3-((2R,3S)-5-Hydroxy-2,3,8,8-tetramethyl-4-oxo-3,4-dihydro-2H,8H-benzo[1,2-b:5,4-b']dipyran-10-yl)-butyric acid methyl ester AIDS-171581 AIDS171581 Isocordato-oblongic acid methylester