Synthesis and Structure−Activity Relationships of a Novel Series of 2,3,5,6,7,9-Hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-Dioxide KATP Channel Openers: Discovery of (−)-(9S)-9-(3-Bromo-4-fluorophenyl)-2,3,5,6,7,9- hexahydrothieno[3,2-b]quinolin-8(4H)-one 1,1-Dioxide (A-278637), a Potent KATP Open