Calcipotriol EP Impurity I

(1aR,1’R,2S,3a’R,4R,6aS,7a’R)-1′-((2R,5S,E)-5-cyclopropyl-5-hydroxypent-3-en-2-yl)-7a’-methyl-1′,2,2′,3,3′,3a’,4,5,5′,6,6a,6′,7′,7a’-tetradecahydro-1aH-spiro[cyclopropa[a]indene-1,4′-indene]-2,4-diol