Structure of cyclic dihydroxyacetone phosphate dimethyl acetal, a cyclic DHAP precursor, in the crystalline state.

The six-membered cyclic phosphate diester, 5,5-dimethoxy-2-oxo-1,3,2-dioxaphosphorinane-2-ol, the dimethyl acetal of cyclic dihydroxyacetone phosphate, (MeO)(2)cDHAP, was obtained by the isolation of an intermediate in the basic hydrolysis of the cyclic triester derivative. The compound had been isolated in the form of the crystalline cyclohexylammonium (cha) salts: (cha)[(MeO)(2)cDHAP].3H(2)O (5a) and (cha)[(MeO)(2)cDHAP].H(2)O (5b), which were then converted into the free acid: (H(5)O(2))[(MeO)(2)cDHAP] (5c) and then into a series of different salts: Na[(MeO)(2)cDHAP].2H(2)O (5d), K[(MeO)(2)cDHAP].1.5H(2)O (5e), K[(MeO)(2)cDHAP].0.5H(2)O (5e'), Ca[(MeO)(2)cDHAP](2).2H(2)O (5f), CaK[(MeO)(2)cDHAP](3).2H(2)O (5g) and NH(4)[(MeO)(2)cDHAP] (5h). The synthesis of the compounds, their crystallization and crystal structures determined by X-ray crystallography are described. The most interesting structural feature observed in 5a-g anions in the crystalline state is the chair conformation of the P/O/C/C/C/O 1,3,2-dioxaphosphorinane ring, which is generally not flattened, in contrast to the deformations often observed in the analogous aryl derivatives (also in (MeO)(2)cDHAP(Ph); Slepokura, K.; Lis, T. Acta Crystallogr. Sect. C2004, 60, o315-o317). However, the anion in crystal 5h is disordered and exists in two conformations, 76% of which is the skew, S, conformation, not observed so far in the compounds of related structure.