1,2,5-Oxadiazolo[3,4-b]glycyrrhetinic acid

The title compound [systematic name: 11-oxo-2,3-(oxy­dinitrilo)olean-12-en-29-oic acid], C(30)H(42)N(2)O(4), contains a linear array of five six-membered rings and a five-membered heterocyclic ring. The C ring, containing an α,β-unsaturated ketone, has a slightly distorted half-chair conformation, as does the A ring, with N—C—C angles 125.3 (5), 111.2 (4), 124.9 (5) and 109.2 (5)°, while the other three six-membered rings adopt chair conformations. The enanti­omer has been assigned by reference to unchanging chiral centres in the synthetic procedure. An intramolecular C—H⋯O interaction is present. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link the mol­ecules.