There has recently been discussion in the "
entheogenic effects of NMT" thread of how 5-O substituted tryptamines are prone to oxidative cyclisation at the 4-position of the indole ring. This seems pertinent here as melatonin is a 5-oxygenated tryptamine. It could go that way via a Pictet-Spengler incorporating the acetyl group to form an azepino[5,4,3-cd]indole, or oxidatively at the sidechain nitrogen to form a pyrido[4,3,2-cd]indole, although to me the latter seems a bit less likely and requires basic conditions.
If the purported psychoactivity of O-methyl nordehydrobufotenine is anything to go by, the analogue corresponding to melatonin may show some kind of activity. But surely somebody must have looked into that by now?
I'm just imagining an acetyl group instead of that methyl group on the pyrido nitrogen:

“There is a way of manipulating matter and energy so as to produce what modern scientists call 'a field of force'. The field acts on the observer and puts him in a privileged position vis-à-vis the universe. From this position he has access to the realities which are ordinarily hidden from us by time and space, matter and energy. This is what we call the Great Work."
― Jacques Bergier, quoting Fulcanelli