Two-Dimensional NMR Spectroscopy

Transcription

1 Two-Dimensional NMR Spectroscopy Applications for Chemists and Biochemists Second Edition Expanded and Updated to Include Multidimensional Work EDITED BY William R. Croasmun and Robert M. K. Carlson VCH

2 Contents 1. Introduction to Multidimensional NMR Methods 1 George A. Gray 1.1 Introduction What Are the Benefits of Multidimensional NMR? Can It Be Painless? How and Why Does Multidimensional NMR Work? Preparation Evolution Mixing Detection How Does the Detection Process Work? How Do Pulses Affect Nuclear Spins? The Rotating Frame of Reference The 90 Pulse Precession in the xy Plane Refocusing Pulses Simultaneous A and X 180 Pulses in an AX Coupled System Nonobservable Magnetization and Mixing of Spin States by 90 Pulses Polarization Transfer Pulses Pulsed-Field Gradients 24 ix

3 CONTENTS Spin-Locking Pulses Selective 2D or 1D Versions of Multidimensional Experiments The General Multidimensional NMR Experiment Practical Details for the General 2D NMR Experiment Display Modes Data Processing Can I Use What I Already Know About NMR in 2D NMR? Can I Use /-Coupling Information? Data Output in 2D /-NMR Sensitivity in 2D /-NMR How Can I Emphasize Long-Range Coupling Information? How Can I Correlate Protons That Are Coupled to Each Other? Data Display and Output How Large a Coupling is Necessary to Produce a Cross Peak? But What About the Very Small Coupling? How Can I Simplify a Very Crowded COSY Spectrum? Can I Use the Spreading Power of,3 C to Understand My Proton Spectrum? How Do I Interpret a HETCOR Spectrum? Can I Correlate My Carbons with Protons Other Than the Bonded Ones? What About Other Nuclei? Is There Any Way to Relate Three Nuclei at Once? How Can I Learn About Nuclei That Are Not Coupled? How Can I Study Relaxation in My Mid-sized Molecule? The Protons Are Reaily Peripheral to the Carbon Skeleton. How Can I Directly Determine the Carbon Bonding Framework in My Molecule? My Sample Is Too Small to Use l3 C-Detected Heteronuclear 2D Shift-Correlation or Double-Quantum Connectivity. Can I Still Get Connectivity Information for Nuclei Other Than Protons? Conclusion 64 Acknowledgment 64 References 65

4 CONTENTS xi 2. Experimental Aspects of Two-Dimensional NMR 67 William E. Hüll 2.1 Introduction: A Continuing Revolution Technical Developments in Multidimensional NMR Spectrometer Hardware Data System Software and Off-Line Processing Basic Principles and Spectrometer Calibration Procedures Pulse Power and Off-Resonance Effects Probehead Tuning Pulse Calibration Radiation Damping Sensitivity Tests Phase Shifting The Quadrature Receiver Specialized Techniques and Procedures Composite Pulses for Decoupling (CPD) and for Cross Polarization Composite Pulses for Multipulse Sequences Solvent Suppression Methods Selective Excitation Field-Gradient Pulses Preparatory 1D Experiments Sample Preparation Temperature Control and Shimming D Reference Spectra Effects of Relaxation Optimization of 2D Spectral Widths Basic Aspects of 2D Experiments Formalism of Multidimensional NMR D Data Acquisition D Imperfections D Data Processing Homonuclear 2D Experiments J-Resolved 2D Shift Correlation via One-Step Coherence Transfer Multistep Coherence Transfer (RELAY) Coherence Transfer by Isotropie Mixing (TOCSY, HOHAHA) Shift Correlation via Incoherent Interactions Multiple-Quantum Spectroscopy Hybrid 2D Techniques for Relayed Coherence Transfers 356

