Redetermination of 14-deoxy­andrographolide

The title compound [systematic name: ent-3β-hydr­oxy-8(17),13(14)-labdadiene-16,15-olide], C₂₀H₃₀O₄, contains two trans fused six-membered rings, with a lactone ring at the end of an equatorial side chain. The six-membered rings are in chair conformations and the lactone ring is planar. There is an infinite chain of both inter- and intra­molecular O—H...O hydrogen bonds along the b axis. The present study is a confirmation of the results of previous structure determinations of 14-deoxyandrographolide by Medforth, Chang, Chen, Olmstead & Smith [J. Chem. Soc. Perkin Trans. 2 (1990), pp. 1011--1016] and Rajnikant, Gupta, Singh, Lal, Gupta & Varghese [Mol. Cryst. Liq. Cryst. Sect. C (1996), 6, 227–233].