10.2 Synthesis of α-Amino Acids

LEARNING GOALS

After   Chapter 10.2,   you will    be  able    to:

Recall  the required    reactants   and product types   for the Strecker    and Gabriel synthesis

reactions

Identify    the reaction    types   found   in  the Strecker    and Gabriel synthesis   reactions

Synthesis of amino acids occurs by an astonishing variety of mechanisms in vivo. In the lab, several
simple reaction mechanisms are exploited to make amino acids neatly and efficiently.

STRECKER SYNTHESIS

In the Strecker synthesis, one starts with an aldehyde, ammonium chloride (NH 4 Cl), and potassium
cyanide (KCN), as shown in Figure 10.6. The carbonyl oxygen is protonated, increasing the
electrophilicity of the carbonyl carbon. Then, as seen in Chapter 6 of MCAT Organic Chemistry
Review, ammonia can attack the carbonyl carbon, forming an imine. The imine carbon is also
susceptible to nucleophilic addition reactions; thus, the CN– anion from KCN attacks, forming a
nitrile group (–C≡N). The final molecule at the end of Step 1 is an aminonitrile—a compound
containing an amino group (–NH 2 ) and a nitrile group.