Valnemulin impurity E – (3aS,4R,5S,6S,8R,9R,9aR,10R)-6-ethenyl-5-hydroxy-4,6,9,10-tetramethyl-1-oxodecahydro-3a,9-propano-3aH-cyclopenta[8]annulen-8-yl 2-hydroxyacetate (pleuromulin)