The primary structure is composed of a circle comprised of 15 kinds of molecules, while the 4th and 5th sites of carbon are intergrated with a circle of unsaturated oxygen, and a lipid chian is ligated at the 13th site of carbon.

• 其骨架由一个15元环组成，在环的碳4和碳5位又与一个不饱和的4元氧环相联，在碳十三位还带一个酯基侧链。