Regiospecific phosphohydrolases from Dictyostelium as tools for the chemoenzymatic synthesis of the enantiomers d-myo-inositol 1,2,4-trisphosphate and d-myo-inositol 2,3,6-trisphosphate: non-physiological, potential analogues of biologically active d-myo-inositol 1,3,4-trisphosphate