TARAPACOL 15-ACETATE, A NEW DITERPENOID FROM GRINDELIA-TARAPACANA PHIL

In the title compound, 15-acetoxy-14(S)-hydroxy-13-epi-manoyl oxide {I UPAC systematic name: methyl-1H-naphtho[2,1-b]pyran-3-yl)-2-hydroxyeth yl acetate}, C22H38O4, rings A and B have chair conformations. Ring C adopts a boat conformation with the 16-methyl group in an axial positi on and the bulky glycol monoacetate group in an equatorial position. R ing systems A/B and B/C (conventional IUPAC labdane diterpenoid nomenc lature) are trans fused about the C(5)-C(10) and C(8)-C(9) bonds, resp ectively. The present study establishes the relative stereochemistry a t the C(14) position.