Design. In structure− activity relationship (SAR) studies of 2, the (E)-acryloyl moiety was found to be indispensable for potent diuretic activity (unpublished results). Compounds in which the (E)-acryloyl moiety was replaced by (Z)-acryloyl, propionyl, or propioloyl were essentially inactive. Therefore, it was quite clear that the conformation of the acryloyl part of 2 was very important. The X-ray crystal structure of 2 (Figure 2) clearly indicated that the (E ...