Vitamin D2 Impurity 20

(S, Z) -3- (2- ((1R,3aS,7aR, Z) -1- ((2S,5R, E) -5,6-dimethylhept-3-en-2-yl) -7a-methyloctahydro-4H-inden-4-ylidene) ethylidene) -4-methylenecyclohexyl 3,5-dinitrobenzoate