67055-57-6 Pentalenolactone G Spiro(oxirane-2,1'(2'H)-pentaleno(1,6a-c)pyran)-5'-carboxylic acid, 4',4'a,6'a,7',8',9'-hexahydro-8',8'-dimethyl-2',7'-dioxo-, (1'R-(1'alpha,4'aalpha,6'abeta,9'aS*))-