(8aS)-4a,4b-bis((E)-2-bromovinyl)-1,8-bis((2R,4S,5R)-4-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)tetrahydrocyclobuta[1,2-d:4,3-d’]dipyrimidine-2,4,5,7(3H,4aH,4bH,6H)-tetraone