Nmr

# Publications/

Hyphenating Centrifugal Partition Chromatography with Nuclear Magnetic Resonance through Automated Solid Phase Extraction

Journal: Analytical Chemistry (RoMEO status: White) Published on
Categories: publications
Subjects: Analytical Chemistry Preparative chemistry Reverse engineering Hyphenation CPC NMR SPE

Centrifugal partition chromatography (CPC) and all countercurrent separation apparatus provide chemists with efficient ways to work with complex matrixes, especially in the domain of natural products. However, despite the great advances provided by these techniques, more efficient ways of analyzing the output flow would bring further enhancement. This study describe a hyphenated approach made by coupling NMR with CPC through a hybrid-indirect coupling made possible by using a solid phase extraction (SPE) apparatus intended for high-pressure liquid chromatography (HPLC)-NMR hyphenation.

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# Publications/

Dissemination of Original NMR Data Enhances Reproducibility and Integrity in Chemical Research

Journal: Natural Product Reports (RoMEO status: Yellow) Published on
Categories: publications
Subjects: Fundamental research NMR raw data

The notion of data transparency is gaining a strong awareness among the scientific community. The availability of raw data is actually regarded as a fundamental way to advance science by promoting both integrity and reproducibility of research outcomes. Particularly, in the field of natural product and chemical research, NMR spectroscopy is a fundamental tool for structural elucidation and quantification (qNMR). As such, the accessibility of original NMR data, i.e., Free Induction Decays (FIDs), fosters transparency in chemical research and optimizes both peer review and reproducibility of reports by offering the fundamental tools to perform efficient structural verification.

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# Publications/

OpenAccess Toward Structural Correctness: Aquatolide and the Importance of 1D Proton NMR FID Archiving

Journal: Journal of Organic Chemistry (RoMEO status: White) Published on
Categories: publications
Subjects: Pharmacognosy Phytochemistry NMR FID raw data Spin simulation

The revision of the structure of the sesquiterpene aquatolide from a bicyclo[2.2.0]hexane to a bicyclo[2.1.1]hexane structure using compelling NMR data, X-ray crystallography, and the recent confirmation via full synthesis exemplify that the achievement of “structural correctness” depends on the completeness of the experimental evidence. Archived FIDs and newly acquired aquatolide spectra demonstrate that archiving and rigorous interpretation of 1D 1H NMR data may enhance the reproducibility of (bio)chemical research and curb the growing trend of structural misassignments.

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# Publications/

Bioadhesive properties of enriched proanthocyanidins primers

Journal: Dental Materials (RoMEO status: Green) Published on
Categories: publications
Subjects: Pharmacognosy Phytochemistry Dentistry OPAC NMR

Plant derived proanthocyanidins are well-established compounds exhibiting high dentin biomodification potency. Among the effects, enhanced tissue biomechanics and biostability are of relevance to restorative dentistry. This study evaluated the adhesive properties of an enriched proanthocyanidin primer on the bond strength of experimental resin-based adhesives containing variable concentrations of HEMA.

# Publications/

Subtle Chemical Shifts Explain the NMR Fingerprints of Oligomeric Proanthocyanidins with High Dentin Biomodification Potency

Journal: Journal of Organic Chemistry (RoMEO status: White) Published on
Categories: publications
Subjects: Pharmacognosy Phytochemistry Dentistry OPAC NMR

The ability of certain oligomeric proanthocyanidins (OPACs) to enhance the biomechanical properties of dentin involves collagen cross-linking of the 1.3–4.5 nm wide space via protein–polyphenol interactions. A systematic interdisciplinary search for the bioactive principles of pine bark has yielded the trimeric PAC, ent-epicatechin-(4β→8)-epicatechin-(2β→O→7,4β→8)-catechin (3), representing the hitherto most potent single chemical entity capable of enhancing dentin stiffness. Building the case from two congeneric PAC dimers, a detailed structural analysis decoded the stereochemistry, spatial arrangement, and chemical properties of three dentin biomodifiers.

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# Posters/

Chemical nano shifts explain the NMR fingerprints of dentin-enhancing oligomeric proanthocyanidins

1D NMR spectra contain a wealth of vital structural information that can enhance the description of bioactive molecules. The present study demonstrates how quantum-mechanics driven 1H iterative Full Spin Analysis (QM-HiFSA) is capable of distinguishing spectral detail that cannot be interpreted manually or visually, but provides important information of the 3D structure and bonding (re-)activity of the molecules. This approach is established by analyzing 1D NMR spectra of oligomeric proanthocyanidins (OPACs), which exhibit high dentin bioactivity, and were isolated from the inner bark of pine.

