How many dipeptides are possible by the reaction of glycine and alanine?

Glycine has no chiral centre. Alanine has one chiral centre. The products are alanylglycine and glycinylalanine (I not sure whether this is the correct name or not. Please excuse), and I got a total of 4 isomers for each, (using D,L notation and optical isomers) so I got a total of $4+4=8$ products.

But the answer is given as $9$.

Where is my mistake?


1 Answer 1


The number of isomers are ${9}$ as shown below.

  • AlaAla has ${4}$ isomers.
  • AlaGly has ${2}$ isomers.
  • GlyAla has ${2}$ isomers.
  • GlyGly has ${1}$ isomer.

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