Phosphoric acid, mono((4-amino-6a,7,8,9a-tetrahydro-7-hydroxyfuro(2',3':4,5)thiazolo(3,2-e)purin-8-yl)methyl) mono(3,4,6a,7,8,9a-hexahydro-8-(hydroxymethyl)-4-oxofuro(2',3':4,5)thiazolo(3,2-e)purin-7-yl) ester, (6aS-(6aalpha,7alpha,8beta,9aalpha))-(6'aS-(6'aalpha,7'alpha,8'beta,9'aalpha))-