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Our article Structure Revision of Asperjinone Using Computer-Assisted Structure Elucidation Methods

Our article “Structure Revision of Asperjinone Using Computer-Assisted Structure Elucidation Methods”, is now available on the Journal of Natural Products website here.

ACS_paper

This was a long time coming…almost a year in the review process and iterations. I continue to see the reports from many publishers about how fast articles are published but my experience in 2012 is that it is many months past the published averages! The primary hurdles appear to be the speediness of reviewers and the willingness of editors to pursue them! When I ask for updates the general response is “We will contact the reviewers…”

The URL http://pubs.acs.org/articlesonrequest/AOR-IKzXYYSAAQCbXVAc4Fva can be used for us to distribute 50 e-prints of the article so please feel free to grab one. Details below…

“As part of the ACS Articles on Request e-prints service, ACS authors may choose to e-mail or post this link on their website to distribute up to 50 free e-prints of their final published articles to interested colleagues during the first 12 months of publication. After that 12-month period, any author’s article may be accessed without restriction via the same author-directed link that appears above. The link seamlessly directs subscribers to the full text version of the article on the ACS Publications website.”

 

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Our Contributions to the Literature Regarding Computer-Assisted Structure Elucidation

When writing a publication how many of us conduct complete literature searches? For those of us who do not have access to Scifinder how are we finding our literature? Probably through Google Scholar? When I write a paper I admit that some of my searches may be less than complete but I do try and stay informed in regards to what is going on in my domain. VERY occasionally I get feedback from reviewers pointing me to references that they feel I either ignored or was unaware of. Many times they are co-authored by the reviewer themselves…and it is pretty easy to figure out who the reviewers are ūüôā

Today I received an email in my inbox about the latest article in the Journal of Cheminformatics.¬†It is¬†OMG: Open Molecule Generator. The article is¬†here.¬†¬†The abstract opens with “Computer Assisted Structure Elucidation has been used for decades to discover the chemical structure of unknown compounds. In this work we introduce the first open source structure generator, ¬†Open ¬†Molecule ¬†Generator ¬†(OMG), ¬†which ¬†for ¬†a ¬†given ¬†elemental ¬†composition produces ¬†all ¬†non-isomorphic ¬†chemical ¬†structures ¬†that ¬†match ¬†that ¬†elemental ¬†composition.”

Having been involved with Computer-Assisted Structure Elucidation for many years, having co-authored a book about it (here) and probably the definitive review article from the past 5 years (here) I would have assumed that our work would have been referenced. I was surprised to see that our work was not referenced while other CASE systems were. Articles we’ve issued over the past few years are below. I’ve gathered them here to point the authors to in case they want to reference any of them and missed them in the literatire search.

I am taking advantage of the fact that I can leave comments on the provisional manuscript¬†here¬†(what a great capability!!!) and will let them know about this list. it would be good to compare the performance of the OMG with the structure generator under ACD/Structure Elucidator sometime….

 

1) M.E. Elyashberg, K.A. Blinov and A.J. Williams, Computer-aided Molecular Structure Elucidation on the Basis of 1D and 2D NMR Spectra, Applied Magnetic Resonance, (May 2000)

2) K.A. Blinov, M.E. Elyashberg, S.G. Molodtsov, A.J. Williams and E.R. Martirosian, An Expert System for Automated Structure Elucidation Utilizing 1H-1H, 13C-1H, and 15N-1H 2D NMR correlations, Fresenius J. Anal. Chem., 369, 709 (2001)

3) G.E. Martin, C.E. Hadden, D.J. Russell, B.D. Kaluzny, J.E. Guido, W.K. Duholke, B.A. Stiemsma, T.J. Thamann, R.C. Crouch, K.A. Blinov, M.E. Elyashberg, E.R. Martirosian, S.G. Molodtsov, A.J. Williams, P.L. Schiff, Jr., Identification of Degradants of a Complex Alkaloid Using NMR Cryoprobe Technology and ACD/Structure Elucidator, J. Heterocyclic Chem. 39, 1241 (2002)

4) M.E. Elyashberg, K.A. Blinov, A.J. Williams, E.R. Martirosian, S.G. Molodtsov, Application of a New Expert System for the Structure Elucidation of Natural Products from the 1D and 2D NMR Data, J. Nat. Prod., 65, 693 (2002)

5) G . E. Martin, C .E. Hadden, D. J. Russell, B. D. Kaluzny, J. E. Guido, W. K. Duholke, B. A. Stiemsma, T. J. Thamann, R. C. Crouch, K. A. Blinov, M. E. Elyashberg, E. R. Martirosian, S. G. Molodotsov, A. J. Williams, and P. L. Schiff, Jr., Identification of Degradants of a Complex Alkaloid Using NMR Cryoprobe Technology and ACD/Structure Elucidator, J. Heterocyclic Chem., 39 1241-1250 (2002).

