa de dichos grupos
Estructura general de un ?-aminoácido
Tienen valor como bloques biológicos porque
pueden formar péptidos entre el NH2 de un
aminoácido y el COOH de otro mediante enlaces
amida
3
La Glycina es el aminoácido más simple y el único
que es aquiral. Para el resto, el carbono ? es
un centro de quiralidad.
4
Síntesis de aminoácidos
5
  • Uno de los métodos más viejos data del siglo
    diecinueve y es simplemente una sustitución
    nucleofílica en la cual el amoníaco reacciona con
    un ácido alfa halocarboxílico.

6
Síntesis de Strecker
7
Síntesis del ester malónico modificada
Sigue una hidrólisis
8
Péptidos
9
El enlace peptídico
Enlace peptídico
10
  • Por conveción, los péptidos se escriben tal que
    el grupo amino está a la izquierda y el grupo
    carboxilo a la derecha.

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12
Análisis de aminoácidos
13
  • The chemistry behind amine acid analysis is
    nothing more than acid-catalyzed hydrolysis of
    amide (peptide) bonds. The peptide is hydrolyzed
    by heating in 6 M hydrochloric acid for about 24
    h to give a solution that contains all the amine
    acids. This mixture is then separated by,
    ion-exchange chromatography which separates the
    amine acids mainly according to their acid-base
    properties.

14
Hidrólisis parcial de aminoácidos
  • Trypsin, a digestive enzyme present in the
    intestine, catalyzes only the hydrolysis of
    peptide bonds involving the carboxyl group of a
    lysine or arginine residue.
  • Chymotrypsin, another digestive enzyme, is
    selective for peptide bonds involving the
    carbexyl group of amine acids with aromatic side
    chains (phenylalanine, tryrosine, tryptophan).
  • Carboxypeptidases, catalyzes only the hydrolysis
    of the peptide bond to the C-terminal amine acid.
    In addition to these, many other digestive
    enzymes are known and their selectivity exploited
    in the selective hydrolysis of peptides.

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16
Análisis del grupo terminal
  • As we saw in the preceding section,
    carboxypeptidase-catalyzed hydrolysis cleaves the
    C-terminal amino acid and so can be used to
    identify it. What about the N terminus?

17
  • The N-terminal amino group is free and can act as
    a nucleophile. Sanger's method for N-terminal
    residue analysis involves treating a peptide with
    1-fluoro-2,4-dinitrobenzene, which is very
    reactive toward nucleophilic aromatic
    substitution.

18
Reactivo de Sanger
19
  • The amino group of the N-terminal amino acid
    displaces fluoride from 1-fluoro-2,4-
    dinitrobenzene and gives a peptide in which the
    N-terminal nitrogen is labeled with a
    2,4-dinitrophenyl (DNP) group.

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21
La degradación de Edman
  • A peptide reacts with phenyl isothiocyanate to
    give a phenylthiocarbamoyl (PTC) derivative
  • This PTC derivative is then treated with an acid
    in an anhydrous medium to cleave the amide bond
    between the N-terminal amino acid and the
    remainder of the peptide.
  • When the PTC derivative is treated with acid in
    an anhydrous medium, the sulfur atom of the CS
    unit acts as an internal nucleophile, and the
    only amide bond cleaved under these conditions is
    the one to the N-terminal amino acid.
  • The product of this cleavage, called a
    thiazolone, is unstable under the conditions of
    its formation and rearranges to a
    phenylthiohydantoin (PTH), which is isolated and
    identified by comparing it with standard samples
    of PTH derivatives of known amino acids.

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Síntesis de péptidos
24
Protección del grupo amino
25
  • Z se puede remover fácilmente mediante
    hidrogenólisis en presencia de paladio

26
  • A related N-terminal-protecting group is
    tert-butoxycarbonyl, abbreviated Boc

27
  • Like the benzyloxycarbonyl protecting group, the
    Boc group may be removed by treat- ment with
    hydrogen bromide (it is stable to hydrogenolysis,
    however)

28
Protección del grupo carboxilo
  • Carboxyl groups of amino acids and peptides are
    normally protected as esters. Methyl and ethyl
    esters are prepared by Fischer esterification.
    Deprotection of methyl and ethyl esters is
    accomplished by hydrolysis in base. Benzyl esters
    are a popular choice because they can also be
    removed by hydrogenolysis. Thus a synthetic
    peptide, protected at both its N terminus with a
    Z group and at its C terminus as a benzyl ester,
    can be completely deprotected in a single
    operation.

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Formación del enlace peptídico
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