Are you a member of Blacklight.in samadhi? I've posted a lot of (what I hope is) really good information about the structural activity relationships of depressants.
Most relevant to your particular desires has to be the GABA-A a1-selective ligands. These seem to require a pentagonal ring w/ one or more nitrogens (three seems to be the max, but I'm not sure) and usually one or more double bonds, but thalidomide has none, but I can't find data on it's selectivity. Off of that a chain that looks like this: C-C(=O)-N, with the N usually being disubstituted (except of course, again in thalidomide and CL-218-872).
This basic structure should make the potential psychedelic-sedatives obvious: it's obviously something that the basic tryptamine structure can be modified to accomodate, simply changing the amine to an amide (ie: a ketone on the alpha carbon).
I can't find anything on the 5HT2a selectivity or the sort of potency we could expect from these.
Obviously the hope would be for much stronger preference for 5HT2a over GABA-A a1-subunit containing receptors since a1 agonists are so well known as strong hypnotics and amnesics.
I think that these might make great potential psychedelics for the anxiety-impaired. I'm certainly one of these, so I've been quite restricted from using psychedelics except when I've had a long period of preperation before partaking in any of the sacraments.
With PTSD and potentially unsettling, upsetting and unwanted flashbacks so common after a particularly bad trip (they are of course extremely uncommon on the whole with psychedelic users, but the risk goes greatly up among those unfortunate enough to have had a really bad trip), these offer two advantages: they'd be less prone to inducing bad trips, and if one were to develop, as they certainly can (look at the bad 'trips' resulting from Zolpidem), taking a higher dose could be used to produce complete amnesia of the experience.
A lot of the more new-agish psychedelic users will be quick to say "that won't solve anything, that'll simply push it into the back of the mind and repress the experience." However, when considering the horrible things that have happened to and done by people under the influence of GABAergic drugs that produced complete amnesia, and don't seem to harm or even affect the experiencee unless discovered through some other route, I think it's safe to say that it's simply hippy hogwash to borrow a phrase I once heard at a George Bush 2004 rally.
(to think, as I originally wrote all that, it was only one sentence, and now it's only two! I could never parody Kurt Vonnegut, that's for sure)