6) K. A. Blinov, D. Carlson, M. E. Elyashberg, G. E. Martin, E. R. Martirosian, S. Molodtsov, and A. J. Williams, Computer-Assisted Structure Elucidation of Natural Products with Limited 2D NMR Data: Applications of the StrucEluc System, Magn. Reson. Chem., 41, 359-372 (2003).

7) G. E. Martin, D. J. Russell, K. A. Blinov, M. E. Elyashberg and A. J. Williams, Applications and Advances in Cryogenic NMR Probes & Computer-Assisted Structure Elucidation. Ann. Magn. Reson., 2, 1-31 (2003)

8)¬†K. Blinov, M. Elyashberg, E. R. Martirosian, S. G. Molodtsov,¬†A. J. Williams, M. H. M. Sharaf, P. L. Schiff, Jr., R. C. Crouch, G. E. Martin, C. E. Hadden, and J. E. Guido, ‚ÄúQuindolinocryptotackieine: The Elucidation of a Novel Indoloquinoline Alkaloid Structure through the Use of Computer-Assisted Structure Elucidation and 2D-NMR,‚Ä̬†Magn. Reson. Chem.,¬†41, 577-584 (2003).

9) M. E. Elyashberg, K. A. Blinov, E. R. Martirosian, S. G. Molodtsov,¬†A. J. Williams, and G. E. Martin, Automated Structure Elucidation ‚Äď The Benefits of a Symbiotic Relationship between the Spectroscopist and the Expert System,¬†J. Heterocyclic Chem.,¬†40, 1017-1029 (2003).

10) M. E. Elyashberg, K. A. Blinov, A. J. Williams, S. G. Molodtsov, G. E. Martin, and E. R. Martirosian, Structure Elucidator: A Versatile Expert System for Molecular Structure Elucidation from 1D and 2D NMR Data and Molecular Fragments, J. Chem. Inf. Comput. Sci. 44, 771-792 (2004).

11) S. G. Molodtsov, M. E. Elyashberg, K. A. Blinov, A. J. Williams, E. E. Martirosian, G. E. Martin, and B. Lefebvre. Structure Elucidation from 2D NMR Spectra Using the StrucEluc Expert System: Detection and Removal of Contradictions in the Data. J. Chem. Inf. Comp. Sci., 44, 1737-1751 (2004)

12) G. J. Sharman, I. C. Jones, M. P. Parnell, M. C. Willis, M. F. Mahon, D. V. Carlson, A. J. Williams, M. E. Elyashberg, K. A. Blinov, S. G. Molodtsov. Automated structure elucidation of two products in a reaction of an a,b-unsaturated pyruvate. Magn. Reson. Chem. 42, 567 (2004)

13) Y. D. Smurnyy, M. E. Elyashberg, K. A. Blinov,  B. A. Lefebvre, G. E. Martin, and A. J. Williams, Computer-Aided Determination of Relative Stereochemistry and 3D Models of Complex Organic Molecules from 2D NMR Spectra, Tetrahedron, 61, 9980-9989 (2005).

14) M. E. Elyashberg, K. A. Blinov, A. J. Williams, S. G. Molodtsov, and G. E. Martin, Are Deterministic Expert Systems for Computer-Assisted Structure Elucidation Obsolete? J. Chem. Inf. Model. 46, 1643-1656 (2006).

