4,5-Dihydroxy-2,3-pentanedione (DPD) is an organic compound that occurs naturally but exists as several related structures.

The idealized formula for this species is CH3C(O)C(O)CH(OH)CH2OH, but it is known to exist as several other forms resulting from cyclization.

It is not stable at room temperature as a pure material, which has further complicated its analysis.

It is typically hydrated, i.e., one keto group has added water to give the geminal diol.

[3][4] AI-2 is synthesized by the reaction of DPD with boric acid[5] and is recognized by the two-component sensor kinase LuxPQ in Vibrionaceae.