Acetic acid (3S,8R,9S,10R,13S,14S,15S,16S)-3-(tert-butyl-diphenyl-silanyloxy)-17-eth-(E)-ylidene-15-hydroxy-10,13-dimethyl-2,3,4,7,8,9,10,11,12,13,14,15,16,17-tetradecahydro-1H-cyclopenta[a]phenanthren-16-yl ester