Indietro
Problema 1a
Draw three-dimensional representations of the following amino acids.
(a) L-phenylalanine
Problema 1b
Draw three-dimensional representations of the following amino acids.
(b) L-histidine
Problema 1c
Draw three-dimensional representations of the following amino acids.
(c) D-serine
Problema 1d
Draw three-dimensional representations of the following amino acids.
(d) L-tryptophan
Problema 2a
Most naturally occurring amino acids have chiral centers (the asymmetric α carbon atoms) that are named (S) by the Cahn–Ingold–Prelog convention (Section 5-3). The common naturally occurring form of cysteine has a chiral center that is named (R), however.
(a) What is the relationship between (R)-cysteine and (S)-alanine? Do they have the opposite three-dimensional configuration (as the names might suggest) or the same configuration?
Problema 2b
Most naturally occurring amino acids have chiral centers (the asymmetric α carbon atoms) that are named (S) by the Cahn–Ingold–Prelog convention (Section 5-3). The common naturally occurring form of cysteine has a chiral center that is named (R), however.
(b) (S)-Alanine is an L-amino acid (Figure 24-2). Is (R)-cysteine a d-amino acid or an L-amino acid?
Problema 3
The herbicide glyphosate (Roundup®) kills plants by inhibiting an enzyme needed for synthesis of phenylalanine. Deprived of phenylalanine, the plant cannot make the proteins it needs, and it gradually weakens and dies. Although a small amount of glyphosate is deadly to a plant, its human toxicity is quite low. Suggest why this powerful herbicide has little effect on humans.
Problema 4a
Draw the structure of the predominant form of
(a) isoleucine at pH 11.
Problema 4b
Draw the structure of the predominant form of
(b) proline at pH 2.
Problema 4d
Draw the structure of the predominant form of
(d) glutamic acid at pH 7.
Problema 4e(iii)
Draw the structure of the predominant form of
(e) a mixture of alanine, lysine, and aspartic acid at (iii) pH 2.
Problema 4e(i)
Draw the structure of the predominant form of
(e) a mixture of alanine, lysine, and aspartic acid at (i) pH 6;
Problema 6
Although tryptophan contains a heterocyclic amine, it is considered a neutral amino acid. Explain why the indole nitrogen of tryptophan is more weakly basic than one of the imidazole nitrogens of histidine.
Problema 7
Draw the electrophoretic separation of Ala, Lys, and Asp at pH 9.7.
Problema 8
Draw the electrophoretic separation of Trp, Cys, and His at pH 6.0.
Problema 9a
Show how the following amino acids might be formed in the laboratory by reductive amination of the appropriate α-ketoacid.
(a) alanine
Problema 10b
Show how you would use bromination followed by amination to synthesize the following amino acids.
(b) leucine
Problema 11a
Show how you would use a Strecker synthesis to make phenylalanine.
Problema 11b(1)
Propose a mechanism for each step in the synthesis in part (a).
Problema 11b(2)
Propose a mechanism for each step in the synthesis in part (a).
Problema 12b
Show how you would use a Strecker synthesis to make
(b) valine.
Problema 12c
Show how you would use a Strecker synthesis to make
(c) aspartic acid.
Problema 13
Suggest how you would separate the free L-amino acid from its acylated D enantiomer in Figure 24-5.
Problema 15
Give equations for the formation and hydrogenolysis of glutamine benzyl ester.
Problema 16
Give equations for the formation and hydrogenolysis of N-benzyloxycarbonyl methionine.
Problema 17
Use resonance forms to show delocalization of the negative charge in the Ruhemann's purple anion.
Problema 19a
Draw the structure of the phenylthiohydantoin derivatives of
(a) alanine.
Problema 19c
Draw the structure of the phenylthiohydantoin derivatives of
(c) lysine.
Problema 24a
Propose a mechanism for the coupling of acetic acid and aniline using DCC as a coupling agent.
Problema 27a
(a) The isoelectric point (pI) of phenylalanine is pH 5.5. Draw the structure of the major form of phenylalanine at pH values of 1, 5.5, and 11.
