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Structural Elucidation – The Cryptic Crossword of the Analytical World

by Leon Vainer, Marketing Communications Specialist, ACD/Labs

Image001Structural Elucidations of NMR spectra, whether combined with other analytical techniques, or on their own, are akin to the challenges of the most complex cryptic crosswords—maybe the kind you find in the weekend editions of The Guardian, or The Times—but much, much tougher with some clues sometimes missing. At least that’s why I believe some of our internal experts and application scientists like the challenges of solving these “puzzles” on a regular basis.

I’ve tried very simple elucidations back in school, and am still trying to solve the occasional cryptic crossword. To be honest, I’m not very good with either. My brain just doesn’t work that way.

So here, I give you one of Dimitris’s, our NMR Business Manager, favorite elucidation. It is complex, challenging and for some, fun!

The Challenge:

Phomopsterone A is a steroid with anti-inflammatory action isolated from a fungus (Phomopsis sp. TJ507A) that grows on a medicinally important plant called Phyllanthus glaucus in Asia. Steroids were always a very difficult challenge for NMR since they have numerous resonances that are very close together. It was not until the late 70s that the 1H NMR spectrum of cholesterol was fully and unambiguously assigned. Even this was only possible using deuterium labelling techniques and the advent of higher field NMR instruments. In fact, cholesterol was always a good example to showcase the power of 2D NMR experiments that were just being developed at the time.

Image002Structure of Phomopsterone A

Fortunately, we are not in 1970, and in the 21st century this task is not as daunting as it was back then. Once the recording of NMR spectra is complete (which may take a few hours) one can feed the data into ACD/Structure Elucidator. The software, in the case of Phomopsterone A, needed just 1 second to combine everything, generate the structures, and rank them according to their relevance with respect to experimental spectra. It is quite a bit of progress, whichever way you look at it. If someone had asked me in 3rd year chemistry to elucidate the structure of a steroid based on NMR spectra as part of my exam, I would have promptly waved the white flag and conceded defeat. Structure Elucidator just needs one second…

Image003

Phomopsterone A. Molecular Connectivity Diagram.

So back to the cryptic crossword analogy… before CASE and ACD/Structure Elucidator, manual elucidation was more like a tough, and sometimes obscure cryptic crossword. With our software, the crossword clue becomes as easy as 3.1415926.

- Leon

PS - If these cryptic crosswords sound intriguing… you can find a bunch here

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