title: 4,5-Dihydroxy-2,3-pentanedione
text: # 4,5-Dihydroxy-2,3-pentanedione
  
  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 $CH_3C(O)C(O)CH(OH)CH_2OH,$ 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. The (S)-stereoisomer occurs naturally. It is typically hydrated, i.e., one keto group has added water to give the geminal diol.
  
  DPD is produced by degradation of S-adenosylhomocysteine by the action of the enzyme S-ribosylhomocysteinase. The compound probably does not exist as depicted above, but as an equilibrium mixture of three hydrates.
  
  DPD is a precursor to borate diester, which is known as autoinducer-2 (AI-2). AI-2 is a signaling molecules found in quorum sensing. It is produced and recognized by many Gram-negative and Gram-positive bacteria. AI-2 is synthesized by the reaction of DPD with boric acid and is recognized by the two-component sensor kinase LuxPQ in Vibrionaceae.
  
  