2-Butenoic acid, 2-methyl-, 4b,7,7a,8-tetrahydro-1,2,3-trimethoxy-5-oxo-5H-benzo[3.4]furo[3',4':5,6]cyclohepta[1,2-f][1,3]benzodioxol-8-yl ester, (4b.alpha.,7a.beta.,8.beta.)- NSC172956 STEGANANGIN