Technical Note

Creating an 13C/13C TOCSY Experiment from an HSQC/TOCSY Dataset

ACD/2D NMR Processor Version 9.06

Arvin Moser Advanced Chemistry Development, Inc.

Toronto, ON, Canada www.acdlabs.com

Introduction

While a 1H/1H COSY or TOCSY can be a challenge for a structure with severe spectral overlaps and thus difficult to interpret, obtaining an HSQC/TOCSY can be a better choice.

Converting data from one form to another can be as common as Fourier Transforming from the time domain to the frequency domain. Stepping from an HSQC/TOCSY (or HMQC/TOCSY) to a 13C/13C TOCSY [1,2], an NMR Spectroscopist can directly extract information about the carbon-carbon framework (the 13C/13C TOCSY data represents contiguous protonated carbons). The data can then be automatically assigned to produce a match factor or pass the information to ACD/Structure Elucidator [3].

This paper will show how to process a raw HSQC/TOCSY dataset [4,5] and obtain a 13C/13C TOCSY for cyclopentafuranone (IUPAC: (3aR,4S,5R,6aS)-5-hydroxy-4-(hydroxymethyl)hexahydro-2H-cyclopenta[b]furan-2-one) (1).

O

O

OH

OH

1

For further details about ACD/Labs’ recent work in the area of applications of Indirect Covariance processing, and to obtain a detailed description of the matrix manipulations underlying the processing algorithms, the readers are referenced to our literature article [6].

Processing Raw NMR Data

The dataset IDR–gHSQC/TOCSY [3] (IDR = Inverted Direct Response) is imported into ACD/2D NMR Processor [7] as shown in Figure 1. Clicking the Full FT button will use the default processing parameters stored by the instrument software stored in the file.

Technical Note

Figure 1: Raw IDR–gHSQC/TOCSY NMR dataset acquired with a delay of 18 msec.

A forward Linear Prediction is applied along the t1 (see Figure 2) prior to Fourier Transforming the data. Linear Prediction could be useful for unsymmetrical covariance processing where digitization in F2 needs to be identical.

2

Technical Note

Figure 2: Linear Prediction dialog box and the parameters used along the t1.

The correctly phased 1H and 13C NMR spectra are transferred to the 2D experiment so that proper F2 and F1 phasing information is already present. This may also generally assure that the direct responses were correctly phased in an IDR-gHSQC/TOCSY experiment. The dataset is phased and baseline corrected. A structure can be attached to the experiment at this stage or later on. The structure is needed for verification to be performed and for automatic peak assignment.

3

Technical Note

Figure 3: Processed 2D NMR dataset with 1D NMR spectra setup and accompanied structure transferred from ACD/ChemSketch [8]. Negative correlations (shown in blue) represent the direct HSQC component and the positive correlations (shown in red) represent the TOCSY component. Contour color selection can be chosen to the user’s preference or to match the convention of the user’s spectrometer.

From the menu toolbar, select Process, then Indirect Covariance NMR. The square root of the spectrum is accomplished as part of Indirect Covariance NMR.

4

Technical Note

Figure 4: Applying Indirect Covariance NMR as selected from the menu toolbar.

The direct domain is converted from a 1H to a 13C and the attached 13C NMR is automatically transferred to the direct domain. The diagonal correlations indicate the protonated carbons and the off-diagonal peaks correlate the diagonal peaks.

5

Technical Note

Figure 5: Converted 13C/13C TOCSY spectrum. Positive correlations along the diagonal (shown in red) represent the direct HSQC component and the positive correlations (shown in blue) represent the TOCSY component. The positive off-diagonal correlations are artifacts produced from overlapping proton signals.

Automatic Peak picking is performed followed by automatic structure-to-spectrum verification and automatic peak assignment for both the direct and indirect correlations.

6

Technical Note

Figure 6: Auto-Peak Picked 13C/13C TOCSY spectrum. The positive off-diagonal correlations (red) at (56, 40) and (40, 56) ppm are artifacts produced from overlapping proton signals and are not considered in the verification and assignment.

Once the data has been converted, assignment is performed using the ACD/2D NMR Predictors housed in 2D NMR Processor. The peaks are assigned and displayed by the peak label and the assigned atoms are displayed in green. The data can then be reported and stored in Microsoft® Word or PowerPoint, or stored in a lab notebook for future reference.

7

Technical Note

Figure 7: With the Verification and Assignment, a 2D HSQC/TOCSY is predicted and subsequently utilized for assigning the experimental correlations.

Figure 8: The result of Verification for the 2D HSQC/TOCSY for 1 provides a Match Factor criteria to judge automatic assignment of the experimental correlations. A “good” result is determined by a Spectrum Match Factor over 0.7.

8

Technical Note

Figure 9: The assigned spectrum shows picked peaks with the assignment indicated in brackets. In addition, the assigned atoms on the structure are shown in green for a quick visual for scrutinizing assignments. Hovering over the assigned atom highlights the corresponding correlations for a quick reference.

9

Technical Note

Figure 10: In addition to assigning peaks, correlations arrows are displayed for the off-diagonal information. The correlation arrows are fully adjustable and vary in colour depending on the bond separation (not shown as all correlations correspond to 1J).

10

Technical Note

Figure 11: Finally, report the results with a custom template or as a standard report with ACD/ChemSketch showing the company logo, structure with correlation arrows, Match Factors, and Table of Assignment. This report can then be passed to Microsoft Word or other textual products.

Conclusion

Following the above steps for Indirect Covariance NMR, an HSQC/TOCSY (or HMQC/TOCSY) can be visually transformed and interpreted as a 13C/13C TOCSY.

For more information on ACD/2D NMR Processor, consult the ACD/2D NMR Processor Tutorial and Reference Manual.

References

1. N.Trbovic, S. Smirnov, F. Zhang, and R. Brüschweiler, Covariance NMR Spectroscopy by Singular Value Decomposition J. Mag. Res., 171, 277-283 (2004).

2. F. Zhang, and R. Brüschweiler, Indirect Covariance NMR Spectroscopy J. Amer. Chem. Soc., 126, 13180-13181 (2004).

3. ACD/Structure Elucidator. http://www.acdlabs.com/structureelucidator/. August 3, 2005.

11

Technical Note

4. C. E. Hadden, G. E. Martin, J.-K. Luo, and R. N. Castle, A Comparison of the Hyphenated Experiments GHMQC-TOCSY and GHSQC-TOCSY J. Heterocyclic Chem., 36, 533-539 (1999).

5. C. E. Hadden, G. E. Martin, J.-K. Luo, and R. N. Castle, 1H and 13C Spectral Assignment of Naphtho[2',1':5,6]naphtho[2',1':4,5]thieno[2,3c]quinoline Using the IDR-GHSQC-TOCSY Experiment J. Heterocyclic Chem., 37, 821 (2000).

6. K. A. Blinov, N. I. Larin, M. P. Kvasha, A. Moser, A. J. Williams, and G. E. Martin, Analysis and Elimination of Artifacts in Indirect Covariance NMR Spectra via Unsymmetrical Processing, Mag. Res. Chem. In press (2005).

7. ACD/2D NMR Processor. http://www.acdlabs.com/2dnmrproc/. August 3, 2005.

8. ACD/ChemSketch. http://www.acdlabs.com/chemsketch/. August 3, 2005.

12