J. Sauri, R.D. Cohen, Y. Liu, M. Reibarkh, A.V. Buevich, R.T. Williamson & G.E. Martin

Transcription

1 1,1-ADEQUATE Exclusively Affords 1 J CC Correlations 1 Bruker NMR User s Meeting SMASH 2016 Well Most of the Time! J. Sauri, R.D. Cohen, Y. Liu, M. Reibarkh, A.V. Buevich, R.T. Williamson & G.E. Martin Merck Research Laboratories, NMR Structure Elucidation Process Research & Development, Rahway, NJ 07065

2 ADEQUATE Nomenclature 1,1-ADEQUATE operates via 1 J CH followed by a 1 J CC transfer. Since this is an outand-back experiment, magnetization goes back along the same coupling pathway to the starting proton for detection. 2 The most prevalent correlation pathways are shown for both experiments. Detection is at the 13 C shift of the remote carbon. 1,n-ADEQUATE also operates via an initial 1 J HC transfer followed by a longrange carbon-carbon transfer via n J CC where n is typically 3, less frequently 2 and only infrequently 4.

3 ADEQUATE Nomenclature The structure shown is 5,6- dihydro lamellarin-h used in the initial development of the ADEQUATE experiments. Examples of the four types of ADEQUATE experiments that were performed on the molecule are shown, colorcoded to the two preceding slides. M. Koch, B. Reif, W. Fenical, C. Griesinger, Tet. Lett., 37, (1996). B. Reif, M. Kock, R. Kerrsebaum, H. Kang, W. Fenical, C. Griesinger, J. Magn. Reson., 118A, (1996). 3 1,1- and 1,n-data are detected at the F1 13 C shift. n,1- and m,n-data are detected at the double quantum frequency of the coupled 13 C resonances.

4 1,1- and 1,n-ADEQUATE pulse sequence Key parameters: 4 1 J CH optimized as in the HSQC experiment with 145 Hz as a typical compromise value. Typical 1 J CC coupling constants range from ~30-75 Hz. Exceptions: cyclopropane ~7-15 Hz cyclobutane ~20-25 Hz nitriles ~95 Hz for CH 2 -CN. ni typically increments. If you need higher resolution allow the resonances to fold in F1.

5 1,1- and 1,n-HD-ADEQUATE What gets decoupled? If the proton-proton coupling to be collapsed arises from a proton on 12 C and the other proton on 13 C, the BIRD element will collapse the coupling. If the proton-proton coupling to be collapsed involves protons that are both on 13 C, homodecoupling does not occur. 5 J. Saurí, W. Bermel, A.V. Buevich, E.C. Sherer, L.A. Joyce, M.H.M. Sharaf, P.L. Schiff, Jr., T. Parella, R.T. Williamson, G.E. Martin, Angew. Chem. Intl. Ed., 54, (2015).

6 Homodecoupling (HD) in 1,1- and 1,n-HD-ADEQUATE 6 Protonated carbons adjacent to a quaternary carbon are collapsed to singlets since the adjacent protons reside on 12 C rather than 13 C and they are consequently refocused by the BIRD pulse with a commensurate increase in s/n. Protonated carbon correlations to adjacent protonated carbons are not collapsed since both protons reside on 13 C and are hence unaffected by the BIRD pulse.

7 How 1,n-HD-ADEQUATE works: ALL n J CC correlations are effectively homodecoupled in the 1,n-HD- ADEQUATE experiment. 5 J HH Couplings are typically too small to be resolved. Couplings to the proton used to detect the n J CC will be from protons on 12 C and will be decoupled. 7

8 Amplitude Transfer as a Function of 1 J CC Optimization 1 J CC optimization Hz Curves shown are calculated for a range of potential 1 J CC coupling constants. Response intensity is a function of the congruence of the actual coupling constant to the optimization. Correlations involving either very small or very large 1 J CC couplings will be problematic with standard optimization of Hz. 8

9 Structures with 1,1-ADEQUATE The indeterminate nature of n J CH HMBC correlations precluded unequivocal determination of the structure. Top candidate structures from ACD Structure Elucidator calculation were equally probable. 1,1- and 1,1-HD-ADEQUATE experiments were performed. C. Lorenc, J. Saurí, A. Moser, A.V. Buevich, A.J. Williams, R.T. Williamson, G.E. 9 Martin, M.W. Peczuh, ChemistryOpen, 4, (2015),

10 Alternative Structures based on Mechanistic & CASE Considerations 1 2 Proposed structures, 1 and 2, from mechanistic considerations are shown above. The two top structures from Computer-Assisted Structure Elucidation (CASE) were 1 (above) and

11 Structures with 1,1-ADEQUATE 1 11 Both conventional 1,1- and 1,1-HD-ADEQUATE data were acquired. Bold red bonds were defined by ADEQUATE Black arrows Key correlations from 2 Hz optimized LR-HSQMBC

12 1,1-ADEQUATE 1 J CC correlations: Well, most of the time anyway! noise O O O 11 O O 10 O 9 8 OH 2 J CC coupling between C13-C11 measured with a J-modulated ADEQUATE experiment O 5 O C. Lorenc, J. Saurí, A. Moser, A.V. Buevich, A.J. Williams, R.T. Williamson, G.E. Martin and M. W. Peczuh, ChemistryOpen, 4, (2015).

