Amino acids Fischer projections

D- and L- are older configurational descriptors used to denote the configuration of chiral molecules, especially carbohydrates and a-amino acids. Fischer projections are used to assign the symbols D- and L-. 

Fig. 2. Spatial view of an L-amino acid Fischer-projection of l- and D-amino acids...

We mentioned in Section 7 6 that the d l system of stereochemical notation while outdated for most purposes is still widely used for carbohydrates and amino acids Likewise Fischer projections find their major application m these same two families of compounds... 

Glycine is the simplest anino acid and the only one in Table 27.1 that is achiral. The a-carbon atom is a chirality center in all the others. Configurations in amino acids are normally specified by the d, l notational system. All the chiral amino acids obtained from proteins have the l configuration at their- a-carbon atom, meaning that the amine group is at the left when a Fischer projection is arianged so the carboxyl group is at the top. 

L-Amino acid (Section 27.2) A description of the stereochemistry at the a-carbon atom of a chiral amino acid. The Fischer projection of an a-amino acid has the amino group on the left when the carbon chain is vertical with the carboxyl group at the top. 

Except for cysteine, only S amino acids occur in proteins. Several R amino acids are also found in nature, however. (ft)-Serine is found in earthworms, and (R)-alanine is found in insect larvae. Draw Fischer projections of (fl)-serine and (J )-alanine. Are these Don amino acids ... 

In the simplest and oldest system the formula of the compound is compared with a standard substance taken as the key compound. In the series of a amino or a -hydroxy acid, the key is the top part of the projection formulas (Fischer projection formulas). 

Figure 1 Stereochemical drawing and Fischer projection of an L-a-amino acid, where R is the side chain of the amino acid.

Fischer polypeptide synthesis org chem A synthesis of peptides in which a-amino acids or those peptides with a free amino group react with acid halides of a-haloacids, followed by amination with ammonia. fish-ar pal-e pep,tTd. sin tha sas ) Fischer projection orgchem) A method for representing the spatial arrangement of groups around chiral carbon atoms the four bonds to the chiral carbon are represented by a cross, with the assumption that the horizontal bonds project toward the viewer and the vertical bonds away from the viewer fish-ar pra.jek-shon) Fischer s salt See cobalt potassium nitrite. fish-3rz solt)... 

Fischer further proposed that the amino acid in this orientation could be projected onto the paper and drawn with ordinary lines for all the bonds. This gives the previously shown Fischer projection formula of... 

Stereochemistry of Amino Acids Naturally occurring amino acids belong to the T-family. That is, when the amino acid is drawn as a Fischer projection, with the carboxyl group at the top and the side chain at the bottom, the amino group is on the left, as shown in Figure 12.45. 

Figure 1.4 The D/L configurations of amino acids. Note that the carboxylic acid group must be drawn at the top and the R group at the bottom of the Fischer projection. Stereogenetic centres in the R group do not affect the D/L assignment...

Use perspective drawings and Fischer projections to show the stereochemistry of D- and L-amino acids. Explain why the naturally occurring amino acids are called L-amino acids. Problems 24-37 and 53... 

A Fischer projection of the a-carbon of an L-amino acid is pictured above. For most L-amino acids For cysteine ... 

In a-amino acids, the L-compounds are those in which the NH2 group is on the left-hand side of the Fischer projection in which the COOH group appears at the top. 

Amino acids. These retain the d,l- system because all of the protein amino acids belong to the L- series, but not all of them are S- according to the sequence rnle. See Chapter 5. Biochemists often use the d,l- system for synthetic compounds derived from amino acids where most organic chemists would use R.S-. In a-amino acids, the L-componnds are those in which the NH2 gronp is on the left-hand side of the Fischer projection in which the COOH group is at the top. Conversely, the o-compounds are those in which the NH2 group is on the right-hand side. 

The amino acid threonine, (2S ,3/ )-2 amino-3-hydroxybutanoic acid, has two chuai-ity centers. Draw a Fischer projection of threonine. ... 

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