Calicheamicin was noted in the previous post as a natural product with antitumour properties and having many weird structural features such as  an unusual “enedidyne” motif. The representation is shown below. A partial structure shown below for Calicheamicin replaces the -(CH ₂ )4- substructure with a four carbon chain that includes two sp ² centres instead of two sp ³ centres.