15) M. E. Elyashberg, K. A. Blinov, S. G. Molodtsov, A. J. Williams, and G. E. Martin, Fuzzy Structure Generation: An Efficient New Tool for Computer-Aided Structure Elucidation (CASE), J. Chem. Inf. Model., 47, 1053-1066 (2007). 10.1021/ci600528g

16) M. E. Elyashberg, A. J. Williams, and G. E. Martin. Computer-Assisted Structure Verification and Elucidation Tools In NMR-Based Structure Elucidation. Review article. Progress in NMR Spectroscopy (2007) 10.1016/j.pnmrs.2007.04.003 

17) Y. D. Smurnyy, K. A. Blinov, T. S. Churanova, M. E. Elyashberg, and A. J. Williams. Toward More Reliable 13C and 1H Chemical Shift Prediction: A Systematic Comparison of Neural-Network and Least-Squares Regression Based Approaches, J. Chem. Inf. Model.  48, 128-134, (2008)

18) M. E. Elyashberg,¬†A. J. Williams, D. C. Lankin, G. E. Martin, J. Porco, W. F. Reynolds, and C. Singleton, Applying Computer-Assisted Structure Elucidation Algorithms for the Purpose of Structure Validation ‚Äď Revising the NMR Assignments of Hexacyclinol,¬†J. Nat. Prod.,¬†71, 581-588 (2008).

19) M.E. Elyashberg, K.A. Blinov and A.J. Williams, A Systematic Approach for the Generation and Verification of Structural Hypotheses. Magn. Reson. Chem. 47, 371-389, (2009)

20) M. E. Elyashberg, A. J. Williams, and K.A. Blinov, The Application of Empirical Methods of 13C NMR Chemical Shift Prediction as a Filter for Determining Possible Relative Stereochemistry. Magn. Reson. Chem. 47, 333-341 (2009)

21) Y. D. Smurnyy, K. A. Blinov, T. S. Churanova, M. E. Elyashberg, and A. J. Williams. Development of a fast and accurate method of 13C NMR chemical shift prediction. Chemometrics and Intelligent Laboratory Systems, 97(1), 91-97, (2009)

22) M. E. Elyashberg, A. J. Williams and K. A. Blinov, Structural revisions of natural products by Computer Assisted Structure Elucidation (CASE) Systems, Nat. Prod. Rep., 2010, DOI: 10.1039/c002332a

23) Blind trials of computer-assisted structure elucidation software, Journal of cheminformatics 4 (1), 5, A Moser, ME Elyashberg, AJ Williams, KA Blinov, JC DiMartino

24) ¬†Elucidating ‚Äėundecipherable‚Äôchemical structures using computer‚Äźassisted structure elucidation approaches, Mikhail Elyashberg, Kirill Blinov, Sergey Molodtsov, Antony Williams,¬† ¬†Magnetic Resonance in Chemistry,¬†50(1), ¬†22‚Äď27, ¬†2012¬†DOI:¬†10.1002/mrc.2849

BOOK: Contemporary Computer Assisted Approaches to Molecular Structure Elucidation by Kirill Blinov, Mikhail Elyashberg and Antony J. Williams, Royal Society of Chemistry

 

 

 

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Our book published Contemporary Computer-Assisted Approaches to Molecular Structure Elucidation

Almost two years of work, a collaboration and friendship developed over many years of my tenure at Advanced Chemistry Development¬†(with Mikhail Elyashberg and Kirill Blinov),¬†a story about a decade of work to develop what we believe is the world’s premier Computer Assisted Structure Elucidation software, and multiple iterations later, our book is now at the printers.

Our Book COver

Our book is “Contemporary Computer-Assisted Approaches to Molecular Structure Elucidation” and is already listed on Amazon here.

“Computer Assisted Structure Elucidation (CASE) systems are powerful software applications capable of outperforming human data interpretation in terms of both speed and reliability. They combine software algorithms with tools for molecular structure elucidation using spectroscopic data. This book describes the principles on which CASE systems are based and concisely explains the algorithmic concepts behind the programs. It puts the technique in the context of its origins and describes the challenges that have been overcome to produce modern CASE systems. It uses the authors’ software development experience to discuss the present state-of-the-art and explains how the synergistic marrying of man and machine can provide superior results. Readers will gain a firm grounding in the fundamentals of CASE, an understanding of the challenges associated with algorithms, and an appreciation of the technologies underlying NMR prediction and structure verification. Scientists who have never used CASE systems before will find all the information necessary to master this new and very effective approach. Those with some experience will benefit from details on the latest developments.”

