## 2 Results and Discussion
### Fingerprinting of Cinnamon NMR Dataset
#### 2.4.2 Secondary Metabolites  
Investigation of the aromatic region (\(\delta_{\rm H}\) = 6.0-9.0 ppm) revealed characteristic signals for major secondary cinnamate metabolites, namely (\(Z\))- cinnamic acid (N7), (\(E\))-cinnamic acid (N8), (\(E\))-cinnamaldehyde (N9), cinnamaldehyde dimethyl acetal (N11) detected in nearly all samples except for CP-3, where cinnamates were totally absent, Figure 4. Identification of these secondary metabolites was on the basis of \({}^{1}\)H-NMR and 2D-NMR spectral data _viz_ COSY, HSQC, and HMBC (Table S2) and in accordance with those previously reported in _Cinnamomum_ sp. [44]. Two additional phenolics identified in this study in cinnamon extract included (\(E\))-methoxy cinnamaldehyde (N10), coumarin (N13), and protocatechuic acid (N12). (\(E\))-methoxy cinnamaldehyde (N10) was identified only in \(C\). _verum_ from its three-spin system similar to that of (\(E\))-cinnamaldehyde with an aldehyde doublet signal at \(\delta\) 9.62 (\(J\) = 7.8 Hz) together with major singlet signal at \(\delta\) 3.84 ppm assigned for the methoxy group. Additionally, coumarin (N13) was identified in the \({}^{1}\)H-NMR spectrum down-field region via the presence of four aromatic signals (Table S2). In detail, two characteristic threefold doublet signals at \(\delta\) 7.34 (\(J\) = 8.4, 7.8, 1.2 Hz) and 7.59 (\(J\) = 8.4, 6, 1.2 Hz) ppm were assigned for H-6 and H-7 of the benzenoid ring, respectively. Moreover, two doublets of doublets appeared at \(\delta\) 7.4 (\(J\) = 6, 1.8 Hz) and 7.63 (\(J\) = 7.8, 1.2 Hz) ppm corresponding to H-8 and H-5, respectively. The presence of hepatotoxic coumarin indicates low-grade cinnamon and poses NMR as a new tool for its detection in cinnamon drugs. The \({}^{1}\)H-NMR spectrum revealed the presence of phenolic acid with the AMX system with signals resonating at \(\delta\) 8.01 (dd, \(J\) = 8.4, 1.2 Hz), 6.78 (d, \(J\) = 8.4 Hz) and 7.42 (overlapped) ppm assigned for H-6, H-7, and H-2 of protocatechuic acid (N12), respectively. Assignments of aromatic metabolites were verified via 2D-NMR spectral data (Table S2). Among commercial samples, CP-3 showed the most distinct spectrum, Figure 4, assigned to three vitamins present in this preparation. Niacin or vitamin B3 (N14) was identified in the downfield region (\(\delta_{\rm H}\) 7.5 to 9.5 ppm), showing two downfield signals at \(\delta\) 9.02 (d, \(J\) = 1.8 Hz) and 8.69 (dd, \(J\) = 1.2, 4.8 Hz) ppm assigned for protons at \(\alpha\)- position (H-2 and H-6, respectively). Moreover, two other heteroaromatic protons resonating at \(\delta\) 8.28 (dt, \(J\) = 1.8, 7.8 Hz) and 7.54 (dd, \(J\) = 4.8, 7.8 Hz) ppm ascribed to H-4 and H-5, respectively. Coupling constants between H-4/H-5 and H-5/H-6 ortho coupling that there are two vicinal coupling constants of 7.8 and 4.8 Hz related to different \({}^{3}\)\({}_{HH}\) between pyridine protons and assigning it as 3-monosubstituted pyridine structure of niacin [45]. Among other vitamins detected in the up-field region (\(\delta_{\rm H}\) 0.5 to 5.5 ppm) of CP-3 commercial products are ascorbic acid/vitamin C (N15) and \(\alpha\)-tocopherol/vitamin E (N16). In detail, ascorbic acid (N15) was detected from doublet and triplet signals with \(J\) = 6 Hz at \(\delta\) 3.67 and 3.89 ppm, respectively, indicating (-CH-CH\({}_{2}\)-) deshiselded alkyl chain characteristic for ascorbic acid. The appearance of the singlet signal at \(\delta\) 4.78 of C-4 instead of doublet indicated the instability of vitamin C and the presence of its oxidative product in CP-3. The presence of such degradation product may be due to the presence of metal ionssuch as manganese and chromium in CP-3 product which act as a catalyst, or may be due to storage conditions [46]. Additionally, _a_-tocopherol (N16) exhibited three singlets signals at \(\delta\) 1.95, 1.98, and 2.07 ppm assigned to three desshielded methyl groups attached to the aromatic ring.