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# Posters/

Dissemination of original NMR data enhances the reproducibility of natural product research

The acquisition of 1D 1H NMR (HNMR) spectra is one of earliest steps in characterizing natural products and other organic molecules. For publication, HNMR information usually is “converted” into a table format, and sometimes spectral plots are provided. However, this transformation is lossy and frequently insufficient for unambiguous dereplication. This ambiguity can even lead to structural revision, such as in the recent case of aquatolide (1), a sesquiterpene lactone from Asteriscus aquaticus.

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# Posters/

K-targeted isolation of C-glycosylflavones from Vitex agnus-castus by countercurrent methodology

C-glycosylated flavones, including orientin, isoorientin, vitexin, and isovitexin, are minor but biologically significant constituents of fruit extracts of the chaste-tree (Vitex agnus-castus L.), a botanical supplement used to treat PMS and postmenopausal symptoms. The partition coefficient, or K-value, is the ratio of the concentration of a compound in each phase of a biphasic solvent mixture and is a physicochemical property of a particular compound in a particular solvent system. This value can be used to predict retention volume (V ret) in a countercurrent separation procedure.

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# Publications/

Mimicking the Hierarchical Functions of Dentin Collagen Cross-Links with Plant Derived Phenols and Phenolic Acids

Journal: Langmuir (RoMEO status: White) Published on
Categories: publications
Subjects: Pharmacognosy Phytochemistry Dentistry Polyphenols NMR

Proanthocyanidins (PACs) are secondary plant metabolites that mediate nonenzymatic collagen cross-linking and enhance the properties of collagen based tissue, such as dentin. The extent and nature of cross-linking is influenced by the composition and specific chemical structure of the bioactive compounds present in certain PAC-rich extracts. This study investigated the effect of the molecular weight and stereochemistry of polyphenol compounds on two important properties of dentin, biomechanics, and biostability. For that, purified phenols, a phenolic acid, and some of its derivatives were selected: PAC dimers (A1, A2, B1, and B2) and a trimer (C1), gallic acid (Ga), its esters methyl-gallate (MGa) and propyl-gallate (PGa), and a pentagalloyl ester of glucose (PGG).

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# Publications/

OpenAccess Essential Parameters for Structural Analysis and Dereplication by 1H NMR Spectroscopy

Journal: Journal of Natural Products (RoMEO status: White) Published on
Categories: publications
Subjects: Pharmacognosy Phytochemistry NMR Spin simulation

The present study demonstrates the importance of adequate precision when reporting the δ and J parameters of frequency domain 1H NMR (HNMR) data. Using a variety of structural classes (terpenoids, phenolics, alkaloids) from different taxa (plants, cyanobacteria), this study develops rationales that explain the importance of enhanced precision in NMR spectroscopic analysis and rationalizes the need for reporting Δδ and ΔJ values at the 0.1–1 ppb and 10 mHz level, respectively.

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# Publications/

Comparative Analyses of Stilbenoids in Canes of Major Vitis vinifera L. Cultivars

Grapevine canes are rich in resveratrol and its complex derivatives. These compounds have many biological activities and are needed mainly for health purposes. Canes, which are often wasted, can be used to produce these high-value compounds at low cost. We studied sixteen Vitis vinifera L. cultivars among the most widely cultivated ones worldwide. Polyphenols were extracted from their canes and identified by liquid chromatography–nuclear magnetic resonance spectroscopy. We accurately determined the content of E-ε-viniferin, E-resveratrol, E-piceatannol, and vitisin B and, for the first time, that of hopeaphenol and miyabenol C.

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# Publications/

Stilbenoid Profiles of Canes from Vitis and Muscadinia Species

We present stilbenoid profiles of canes from 16 grapevines. Fifteen stilbenoids were obtained through isolation and structure identification using MS, NMR, and [α]D or as commercial standards. An HPLC–UV method for the simultaneous quantification of nine of these stilbenoids was developed and applied to canes of Vitis amurensis, Vitis arizonica, Vitis berlandieri, Vitis betulifolia, Vitis cinerea, Vitis × champini, Vitis × doaniana, Vitis labrusca, Vitis candicans (syn. Vitis mustangensis), Vitis riparia, Vitis rupestris, Vitis vinifera, Muscadinia rotundifolia, and a V.

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# Conferences/

Hyphenating countercurrent chromatography with NMR and mass spectrometry. How to enhance the range of the liquid phases

Countercurrent chromatography techniques are increasingly used in the fractionation and purification steps of natural products due to their excellent versatility and efficiency. However, one of the major bottlenecks in liquid-liquid chromatography is the solvent system selection. In this work, a NMR-based analysis of complex solvent mixtures was developed for biphasic system selection and modification. This allowed us to develop more versatile separation conditions, such as gradients. Additionally, we hyphenated our countercurrent chromatography device with NMR and mass spectrometry.

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