13 2 J CC Intensity vs. 1 J CC Optimization 20Hz 30Hz 40Hz 50Hz 60Hz Hz The intensity of 2 J CC correlations will depend on 1 J CC optimization of the experiment. Calculated 2 J CC = 12.8 Hz; measured = 11.3 Hz. 13

14 Cryptospirolepine: Key 1,1-HD-ADEQUATE Correlations: Experiment was optimized for 60 Hz. The 2 J CC coupling from C13 to C1/C11 was calculated (DFT) to be 15.4 Hz, which would give a calculated intensity of 0.16 in this experiment. 14

15 More carbonyl problems 1 H NMR Conventional 1,1-ADEQUATE (40 Hz) 15 J. Saurí, Y., Liu, R.T. Williamson, G.E. Martin, Magn. Reson. Chem., 54, (2016); DOI: /mrc4385.

16 More carbonyl problems 9.9 Hz J-modulated 1,1-ADEQUATE 16.3 Hz The DFT calculated 2 J CC coupling from H4 to C1 was 11.2 Hz and the coupling from the H3 -methylene to C1 was 16.7 Hz. 16 For a 40 Hz optimized 1,1-ADEQUATE, the 11.2 Hz 2 J CC correlation from C4 to C1 had a calculated response intensity of 0.19 while the larger 16.7 Hz 2 J CC correlation from C3 to C1 would be expected to give a correlation with an intensity of 0.37

17 Correlations that aren t quite what they appear! Photocatalyzed hydroxymethylation that produced a single isomer (2 or 3) in 32% isolated yield Objective: Determine CH 2 OH position for reaction product. Structure 1 unequivocally characterized by 2D methods (COSY, HSQC, 1 H- 13 C and 1 H- 15 N HMBC, ROESY) and HRMS measurements..

18 Correlations that aren t quite what they appear! 1,1-ADEQUATE Spectrum J-Modulated 1,1-ADEQUATE spectrum 1,1-ADEQUATE appears to show a one-bond correlation from C5 to C2 and three-bond correlation from C5 to C6, which would point to structure 3 as being correct. Disagreement with DFT calculations!! C5-C6 correlation is a 1 J CC while C5 to C2 is a 3 J CC, which is the opposite of the conclusion drawn from interpretation of the 1,1-ADEQUATE This data points to structure 2 as being correct. R. D. Cohen, J. Saurí C.A. Huff, S.W. Krska, G.E. Martin, Magn. Reson. Chem DOI: /mrc.4470

19 Correlations that aren t quite what they appear! Note the near isochronous chemical shifts for carbons C5 and C6, which indicates an AB 13 C- 13 C spin system. R. D. Cohen, J. Saurí, C.A. Huff, S.W. Krska, G.E. Martin, Magn. Reson. Chem DOI: /mrc.4470

20 Correlations that aren t quite what they appear! Expt Predicted Predicted Expt Atom # d (ppm) d (ppm) d (ppm) Coupling J (Hz) J (Hz) J (Hz) C C2-C C C2-C C C2-C C C3-C rms: C3-C C5-C DFT predictions of chemical shifts and coupling constants were entirely consistent with the measured experimental data for structure 2. R. D. Cohen, J. Saurí, C.A. Huff, S.W. Krska, G.E. Martin, Magn. Reson. Chem DOI: /mrc.4470

21 Correlations that aren t quite what they appear! INADEQUATE (blue) and 1,1-ADEQUATE (green) correlations. The red dotted correlation was expected but missing in the INADEQUATE spectrum due to a pronounced strong coupling effect: 1 J C5,C6 > δ C5 δ C6. 21 Strong (AB) couplings are relatively rare in 13 C NMR due to the larger chemical shift range compared to proton.

22 Other Problematic Correlations Observed in 1,1-ADEQUATE Spectra Category Example Type of Large Multi-Bond J CC Typical Size pyrazine 3 J CC 10 Hz ketone 2 J CC 10 Hz pyrimidine 3 J CC 15 Hz pyridine 3 J CC 10 Hz 22

23 Summary 1,1-ADEQUATE spectra have traditionally been assumed to provide only 1 J CC correlations equivalent to 2 J HC HMBC correlations. 2 J CC and 3 J CC correlations can be observed in 1,1- and 1,1-HD-ADEQUATE spectra even when optimized for Hz. DFT Calculations provide a good reality check. NMR groups should be doing this on a regular basis. Unfortunately, most don t! 23

24 We should pursue our science with the same passion That we pursue doing whatever we enjoy in our lives! Thank you!

25 J-modulated HD-ADEQUATE The green highlighted segment of the pulse sequence contains the J-scaling module. 1 J CC Coupling constants are typically upscaled by a factor of Κ = 10; n J CC coupling constants should be upscaled by Κ = to facilitate measurement. BIRD-based homodecoupling is implemented in the blue-shaded segment of the pulse sequence. Typically setting l0 = 8 is optimal. 25