October 2, 2008
I’ve been away for the better part of the last few months, haven’t been able to spend anytime blogging, and I apologize for those of you who have subscribed to the blog and anticipate hearing from me on a regular basis.
During my travels I have had a lot of discussions about ACD/1D NMR Assistant our software tool that has been designed specifically in mind for synthetic and medicinal chemists. Based many of these discussions I feel like I should address this idea of structure verification algorithms in software.
I think the point is NOT to replace the chemists QC or review of their NMR analysis. I know that may be an attractive marketing message…but that’s not the purpose.
A chemist runs an NMR to ensure that their reaction has come to completion, and to confirm that they indeed made what they thought they made. Of course they have other reasons for running NMR (quantitation for example) but this is generally the major reason.
I think there is widespread acknowledgment throughout the industry that the detail and emphasis put into this personal QC varies greatly from chemists to chemist. Some chemists are very diligent in their NMR analysis assigning their data and ensuring that every peak and multiplet makes sense. From my own personal experience as a graduate student and chemist in the industry, I will be honest that for every NMR I ran following a reaction, I didn’t diligently assign every multiplet from every 1H spectrum. If I was in the 3rd or 4th step of a reaction, I was simply looking primarily at 1 or 2 peaks to see if my substitution was successful. If that peak disappeared at 3.1 ppm or that peak appeared at 2.7 ppm…I was off to the next reaction.
Does that make me an irresponsible chemist? Perhaps?…But I keep hearing that this practice is pretty common in the industry. In fact, I’ve had some chemists admit that they don’t look at the NMR at all. If the LC-MS looks good…it’s time to move on.
I think that this is precisely where a tool like 1D NMR Assistant fits in. No, it’s not necessarily smarter than the average chemist, and it’s not necessarily better at assigning data than a chemist. But it can be a valuable tool to complement the chemist’s workflow and help them make better decisions.
Further more….it’s not a black box that tells you whether something is right or wrong.
Here’s an example output from the software:
Note the language:
The structure does not appear consistent with the spectrum.
It is not suggesting that the structure is wrong only that it “appears inconsistent”
This is a key point. It is flagging certain parts of this spectra that perhaps the chemist should spend an additional 10-20 seconds looking at to ensure that they indeed made what they thought they made.It does this because it takes a brute force approach towards the assignment of all protons in the chemical structure to multiplets in the experimental spectrum. If it can’t find a matching multiplet, or the assignment doesn’t make sense…it will tell you.
In some cases these flags may not be serious. Maybe it’s a solvent peak, or a slight impurity, or the software didn’t predict the chemical shift accurately. That’s OK…but the purpose is to alert the chemist that this is one they might want to take a look at. One that might otherwise end up as another false positive in the organizations registration database. Every once in awhile the software will uncover something that might have gotten overlooked.
In addition to being a standard 1D NMR Processing package, it is this functionality that has made 1D NMR Assistant a popular choice early in it’s first year of availability.