I willingly admit I’m glad it’s over…it feels great to have it finished, great to know its at the printers and good to know that we have likely written the definitive volume in this area for the time being. Now time to let my eyes recover before getting back to writing two more volumes about NMR applied to Natural Products, to be released next year all being well!

 

 

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How are NMR Prediction Algorithms and AFM Related?

There’s a really nice News piece over on Nature News regarding “Feeling the Shapes of Molecules“. The work reports on how Atomic Force Microscopy is being used to deduce chemical structure directly, one molecule at a time. It is, quite simply, stunning. This work is an extension of the original work reported on pentacene that many scientists thought was spectacular. This work is even one step closer to the dream of single molecule structure identification. The work is entitled “Organic structure determination using atomic-resolution scanning probe microscopy” and as well as the IBM group responsible for the AFM work involves Marcel Jaspars, someone who’s work I have watched for many years as I am trained as an NMR spectroscopist and have spent a lot of time working on computer-assisted structure elucidation (CASE) approaches to examine natural product structures (see references in here…).

The molecule that they studied was cephalandole A¬† that had previously been mis-assigned. Interestingly my old colleagues from ACD/Labs, where I worked for over a decade, and myself had published an article in RSC’s Natural Product Reviews where we studied “Structural revisions of natural products by Computer-Assisted Structure Elucidation (CASE) systems“. The basic premise of the article is that there are incorrect structures making it into the literature because of the misinterpretation of the analytical data and that computer algorithms, specifically NMR prediction and CASE algorithms, can be used to rule out structures elucidated by the scientists.It is hard to do justice to the entire review article as we detail the approaches to CASE and NMR prediction and doing it in a blog post is tough. So, I do recommend reading the NPR article. However, I am extracting the part that applies to the elucidation of the structure of cephalandole A and how algorithms would be of value in negating the incorrect structure.

“In 2006 Wu et al isolated a new series of alkaloids, particularly cephalandole A, 16. Using 2D NMR data (not tabulated in the article) they performed a full 13C NMR chemical shift assignment as shown on structure 16.

Mason et al synthesized compound 16 and after inspection of the associated 1H and 13C NMR data concluded that the original structure assigned to cephalandol A was incorrect. The synthetic compound displayed significantly different data from those given by Wu et al. The 13C chemical shifts of the synthetic compound are shown on structure 16A.

Cephalandole A was clearly a closely related structure with the same elemental composition as 16, and structure 17was hypothesized as the most likely candidate. Compound 17 was described in the mid 1960s and this structure was synthesized by Mason et al.The spectral data of the reaction product fully coincided with those reported by Wu et al. The true chemical shift assignment is shown in structure 17. For clarity the differences between the original and revised structures are shown in Figure 17.

We expect that 13C chemical shift prediction, if originally performed for structure 16, would encourage caution by the researchers (we found dA=3.02 ppm).Figure 18 presents the correlation plots of the 13C chemical shift values predicted for structure 16 by both the HOSE and NN methods versus experimental shift values obtained by Wu et al. The large point scattering, the regression equation, the low R2 =0.932 value (an acceptable value is usually R2 ‚Č• 0.995) and the significant magnitude of the g-angle between the correlation plot and the 45-grade line (a visual indication for disagreement between the experiment and model) could indicate inconsistencies with the proposed structure and should encourage close consideration of the structure.Our experience has demonstrated that a combination of warning attributes can serve to detect questionable structures even in those cases when the StrucEluc system is not used for structure elucidation.

Figure 18. Correlation plots of the 13C chemical shift values predicted for structure 16 by HOSE and NN methods versus experimental shift values obtained by Wu et al. Extracted statistical parameters: R2(HOSE)=0.932, dHOSE=1.20dexp-25.6.

So, for those NMR jocks who don’t have access to the genius of IBM scientists performing AFM, and yet want to have tools to help in the elucidation process you’d be doing well to use NMR prediction algorithms and CASE systems to help….it’s rather embarrassing to have to issue a retraction on a paper with your name on.

Meanwhile I am in awe of the work reported by Marcel and his colleagues at IBM. Clearly there’s a long way to go before such approaches are mainstream but the flag is in the sand…this is where things will speed up and we are surely destined, I hope (!) to see many more reports of this type of work and how it is progressing. Let’s hope. Feedback on the NPR article welcomed!!!

Organic structure determination using atomic-resolution scanning probe microscopy

 

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