CYCLIC-DI-AMP SODIUM SALT CRYSTAL

A lyophilized product of cyclic-di-AMP requires special production equipment and is thus not suitable for large-scale production. Crystals of cyclic-di-AMP free acid are unstable under severe conditions at 105°C. Then, the present invention addresses the problem of providing a cyclic-di-AMP crystal that can be easily acquired in a large amount and is very stable under the severe conditions at 105°C. Crystals of c-di-AMP sodium salt according to the present invention are extremely stable even under the severe conditions at 105°C. Further, the crystals of c-di-AMP sodium salt according to the present invention can be prepared in a large amount by a simple process including adjusting a c-di-AMP aqueous solution at pH 5.2-12.0 and then adding an organic solvent thereto.