On
the basis of the activity of 1,2,4-benzothiadiazine 1,1-dioxides
as positive allosteric modulators of AMPA receptors, thiochroman 1,1-dioxides
were designed applying the isosteric replacement concept. The new
compounds expressed strong modulatory activity on AMPA receptors in vitro, although lower than their corresponding benzothiadiazine
analogues. The pharmacokinetic profile of three thiochroman 1,1-dioxides
(12a, 12b, 12e) was examined in vivo after oral administration, showing that these compounds
freely cross the blood–brain barrier. Structural analysis was
achieved using X-ray crystallography after cocrystallization of the
racemic compound 12b in complex with the ligand-binding
domain of GluA2 (L504Y/N775S). Interestingly, both enantiomers of 12b were found to interact with the GluA2 dimer interface,
almost identically to its benzothiadiazine analogue, BPAM344 (4). The interactions of the two enantiomers in the cocrystal
were further analyzed (mapping Hirshfeld surfaces and 2D fingerprint)
and compared to those of 4. Taken together, these data
explain the lower affinity on AMPA receptors of thiochroman 1,1-dioxides
compared to their corresponding 1,2,4-benzothiadiazine 1,1-dioxides.