(1R,4R,5R,6R,6aR,9R,9aS)-4,5,6a,7,8,9-Hexahydro-1,5,6a-trihydroxy-5,9-dimethylspiro[6H-4,9a-methanocyclopenta[d]oxocin-6,3-oxetane]-2,2(1H)-dione