Crystal and molecular structure of L-cis-3,6-dimethyl-2,5-piperazinedione (L-alanyl-L-alanyl-2,5-diketopiperazine)

The crystal structure of L -cis-3, 6-dimethyl-2,5-piperazinedione (L -alanyl-L -alanyl-2,5-diketopinerazine) has been determined. The unit cell is triclinic with a = 8.05, b = 6.08, c = 5.15 Å, α = 131.7°, β = 82.4°, γ = 106.6°. The space group is P1 with one molecule per unit cell. The six-membered ring is found to be nonplanar with an angle between the two amide group planes of 26°. One amide group deviates slightly from planarity. The experimental molecular model is discussed in terms of its flexibility.