Main content
MCAT
Course: MCAT > Unit 9
Lesson 10: Proteins- Proteins questions
- Amino acid structure
- Alpha amino acid synthesis
- Classification of amino acids
- Peptide bonds: Formation and cleavage
- Four levels of protein structure
- Conformational stability: Protein folding and denaturation
- Non-enzymatic protein function
© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice
Alpha amino acid synthesis
Created by Tracy Kim Kovach.
Want to join the conversation?
- why is there a nh3+ in the final amino acid rather than nh2 as it should be?(4 votes)
- At biological PH (7) the amino acid ends are both charged. NH3+ on one end and COO- on the other.(19 votes)
- After the hydrolyzed step, why does the heat only remove one acid group (as opposed to both)?(9 votes)
- you need the second carbonyl group to act as an electron sink. See the part about b-keto acids in the below link: http://www.masterorganicchemistry.com/2012/08/14/the-malonic-ester-synthesis/(2 votes)
- at, she adds an acid to hydrolyze alpha-amino nitrile into alpha-amino acid; how did the Cyanide group turn into an carboxylic acid group? 5:00(4 votes)
- It is a pretty long mechanism. Basically what happens is the nitrogen in the cyanide keeps getting protonated by the acid until it wants to leave the carbon. While this is happening the carbon from the cyanide is gaining water from the acid group being deprotonated by the nitrogen until it is a carboxylic acid. Here is a link to a website that shows the steps with the mechanism.
http://science.uvu.edu/ochem/index.php/alphabetical/s-t/strecker-synthesis/(4 votes)
- personally im into gabriel synthesis more(4 votes)
- If you are synthesizing an amino acid with a more reactive R group - say glutamate or arginine - how do you prevent the R group from participating in either synthesis (Strecker or Gabriel)?(3 votes)
- There are protecting groups available for protecting essentially every R group found on an amino acid. Such amino acid derivatives are typically used in solid phase peptide synthesis when a long peptide is desired.(1 vote)
- Do both reactions produce a racemic mixture of amino acids?(2 votes)
- yes they both do since both synthesis start with a planar molecule!(3 votes)
- Do both reactions produce a racemic mixture of amino acids?(3 votes)
- yes, because both are starting with planar molecules, sorry for responding 6 years late hope you graduated as a doctor lol.(1 vote)
- is this is all what we have to know about Gabriel synthesis for the MCAT?(2 votes)
- Where is n-phthalimidomalonic ester found? Is it found in food?(2 votes)
- Is this a part of content category 1A?(1 vote)
Video transcript
Hey. So we're going to be talking
about amino acid synthesis. And we're just going to stick
with two of the main methods for synthesizing amino acids. And they both just
happened to be named after old German
chemists because synthesizing amino acids was probably
hot stuff back in the mid to late 1800s, And the
first method that we're going to be talking about
is Gabriel synthesis, named after Siegmund Gabriel. And the second method is
called Strecker synthesis, which is named after
Adolph Strecker. So let's start out with
Gabriel synthesis first. In Gabriel synthesis,
we begin with a molecule of what's called
phthalimidomalonic ester. So n-phthalimidomalonic ester
is what this molecule is called, and that's kind of a
mouthful so I'm just going to call this "thad." All righty, so
here's our molecule of what I'm going
to call "thad." And this is sort of the
foundation upon which we're going to build our
alpha amino acid. And so let me draw an
alpha amino acid over here to kind of remind us what
our end product or end goal is going to be. And so remember that an
amino acid has, first, the amino group, and
I'm going to draw it in the protonated form. And then we have
our alpha carbon, and then the R group, or
side chain, is over here. And then bound to
the alpha carbon is the hydrogen and a
carobxylic acid group. So if we come back over to
our molecule thad over here, we can see that
the nitrogen atom is going to serve
as our amino group. And then we have our alpha
carbon here in the center, and then our carboxylic
acid, here, is on the bottom. And then we have this temporary
ester group at the top. So I'm going to highlight
those key atoms for you here, the nitrogen and the alpha
carbon and the carbonyl carbon. And the reason
why we started out with all these other groups
attached to our key atoms is for various reasons. For example, our amide
is prevented or, quote, "protected" from
acting as a nucleophile by having this phthalimide
group attached to it. And then the carboxylic acid is
protected with this ethyl ester that's attached, and the
[INAUDIBLE] carbon is further activated by this additional
ester group at the top. Now in the presence
of a base and having a source of an alkyl
group, our molecule of thad will become alkylated
to look like this. So now you can see that
the alkyl group here has been substituted
onto the carbon atom, and so this is known
as the alkylated step. And then the next step
involves acid hydrolysis, which yields this molecule. And as you can see here,
the phthalimide group was hydrolyzed along
with the two esters. And this is the hydrolyzed step. And then finally, we
can add a little heat to decarboxylate this
molecule or remove its carboxyl group up top here. And we get our final
alpha amino acid. OK, so this is Gabriel
synthesis in a nut shell. So you start out with an
n-phthalimidomalonic ester, and then you add up a base and
a source of an alkyl group. And you get an alkylated
amide malonic acid here, and then you hydrolyze this to
get your carboxylic acid group as well as your amino group. Then you add a little
heat for decarboxylation, and you wind up with
the final amino acid that's produced here. And so now that we have
Gabriel synthesis down, let's move on to
Strecker synthesis here. So let's make a
little room for that. So next we have
Strecker's synthesis, and the Strecker
method is considered to be a somewhat more
elegant way of synthesizing amino acids because it's really
a lot more simple and efficient And just remember that
simplicity is elegant. And there are just three
starting components, and these are
ammonia, which serves as the precursor
for our amino group; potassium cyanide, which
serves as the precursor for the carboxylic
acid group; and then either an aldehyde
or a ketone, which serves as the scaffold on which
the amino and carboxylic acid groups will be bound. And this provides
the carbon that will become our alpha carbon. So let's take an
aldehyde and react it with ammonia in the
presence of an acid. This will give us an imine as
well as a molecule of water, and then the imine can
be protonated again in the presence of an acid. And this time, a
cyanide ion will attack the protonated
imine, which generates an alpha
amino nitrile. And then, finally,
the hydrolysis of this alpha amino nitrile
yields an alpha amino acid. And so there you have
it-- Strecker synthesis. You can see how it's a
very simple and efficient and, therefore, elegant way
of synthesizing amino acids.