Biosynthesis Flashcards
What is nature’s enol equivalent?
What is its reactivity like?
Nature uses acetyl co-enzyme A as its enol. The ketone in the actyl group can tautomerise to an enol.
Acetyl CoA has the same reactivity as a thioester in the lab - the equilibrium is 50:50 between the keto and enol form.
What reaction can acetyl CoA alone undergo in nature?
Draw the mechanism.
Acetyl CoA undergoes Claisen reactions in nature, where the keto and enol forms react to make acetoacetyl CoA.
How does nature run reductive amination?
In nature, two cofactors and an aminotransferase enzyme are used for reductive amination.
The two cofactors are called pyridoxamine and pyridoxal.
What are two common reactions that the two cofactors are used for?
- reversible synthesis of amino acids from keto acids via amination/deamination
- decarboxylation of amino acids to give amines
Draw the mechanism for the reversible synthesis of amino acids from keto acids.
How does nature’s methylation occur?
Draw the mechanism(s).
Nature’s methylation uses s-adensoyl methionine (SAM).
What are the three classes of natural products?
- Alkaloids
- Polyketides
- Terpenes
Where do alkaloids come from?
Most alkaloids come from an amino acid biosynthetic precursor. The most common amino acids used are ornithine, lysine, tryptophan, phenylalanine and tyrosine.
What are the important reactions in the biosynthesis of alkaloids?
- Decarboxylation
- Deamination of amino acids then decarboxylation
- Imine/iminium ion formation
- Mannich reaction
- Methylation
Draw curly arrows to demonstrate what the Mannich reaction is.
What are pyrrolidine alkaloids synthesised from?
Give an example of a pyrrolidine alkaloid.
Pyrrolidine alkaloids include a 5-membered N-containing ring. Most of these are from ornithine as a biosynthetic precursor. An example is hygrine.
Draw the mechanism for hygrine synthesis.
Draw the mechanism for the synthesis of tropinone from hygrine.
Where do piperidine alkaloids come from?
Give an example and draw its structure.
Most 6-membered rings in piperidine alkaloids come from lysine. One example is pseudopelletierine.
Draw the mechanism for the biosynthesis of pseudopelletierine
*here, only one amine is methylated. This shows how nature can be both regio- and stereoselective.