A number of new pyrrolobenzothiazepine derivatives and a pyrrolobenzothiazocine derivative have been synthesized and evaluated for their affinity towards the 'peripheral- type'benzodiazepine receptor (PBR). The new compounds were tested in rat cortex, a tissue expressing a high density of mitochondrial PBR. Some of the pyrrolobenzothiazepines exhibited IC50 values in the low nanomolar range as measured by the displacement of [ ...