Exploring pyrrolizidine alkaloids in Crotalaria paulina: Isolation and identification of a promising compound

Baia, V.; Oliveira, Ramon P.; Alvarenga, Elson S.; Pinto, Bryan Nickson Santana; Demuner, Antônio J.

doi:10.1016/j.molstruc.2023.136171

Cited by 2 publications

(2 citation statements)

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“…In this context, 1 H nuclear magnetic resonance (NMR) spectroscopy, 13 C NMR, and high-resolution mass spectrometry are central spectrometric techniques for structural elucidation. [23][24][25] Despite the diversity of existing techniques, it is not uncommon to find in the literature molecules that have had their structures incorrectly assigned. 26,27 Recently, Sarotti reported the structural revision of the unusual diterpenes, curcusones I and J (9a and 9b, Figure 3), using DFT calculations and NMR coupling constant approaches.…”

Section: Introductionmentioning

confidence: 99%

“…29 A strategy that has gained prominence recently is the use of calculations based on quantum mechanics to simulate 1 H and 13 C NMR spectra. 24,25,[30][31][32] This is also driven by the growing computational power and user-friendly graphical interface software, that does not require expertise in programming languages. 33,34 Distinctive approaches can be used to calculate shielding tensors.…”

Section: Introductionmentioning

confidence: 99%

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Deciphering molecular structures: NMR spectroscopy and quantum mechanical insights of halogenated 4H‐Chromenediones

Martins,

Souto,

Hoye

et al. 2024

Magnetic Reson in Chemistry

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Sesquiterpene lactones (SL) represent a class of secondary metabolites found in the Asteraceae family, notable for their unique structures. The SL α‐santonin (1) and its derivatives are worthy of mention due to their diverse biological properties. Additionally, 4H‐chromenes and 4H‐chromones are appealing frameworks holding the capability to be used as structural motifs for new drugs. Furthermore, unambiguous structural elucidation is crucial for developing novel compounds for diverse applications. In this context, it is common to find in the literature molecules erroneously assigned. Therefore, the use of quantum mechanical calculations to simulate NMR chemical shifts has emerged as a valuable strategy. In this work, we conceived the synthesis of two halogenated 4H‐chromenediones derived from photosantonic acid (2), a photoproduct arising from irradiation of α‐santonin (1) in the ultraviolet region. The structure of the chlorinated and brominated products was determined by NMR analysis, with the aid of quantum mechanical calculations at the B3LYP/6‐311 + G(2d,p)//M062x/6‐31 + G(d,p) level of theory. All analyses were in agreement and led to the assignment of the brominated 4H‐chromene‐2,7‐dione as (3S,3aS,5aR,9bS)‐5a‐(2‐bromopropan‐2‐yl)‐3‐methyl‐3,3a,5,5a,8,9b‐hexahydro‐4H‐furo[2,3‐f]chromene‐2,7‐dione (11b) and of the chlorinated 4H‐chromene‐2,7‐dione as (3S,3aS,5aR,9bS)‐5a‐(2‐chloropropan‐2‐yl)‐3‐methyl‐3,3a,5,5a,8,9b‐hexahydro‐4H‐furo[2,3‐f]chromene‐2,7‐dione (12b). The diastereoselectivities of the reactions were explained based on products and intermediates formation energy calculated using B3LYP/6‐31 + G(d,p) as the level of theory. Structures 11b and 12b were identified as the thermodynamic and kinetic products of the reaction among all candidates. Consequently, the strategy utilized in this study is robust and successfully illustrates the use of quantum mechanical calculations in the structural elucidation of new compounds with potential applications as novel drugs or products.

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