A diketopiperazine derivative of quinapril

The title compound, ethyl 2-(1,2,3,4,5,6,11,11a-octahydro-3- methyl-1\,4-dioxopyrazino[1\,2-b]isoquinolin-2-yl)-4-phenylbutanoate, is formed due to cyclization of quinapril in solution. The configurations at the three chiral centres are all S. The six-membered B and C rings assume half-chair and boat confirmations, respectively. The molecules in the lattice are stabilized by van der Waals contacts.

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