NMR-Based Quantum Mechanical Analysis Builds Trust and Orthogonality in Structural Analysis: The Case of a Bisdesmosidic Triglycoside as Withania somnifera Aerial Parts Marker

The present study demonstrates the relationship between conventional and quantum mechanical (QM) NMR spectroscopic analyses, shown here to assist in building a convincingly orthogonal platform for the solution and documentation of demanding structures. Kaempferol-3-O-robinoside-7-O-glucoside, a bisdesmosidic flavonol triglycoside and botanical marker for the aerial parts of Withania somnifera, served as an exemplary case. As demonstrated, QM-based ¹H iterative full spin analysis (HiFSA) advances the understanding of both individual nuclear resonance spin patterns and the entire ¹H NMR spectrum of a molecule and establishes structurally determinant, numerical HiFSA profiles. The combination of HiFSA with regular 1D ¹H NMR spectra allows for simplified yet specific identification tests via comparison of high-quality experimental with QM-calculated spectra. HiFSA accounts for all features encountered in ¹H NMR spectra: nonlinear high-order effects, complex multiplets, and their usually overlapped signals. As HiFSA replicates spectrum patterns from field-independent parameters with high accuracy, this methodology can be ported to low-field NMR instruments (40-100 MHz). With its reliance on experimental NMR evidence, the QM approach builds up confidence in structural characterization and potentially reduces identity analyses to simple 1D ¹H NMR experiments. This approach may lead to efficient implementation of conclusive identification tests in pharmacopeial and regulatory analyses: from simple organics to complex Natural Products.