(S)-(+)-Boldine (1) was brominated, chlorinated, and iodinated using molecu
lar bromine in acetic acid or N-halosuccinimides in trifluoroacetic acid. I
nitial halogenation occurs at C-3, followed (in the cases of chlorine and b
romine) by the less reactive C-8, to afford 3-haloboldines- and 3,8-dihalob
oldines (2-5). Using a 2:1 ratio of N-iodosuccinimide to boldine, however,
only the 3-iodo derivative 6 was obtained. Radioligand binding studies of t
hese products showed that halogenation of boldine at C-3 favors affinity fo
r D-1-(vs D-2-) dopaminergic receptors, attaining a low nanomolar IC50 valu
e in the case of 3-iodoboldine (6).