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NMR Characterization of Natural and Synthetic Anthocyanidins: Establishing a Foundation for Designing Functional O-Methylated Analogs
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DOI：10.1177/1934578X261444910.png)
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Abstract
En 中文
ObjectiveAs methylation affects the biological activities of secondary metabolites, novel methylated anthocyanins hold potential as new functional materials. While accurate structural determination is essential for the development of these novel derivatives, discrepancies in the nuclear magnetic resonance (NMR) assignments of anthocyanidins are observed in the literature. This study aims to achieve accurate NMR signal assignments for major natural anthocyanidins and a non-natural analog, then systematically elucidate the effects of O-methylation to establish reliable foundational data for future structural elucidation.MethodsFive natural anthocyanidins (cyanidin, peonidin, delphinidin, petunidin, and malvidin) were isolated and purified from bilberry (Vaccinium myrtillus L.) extract following acid hydrolysis. Additionally, a non-natural analog, 3,7,3 ',4 '-tetra-O-methylcyanidin, was synthesized from quercetin. Comprehensive structural analysis of these compounds was conducted using 1H-, 13C- and two-dimensional NMR spectroscopy.ResultsSignal assignments were achieved for all compounds, and previous literature discrepancies regarding the H-6 and H-8 signals were resolved. In 1H-NMR, O-methylation generally induced downfield shifts for aromatic protons on the substituted rings. In 13C-NMR, ipso and para carbons typically exhibited downfield shifts, whereas ortho methine carbons shifted upfield. While 3,7,3 ',4 '-tetra-O-methylcyanidin exhibited trends similar to natural anthocyanidins, O-methylation on the A- and C-rings demonstrated slightly different shift changes.ConclusionIn this study, we systematically summarized the fundamental trends of 1H- and 13C-NMR chemical shifts for anthocyanidins. Furthermore, effects on the spectra due to O-methylation of hydroxyl groups including those on the A- and C-rings were confirmed. These findings provide an essential spectroscopic basis for identifying novel O-methylated anthocyanidins.
Keywords:
NMR
anthocyanin
O-methylcyanidin
O-methylation
Vaccinium myrtillus L.
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IF:
1.4
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188
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7.8K
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