5 xii CONTENTS Solvent Suppression in 2D NMR D and Soft 2D Methods Using Selective Pulses Homonuclear 2D Using Gradient Echoes What Lies Beyond 2D? Heteronuclear 2D Experiments Nomenclature and General Principles Heteronuclear 7-resolved 2D NMR Heteronuclear Shift-correlated 2D NMR Heteronuclear Shift Correlation with Elimination of Proton-Proton Couplings Heteronuclear Shift Correlation via Long-Range Couplings Heteronuclear Shift Correlation via Dipolar Interactions Heteronuclear Relayed Coherence Transfer and Hybrid Experiments X-Filters for Discrimination of Protons Bound to NMR-Active Isotopes Heteronuclear MQC Heteronuclear J Cross Polarization D Analogs of Heteronuclear 2D Experiments Use of B 0 Field Gradients in Heteronuclear Spectroscopy Closing Remarks 423 References Proton-Detected Heteronuclear and Multidimensional NMR 457 Christian Griesinger, Harald Schwalbe, Jürgen Schleucher, and Michael Sattler 3.1 Introduction Sensitivity Resolution Suppression of Unwanted Signals Product Operator Formalism Amplitude and Phase Modulation Phase Cycles Multiple Quantum Filters Basic Experiments HMQC (Heteronuclear Multiple-Quantum Correlation), HMBC (Heteronuclear Multiple-Bond Correlation) 474

6 CONTENTS xui HSQC (Heteronuclear Single-Quantum Correlation) Double INEPT Sensitivity-Enhanced Correlation Simultaneous Correlation to Several Heteronuclear Spins Constant-Time Experiments Editing Accessories Folding Non-FT Methods for Processing Bilinear Rotations Gradients Filters Decoupling Calibration of Pulses D Methods Homonuclear 3D Experiments Assignment-oriented Heteronuclear 3D NMR Heteronuclear 3D with l5 N/ l3 C-labeled Biomolecules: Backbone Assignment Sidechain Assignments Combinations Between Backbone and Sidechain Assignments Implementation of Triple-Resonance Sequences Determination of Coupling Constants HMBC According to Keeler/Neuhaus E.COSY Type Experiments Measurement of Coupling Constants from Multiquantum Coherence 569 Acknowledgments 572 References Computer-Aided Analysis of Multidimensional NMR Spectra 581 Hans Robert Kalbitzer 4.1 Introduction Enhancement of Spectral Quality Time-Domain Fütering Time-Domain Manipulations for Ridge Suppression Frequency-Domain Filtering 586

7 xiv CONTENTS Base-Plane Correction in the Frequency Domain Removal of Spectral Artifacts Symmetry Enhancement Linear Prediction and Related Methods Maximum Entropy Reconstructions and Related Methods Peak and Multiplet Recognition PeakPicking Cluster Analysis Multiplet Recognition Recognition of Spin Systems and Sequential Assignment of Resonance Lines Identification of Spin Systems Chain Sequential Assignments Pattern Recognition in Multidimensional NMR Spectra Peak and Multiplet Integration Conclusions and Outlook 611 References NMR of Peptides 619 Horst Kessler and Stephan Seip 5.1 Introduction Assignment of Signals Various Techniques Efficient Assignment Strategies Assignment of Spin Systems Sequential Assignment Extraction of Conformationally Relevant Parameters NOE Effects NOE or ROE? Evaluation of NOESY and ROESY Spectra Determination of Coupling Constants The HMBC Experiment fc>,-filtered TOCSY (HETLOC) Further Techniques Structure Determination of Peptides Backbone Conformation Sidechain Conformation Relaxation Parameters and Molecular Dynamics 647 Acknowledgment 650 References 650

8 CONTENTS xv 6. Protein Structure Calculation Using NMR Restraints 655 H. Jane Dyson and Peter E. Wright 6.1 Introduction: Nature of the Problem Sequential Assignment: The Building Blocks Assignment of Spin Systems Sequential Connection of Spin Systems Distance Constraints from the NOE Obtaining Estimates of NOE Intensity from 2D and 3D Spectra Initial Slope Methods and the Isolated Spin-Pair Approximation Relaxation Matrix Approaches to Distance Evaluation Use of Distance Bounds Dihedral Angle Constraints from Coupling Constants Measurement of Backbone Dihedral Angles Estimation of Sidechain Dihedral Angles Methods for Use with Large Molecules Methods for Obtaining Stereospecific Assignments Other Constraints Hydrogen Bond Constraints Restriction of Conformational Space by Grid Searching Computational Methods Structure Calculation by Distance Geometry and Molecular Dynamics Refinement Alternative Approaches to Structure Calculation Back-Calculation and the NMR R-Factor Comparison of X-Ray and NMR Structure Determination Examples of Structures Determined by Both Methods Chain Mobility How Can It Be Detected? Conclusions The Future Potential for High-Resolution, High-Precision Structures by NMR: The Molecular Weight Limit 693 Acknowledgments 693 References 694

