Development of a high affinity and stereoselective photoaffinity label for the D-1 dopamine receptor: synthesis and resolution of 7-[125I]iodo-8-hydroxy-3-methyl-1-(4'-azidophenyl)-2,3,4,5-tetrahydro- 1H-3-benzazepine.
In an earlier paper, we reported the development of (+-)-7-iodo-8-hydroxy-3-methyl-1-(4'-azidophenyl)-2,3,4,5-tetrahydro- 1H-3-benzazepine (I-MAB) and its 125I analogue ([125I]I-MAB) as selective, high affinity photoaffinity labels for the D-1 dopamine receptor. In this report, we now describe the complete synthesis and resolution of I-MAB and the pharmacological characterization of the stereoisomers in canine striatal membranes. R-(+)-I-MAB showed highly specific dopamine D-1 receptor binding (KD = 0.28 nM) and binds selectively and stereoselectively to the D-1 receptor. These results further confirm the previous suggestion that, in the benzazepine series of DA agonists and antagonists, the activity principally resides in the R-(+) enantiomer, the S-(-) enantiomer being considerably less potent or inactive. Moreover, R-(+)-[125I]I-MAB, upon photolysis, identifies the ligand-binding subunits of the neuronal D-1 receptor, with an apparent Mr of 74,000, 62,000, and 51,000 as assessed by autoradiography following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Photoincorporation of R-(+)-[125I]I-MAB into these polypeptides was stereoselectively blocked by D-1 dopaminergic ligands with an appropriate pharmacologic profile for the receptor. R-(+)-[125I]I-MAB should thus prove to be a useful stereoselective photoaffinity label for the further characterization of the D-1 receptors.
Research Biochemicals Inc., Natick, Massachusetts 01760.
J L
JL
Neumeyer
N
N
Baindur
J
J
Yuan
G
G
Booth
P
P
Seeman
H B
HB
Niznik
D000345:Affinity Labels / Q000138:chemical synthesis / Q000378:metabolism; D000818:Animals; D001386:Azides / Q000138:chemical synthesis / Q000378:metabolism*; D001552:Benzazepines / Q000138:chemical synthesis / Q000378:metabolism*; D001569:Benzodiazepines / Q000138:chemical synthesis* / Q000378:metabolism; D001667:Binding, Competitive; D055598:Chemical Phenomena; D002621:Chemistry; D003342:Corpus Striatum / Q000378:metabolism; D004285:Dogs; D015195:Drug Design; D066298:In Vitro Techniques; D008970:Molecular Weight; D010777:Photochemistry; D011954:Receptors, Dopamine / Q000378:metabolism*; D013329:Structure-Activity Relationship
D000345:Affinity Labels; D001386:Azides; D001552:Benzazepines; D011954:Receptors, Dopamine; C058320:7-iodo-8-hydroxy-3-methyl-1-(4-azidophenyl)-2,3,4,5-tetrahydro-1H-3-benzazepine; D001569:Benzodiazepines