G. Tarzia et al., 1-(2-ALKANAMIDOETHYL)-6-METHOXYINDOLE DERIVATIVES - A NEW CLASS OF POTENT INDOLE MELATONIN ANALOGS, Journal of medicinal chemistry, 40(13), 1997, pp. 2003-2010
A new series of indole melatonin analogues, bearing the amido ethyl si
de chain attached at the N-1 position of the indole nucleus, were synt
hesized and tested for their affinity for the melatonin receptor isola
ted from quail optic tecta in a series of in vitro ligand-binding expe
riments using 2-[I-125]iodomelatonin as the labeled ligand. The biolog
ical activity was evaluated using two models: effects on the forskolin
-stimulated cAMP accumulation in explants from quail optic tecta and e
valuation of the GTP gamma S index derived from competition experiment
s performed in the absence or presence of GTP gamma S. Compounds 2a an
d 2k-n, obtained by shifting the methoxy group and the ethylamido side
chain from the C-5 and C-3 positions of melatonin to the C-6 and N-1
positions of the indole nucleus, exhibited an affinity similar to that
of melatonin itself, as well as full agonist activity. Optimization o
f the C-2 substituent by introducing Br, phenyl, or COOCH3 (2b-d) resu
lted in a significantly enhanced affinity (in the picomolar range) and
improved agonist biological activity. Compounds lacking the methoxy g
roup and bearing an N-alicyclic group (2h-j) behaved as partial agonis
ts or antagonists.