l-1,2,3,4-Tetrahydro-8-methoxy-5-(methylthio)-2-naphthalenamine: a potent and selective agonist at alpha 1-adrenoceptors.

1,2,3,4-Tetrahydro-8-methoxy-5-(methylthio)-2-naphthalenamine (SK&F-89748) has been resolved into d and l enantiomers and characterized pharmacologically. The more active isomer is the l, which has the S configuration as established by single-crystal X-ray diffraction studies. This compound is a potent and selective alpha 1-agonist with an EC50 in the isolated perfused rabbit ear artery of 9 +/- 2 nM. In several preparations, it has shown an alpha 1/alpha 2 selectivity ratio of over 100 and will be a useful tool for characterizing receptor subtypes.