
Jordan AD, Orsini MJ, Middleton SA et al. (2005) 8-(Heteroaryl) phenalkyl-1-phenyl-1, 3, 8-triazaspiro[4.5]decan-4-ones as opioid receptor modulators. Med Chem 1:601–610
I haven't calculated the pKa or LogP of this compound but simpler derivatives are covered by:
E. K. Fifer, W. M. Davis, and R. F. Borne, Bur. 1. Med. Chem. 19, 519 (1984).
Now the simpler compounds have a chiral methyl side-chain on the N-benzyl and their potency is x450 pethidine.
These compounds are discussed in 'Opioid Analgesics: chemistry and receptors' by Casy & Parfitt. This work, along with 'Opiates' by R.lenz et al are really vital pieces of work. Even so, there are whole classes of opioids that they don't cover. I've come across some unexpectedly potent opioids. That is what makes opioid chemistry so interesting. The sheer volume of different compounds means it is almost impossible to cover them all and it's very hard for anyone to read the IUPAC and devine the activity.
Many moons ago someone mentioned a new delta/kappa opioid (with reference) that had a secondary amine and an amide. It was open-chain and looked worth more examination but I've lost the paper.
I will finish by noting that BDPC is turning up. From what I have read, it's quite good for 4 hours then just odd for 8 hours. I suspect that it's due to N-demethylation. Why people didn't simply make the p-Me homologue, I don't know. That methyl offers a convenient point for the body to metabolize the material an so while duration is shorter, the action is positive, not mixed.