L-xylo-Heptonic acid,3,6-anhydro-2,5,7- trideoxy-5-[[(3S,3aS,8bR)-3-(3-furanyl)-4,5- dihydro-1-oxo-1H,3H-3a,8b-methanobenzo[1,- 2-b:3,4-c’]difuran-7-yl]methyl]-4,6-di-Cmethyl-,ç-lactone