So, should I apologize for the tone of yesterday's post? I'm not ready to yet, and I'll explain why.
Here's a general rule: if you find yourself having to make excuses for a scientific paper, for the key experiments that weren't done and the rationales that don't appear, then something is wrong. A paper shouldn't make you have to assume that the authors will get around to running Experiment X and Comparison Y and Test Z, and put that in their next manuscript. (If this makes you think of the recent arsenic bacteria controversy, you're right on target). Anything like that which immediately comes to mind should be in the first manuscript. If the authors haven't put it in there, then it's the job of the referees to tell them to go back and do it. And whoever refereed this paper did an incompetent job.
Now, a quick technical note. It's true that medium-sized rings can form isolable atropisomers in some cases. (An atropisomer, for those who aren't chemists - or chirality geeks - is a compound that can exist as two mirror-image forms just through some sort of constrained movement of its parts. A putatively flat compound that comes around and wraps over itself like a screw thread is one example, as is one with a bond that should be freely rotating but it blocked by large side chains from doing so).
Problem is, this compound sure doesn't look like one of those cases. It has no bulky groups that have trouble getting out of each other's way, and it has no helical chirality. The only thing it has, to my eyes, is a nitrogen that could only lead to new isomers if its barrier to inversion were really, really high - and it shouldn't be. For nevirapine, there really should be no way to isolate such an isomer at room temperature. If anyone can provide evidence for isolable atropisomers in a system as small and lightly substituted as this one, I'll certainly consider eating my words - but not until then.
But that brings up a larger point. This is actually one of the things that makes me think this paper is bogus: the presence of such a compound really would be the big selling point of the manuscript, if the authors had thought about it. Instead, their main focus is on how the structure turns out to be a natural product (which I have trouble believing, too),and not on the bizarre nature of it being chiral. The chirality, frankly, seems to be an afterthought, the way things are written. The word "atropisomer" does not make an appearance. References to the other dibenzo ring systems that have shown this interesting phenomenon (which were worth papers all their own) are not cited. There is no mention of a nitrogen inversion. (If that were the explanation, you'd also expect that heating up the sample would eventually start flipping the molecules past that barrier and removing the optical activity - but there's no mention of any such thing). You'd never know that there was something interesting going on, because the authors give us no reason to believe that they knew that, either.
It would also be quite interesting, if you could have such a thing as an optical isomer of nevirapine, to see what its activity would be on its enzyme target, reverse transcriptase. And if nevirapine could exist as enantiomers, how about running the synthetic material down some chiral columns to see if you could resolve it? Then show that your new optically active stuff is only one of those peaks; that would be pretty convincing. Not done, not done, not even mentioned, etc.
Here's another consideration: as mentioned yesterday, I don't think that this structure has been given very good characterization (the X-ray data seem insufficient to talk about chirality). One of the comments to yesterday's post wondered why the authors didn't show HPLC traces with and without a spike of the authentic drug material. That's an excellent idea, and it's something that would be worth showing in an NMR spectrum, too. Claiming that you found nevirapine in a plant is quite weird - you'd want to really hammer down the fact that everything is identical. But these experiments haven't been done, either.
Allow me to mention one more oddity. The authors actually make reference to "optically active nevirapine" (their footnote #10), but the reference they cite (the original paper from Boehringer Ingleheim) does not, as far as I can see, mention any such thing. And that's because no one has ever mentioned any such thing, and that's because I don't think it exists, outside of (just maybe) a low-temperature NMR experiment.
No, I'm still not buying this. I'm upset with the authors for having proposed such a thing with such thin evidence, but I'm really more upset with the editors of what is supposed to be a reputable journal for publishing it.