Griseusin B

(1R)-4'α-Acetoxy-3,3',4,4',5,5',6',10-octahydro-3'α,9-dihydroxy-6'β-methyl-5,10-dioxospiro[1H-naphtho[2,3-c]pyran-1,2'-[2H]pyran]-3α-acetic acid