Acidic and anionic forms of 1,3‐cyclic dihydroxyacetone phosphate (cDHAP) dimethyl acetal

The six‐membered cyclic phosphate diester, 5,5‐dimethoxy‐2‐hydroxy‐1,3,2‐dioxaphosphorinan‐2‐one, C₅H₁₁O₆P or (MeO)₂cDHAP, which is the dimethyl acetal of cyclic dihydroxyacetone phosphate (cDHAP), has been obtained in the form of two new cyclohexylammonium (cha) salts, cyclohexylammonium 5,5‐dimethoxy‐2‐oxo‐1,3,2‐dioxaphosphorinan‐2‐olate monohydrate, (cha)(MeO)₂cDHAP]·H₂O or C₆H₁₄N⁺·C₅H₁₀O₆P⁻·H₂O, and cyclohexylammonium 5,5‐dimethoxy‐2‐oxo‐1,3,2‐dioxaphosphorinan‐2‐olate, (cha)(MeO)₂cDHAP] or C₆H₁₄N⁺·C₅H₁₀O₆P⁻, as well as in the form of the anhydrous free acid, (MeO)₂cDHAP. It is shown that protonation of the cyclic phosphate group influences the chair conformation of the P/O/C/C/C/O 1,3,2‐dioxaphosphorinane ring, and that differences in the ring conformation correlate with different deformations observed in the ionized and protonated phosphate groups. The ring is more evenly puckered in the anions, in contrast with the flattening observed in the structure of the free acid.