we all know about o-desmethyltramadol and tapentadol but there are some really interesting tramadol analogs, some are around the strength of fentanyl. here are a few but I'm interested if anyone knows of others or of tapentadol analogs, if you do please post.
Faxeladol (racemic mix called Racefaxeladol) is Demethyldesoxy-tramadol, its around the potency of morphine. one of the isomers is stronger than the other but I don't know which. racefaxeladol sounds good enough because its as potent as morphine and its safe enough to handle without special precautions unlike some of the ultra potent mu agonists. the racemic mix is what you get if your using regular tramadol for the synthesis.
C-883 is another opioid related to tramadol that is supposedly 3 times as potent as fentanyl. the trans isomer of C-883 is said to be 591 times more potent than morphine and 3.4 times stronger than fentanyl.
Bromadol aka BDPC aka 4-(p-Bromophenyl)-4-(dimethylamino)-1-phenethylcyclohexanol is a tramadol and venlafaxine (effexor) analog that is 10,000 times stronger than morphine!
and there are these ones but they are mixed agonist-antagonists: Ciramadol is a mixed agonist-antagonist tramadol analog that is probably close to hydrocodone in terms of strength, its been said to be stronger than codeine but not as strong as morphine. Profadol is another mixed agonist-anatgonist related to tramadol.
all of the above are not controlled anywhere in the world right now and would be legal to make or have imported. though if the tramadol analogs ever hit the RC market I would hope its faxeladol. faxeladol is also very simple, just 2 steps, to synthesize it from tramadol. the mixed agonists would be safer and less likely to get scheduled but they don't sound that great.