Dihydroxyacetone phosphate, DHAP, in the crystalline state: monomeric and dimeric forms

It was shown that dihydroxyacetone phosphate may exist in both monomeric DHAP (C3H7O6P) and dimeric DHAP-dimer (C6H14O12P2) form. Monomeric DHAP was obtained in the form of four crystalline salts: CaCl(DHAP)·2.9H2O (7a), Ca2Cl3(DHAP)·5H2O (7b), CaCl(DHAP)·2H2O (7c), and CaBr(DHAP)·5H2O (7d) by crystallization from aqueous solutions containing DHAP acid and CaCl2 or CaBr2, or by direct crystallization from a solution containing DHAP precursor and CaCl2. At least one of the salts is stable and may be stored in the crystalline state at room temperature for several months. The dimeric form was obtained by slow saturation of free DHAP syrup with ammonia at −18 °C and isolated in the form of its hydrated diammonium salt (NH4)2(DHAP-dimer)·4H2O (8). The synthesis of the compounds, their crystallization, and crystal structures determined by X-ray crystallography are described. In all 7a–d monomeric DHAP exists in the monoanionic form in an extended (in-plane) cisoid conformation, with both hydroxyl and ester oxygen atoms being synperiplanar to the carbonyl O atom. The crucial structural feature is the coordination manner, in which the terminal phosphate oxygen atoms act as chelating as well as bridging atoms for the calcium cations. Additionally, the DHAP monoanions chelate another Ca2+ by the α-hydroxycarbonyl moiety, in a manner observed previously in dihydroxyacetone (DHA) calcium chloride complexes. In dimeric 8 the anion is a trans isomer with the dioxane ring in a chair conformation with the hydroxyl groups in axial positions and the phosphomethyl group in an equatorial position.

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