Analytical Method Development: Structural Elucidation by NMR – V 2.0

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Analytical Method Development: Structural Elucidation by NMR – V 2.0

Standard Operating Procedure for Structural Elucidation by NMR in Analytical Method Development


Department Analytical Method Development
SOP No. SOP/AMD/114/2025
Supersedes SOP/AMD/114/2022
Page No. Page 1 of 14
Issue Date 19/05/2025
Effective Date 20/05/2025
Review Date 19/05/2026

1. Purpose

This SOP outlines the step-by-step methodology for using Nuclear Magnetic Resonance (NMR) spectroscopy to elucidate chemical structures, particularly for unknown impurities, degradants, and novel drug candidates in Analytical Method Development (AMD).

2. Scope

This SOP applies to all activities involving structural characterization by NMR for pharmaceutical substances, intermediates, and degradation products in the AMD laboratory, using 1H, 13C, DEPT, COSY, HSQC, HMBC, and NOESY techniques.

3. Responsibilities

  • NMR Analyst: Conducts acquisition and interpretation of 1D and 2D spectra.
  • Structure Elucidation Chemist: Proposes and confirms molecular structures.
  • QA Officer: Ensures proper documentation and data compliance.
  • Head – AMD: Reviews and approves finalized reports and structure proposals.

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4. Accountability

The Head of Analytical Method Development is accountable for ensuring structural elucidation by NMR is executed accurately, interpreted scientifically, and documented as per regulatory guidelines.

5. Procedure

5.1 Sample Preparation

  1. Weigh 5–15 mg of test material and dissolve in 0.6 mL of suitable deuterated solvent (DMSO-d6, CDCl3, CD3OD, etc.).
  2. Ensure solution is clear and fully dissolved. Filter if particulate matter is present.
  3. Label sample ID, solvent used, and analyst name on NMR tube.
  4. Document in Annexure-1: NMR Sample Log.

5.2 Acquisition of 1D Spectra

  1. Acquire 1H and 13C NMR spectra using default parameters:
    • Pulse sequence: zg30 (1H), zgpg30 (13C)
    • Scans: 16–128 (1H), 512–2k (13C)
  2. Apply manual phase and baseline correction.
  3. Assign solvent peak for reference.
  4. Log spectral settings in Annexure-2: Acquisition Parameters Sheet.

5.3 Acquisition of 2D Spectra

  1. Acquire the following based on analytical need:
    • COSY: To identify scalar (through-bond) proton-proton coupling
    • HSQC: To correlate 1H–13C directly bonded pairs
    • HMBC: For long-range heteronuclear correlations
    • NOESY: For spatial relationships in stereochemistry
  2. Use 256–1024 increments and minimum 8–16 scans per increment.
  3. Save and process using licensed software (e.g., TopSpin, MestReNova).
  4. Record parameters in Annexure-3: 2D NMR Acquisition Log.
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5.4 Structural Interpretation

  1. Begin with 1H and 13C assignment:
    • Use chemical shift, multiplicity, J-values, and integration
    • Identify exchangeable protons (OH, NH)
  2. Overlay 2D spectra to map correlations.
  3. Establish substructures and connect fragments via HMBC/COSY paths.
  4. Match spectral data to known reference compounds or propose new structure using fragmentation logic.
  5. Draw structure with atom numbers matching shift table.
  6. Log all findings in Annexure-4: Structure Elucidation Summary.

5.5 Reporting

  1. Prepare a comprehensive report including:
    • All spectral printouts (1D and 2D)
    • Chemical shift table with atom numbering
    • Annotated structure
    • Discussion of spectral interpretation
  2. Include comparison to known standards if available.
  3. Submit report for QA and final review by AMD head.

6. Abbreviations

  • NMR: Nuclear Magnetic Resonance
  • COSY: Correlated Spectroscopy
  • HSQC: Heteronuclear Single Quantum Coherence
  • HMBC: Heteronuclear Multiple Bond Correlation
  • NOESY: Nuclear Overhauser Effect Spectroscopy
  • DEPT: Distortionless Enhancement by Polarization Transfer

7. Documents

  1. NMR Sample Log – Annexure-1
  2. Acquisition Parameters Sheet – Annexure-2
  3. 2D NMR Acquisition Log – Annexure-3
  4. Structure Elucidation Summary – Annexure-4
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8. References

  • ICH Q3A(R2) – Impurities in New Drug Substances
  • USP <761> – NMR Spectroscopy
  • Spectroscopic Identification of Organic Compounds (Silverstein)

9. SOP Version

Version: 2.0

10. Approval Section

Prepared By Checked By Approved By
Signature
Date
Name
Designation
Department

11. Annexures

Annexure-1: NMR Sample Log

Sample ID Solvent Concentration Prepared By Date
IMP-NMR-114 DMSO-d6 10 mg/mL Sunita Reddy 18/05/2025

Annexure-2: Acquisition Parameters Sheet

Experiment Scans Pulse Program Spectral Width Temperature
1H 32 zg30 12 ppm 298 K
13C 1024 zgpg30 240 ppm 298 K

Annexure-3: 2D NMR Acquisition Log

Technique Scan Count Increments Comments
COSY 8 512 Clear coupling between aromatic protons
HSQC 16 1024 Matched proton-carbon pairs

Annexure-4: Structure Elucidation Summary

The unknown impurity was identified as a hydroxylated derivative of API-X. Spectral interpretation supported substitution on position C-6 via long-range correlations and confirmed with mass and IR data.

Revision History:

Revision Date Revision No. Details Reason Approved By
04/05/2025 2.0 Inclusion of full 2D NMR workflow for impurity ID Annual Review
Analytical Method Development V 2.0 Tags:, , , , , , , , , , , , , , , , , , , , , , , , , , , , ,