9 xvi CONTENTS 7. Studies of Nucleic Acid Structures Based on NMR Results 699 Igor Goljer and Philip H. Bolton 7.1 Introduction Sample Considerations Structural Features of Nucleic Acids Assignment Strategies Assignment of B-form Structures Assignment of A-Form Structures Nucleic Acids with syn Residues Homonuclear Scalar Couplings Heteronuclear Scalar Couplings NMR Studies of the Fine Structure and Dynamics of Duplex DNA Total Relaxation/Iterative Approach Restrained Molecular Dynamics Dynamical Structure of DNA Consideration of DNA Motion Inclusion of Coupling-Constant Data Methods of Evaluating the Agreement between Predicted and ObservedNOEs Can the Fine Structure of Duplex DNA Be Determined by NMR-based Methods? Qualitative Structure Determinations of Nucleic Acids Studies on Curved DNA: Comparison of Crystallography and NMR Results Studies of RNA-DNA Hybrids Summary 736 Acknowledgments 736 References Two-Dimensional and Related NMR Methods in Structural Analyses of Oligosaccharides and Polysaccharides 741 Janusz Dabrowski 8.1 Introduction Identification of the Component Sugar Residues in Oligosaccharides Establishing the Number of Constituent Sugar Residues Establishing the Types of Constituent Sugar Residues and Their Anomeric Configuration 757

10 CONTENTS xvii 8.3 Determination of Oligosaccharide Sequences and Interresidue Linkage Positions Heteronuclear 'H/ l3 C-Correlated Spectroscopy D Spectroscopy Concluding Remarks 779 Acknowledgment 780 References Steroid Structural Analysis by Two-Dimensional NMR 785 William R. Croasmun and Robert M. K. Carlson 9.1 Introduction Overview of 2D NMR Applications to Various Steroid Classes Primary Considerations in Sample-limited Steroid 2D NMR Studies Field Strength Solvent-induced Shifts Connectivity Diagrams for Use with Steroid 2D NMR Data NMR Parameters and 2D Methods for Steroids Chemical Shifts J-Couplings Dipolar Interactions Steroid Structure Determination Skeletal Structure and Assignment of 'H and l3 C Chemical Shifts Stereochemistry Conclusion 832 References Applications of Two-Dimensional NMR to the Characterization of Synthetic Organic Materials 841 Peter L. Rinaldi 10.1 Introduction Structure of Organometallic Complexes by COSY and NOESY Ligand Identification by COSY Complexation Stereochemistry from NOESY 844

11 xviii CONTENTS 10.3 Structure of Diels-Alder Products by Combined Application of COSY and Heteronuclear Shift Correlation Polymer Segment End-Structure Determination by Long-Range Correlation Experiments Polyisobutylene-b-Polybutadiene Diblock Polymer Polyisobutylene End-Group Strucutre by HMQC and HMBC { 2 H} I3 C Polarization Transfer NMR Reactivity of Poly(styrene/methylmethacrylate) Copolymer Special Requirements for Performing Triple-Resonance Experiments Structure Assignment of Large Molecules by 2D-Heteronuclear Spin-Locking (HSL) Studies Comparison of HOESY and HSL: Gramicidin-S Resonance Assignments Poly(p-/-butylstyrene) Resonance Assignments Using Heteronuclear Spin Locking Special Requirements for Performing Heteronuclear Spin-locking Experiments Conclusions 870 Acknowledgments 870 References Two-Dimensional NMR in Natural Products and Pharmaceutical Chemistry 873 Gary E. Martin and Ronald C. Crouch 11.1 Introduction Elucidation of the Structure of a Sesquiterpene Degradation Product of 1-Bromomaaliol Utilization of COSY Data Heteronuclear Chemical Shift Correlation Data HMQC-COSY and HMQC-TOCSY: An Alternative to COSY Elucidation of the Structure of the Novel Spiro Nonacyclic Alkaloid Cryptospirolepine The COSY Spectrum of Cryptospirolepine (3) 'H- 15 NHMQC Utilization of DEPT-HMQC and DEPT-HMQC-TOCSY to Simplify the Congested Spectra of the Cardenolide Digoxin 897

12 CONTENTS xix 11.5 New Directions Heteronuclear 2D NMR Using Micro Probes Micro Inverse Detection Preliminary Studies Using Cryptolepine Hydrochloride (5) as a Model Compound Application of Micro Inverse Detection to Larger Natural Products Digoxin (4) Conclusions 912 References 912 Glossary 915 Index 927