Having a methyl on the 1 position certainly increases euphoria:
Oxazepam<Temazepam
Lorazepam<Lormetazepam
Nitrazepam<Nimetazepam
Other substitutions at the 1 position seem to decrease activity in most cases
Halazepam<diazpeam
Then, replacing the amide with a triazolo ring makes things better.
Diazepam<Alprazolam
A methyl side-chain coming of the triazolam ring makes things better as well...
Estazolam<Alprazolam
Other side chains can increase potency more.
Alprazolam<Adinazolam
A '2 halo group makes the drug a lot stronger
Nimetazpem<flunitrazepam
Cllonazepam<Nitrazepam
Replacing the amide with a thioamide reduces T1/2
Quazepam<halazepam
Some unusual 1 position substitution
Cinolazepam
doxefazepam
Replacing the benzodiazipines benzene ring can reduce the T1/2 while maintaining potency.
Brotizolam
Etizolam
But some reduce potency
Bentazepam
The most potent replacement of the benzene ring seems to be pyrazolo analogs. They also have good water solubility. The toxicity may well be an issue, having said this.
Zolazepam
It's possible to make stimulant benzos.
GYKI-52895
Ones that replicate the effects of alcohol
QH-II-66
And ones that reverse the effects of alcohol and benzodiazipines
RO 15-4513
Or just the effects of benzodiazipines
Brentazinil
The area currently being studied the most is the subtitution of the 1 position but as some of these agents prove, the 7 position can make or break a benzo. Cl,Br,NO2 are agonist, N=N=N are antagonists and CCH (ethylene) produces agonists at certain sites. The '2 can be F,Cl,Br or =N- as agonists. Doesn't seem to confur antagonist properties.
One place that there has been little research is the substitution of the 3 position. -OH, -COO are sometimes used, these reduce the T1/2. Since many benzos are oxidised at the 3 position before being expelled, 'hardening' this site might well improve T1/2. Meclonazepam puts a methyl there, but the methyl can easily be oxidised. If a fluorine were placed there, then the drug should be hardened.
I would be interested to see if anyone has further experimented on the C ring. It has been replaced with a pyridine ring (bromazepam) which retains potency, but reduction to a cyclohexene ring reduces potency (tetrazepam) greatly. A 2 thienyl group would seem to be a logical step although this would surely decrease the T1/2