Based on a brief revision of what constitutes state-of-the-art "quantitative experimental conditions" for (1)H quantitative NMR (qHNMR), this comprehensive review contains almost 200 references and covers the literature since 1982 with emphasis on natural products. It provides an overview of the background and applications of qHNMR in natural products research, new methods such as decoupling and hyphenation, and analytical potential and limitations, and compiles information on reference materials used for and studied by qHNMR. The dual status of natural products, being single chemical entities and valuable biologically active agents that need to be purified from complex matrixes, results in an increased analytical demand when testing their deviation from the singleton composition ideal. The outcome and versatility of reported applications lead to the conclusion that qHNMR is currently the principal analytical method to meet this demand. Considering both 1D and 2D (1)H NMR experiments, qHNMR has proved to be highly suitable for the simultaneous selective recognition and quantitative determination of metabolites in complex biological matrixes. This is manifested by the prior publication of over 80 reports on applications involving the quantitation of single natural products in plant extracts, dietary materials, and materials representing different metabolic stages of (micro)organisms. In summary, qHNMR has great potential as an analytical tool in both the discovery of new bioactive natural products and the field of metabolome analysis.

In any biomedical and chemical context, a truthful description of chemical constitution requires coverage of both structure and purity. This qualification affects all drug molecules, regardless of development stage (early discovery to approved drug) and source (natural product or synthetic). Purity assessment is particularly critical in discovery programs and whenever chemistry is linked with biological and/or therapeutic outcome. Compared with chromatography and elemental analysis, quantitative NMR (qNMR) uses nearly universal detection and provides a versatile and orthogonal means of purity evaluation. Absolute qNMR with flexible calibration captures analytes that frequently escape detection (water, sorbents). Widely accepted structural NMR workflows require minimal or no adjustments to become practical 1H qNMR (qHNMR) procedures with simultaneous qualitative and (absolute) quantitative capability. This study reviews underlying concepts, provides a framework for standard qHNMR purity assays, and shows how adequate accuracy and precision are achieved for the intended use of the material.

Covering the literature from mid-2004 until the end of 2011, this review continues a previous literature overview on quantitative 1 H NMR (qHNMR) methodology and its applications in the analysis of natural products. Among the foremost advantages of qHNMR is its accurate function with external calibration, the lack of any requirement for identical reference materials, a high precision and accuracy when properly validated, and an ability to quantitate multiple analytes simultaneously. As a result of the inclusion of over 170 new references, this updated review summarizes a wealth of detailed experiential evidence and newly developed methodology that supports qHNMR as a valuable and unbiased analytical tool for natural product and other areas of research.

Quantitative 1 H NMR (qHNMR) provides a value-added dimension to the standard spectroscopic data set involved in structure analysis, especially when analyzing bioactive molecules and elucidating new natural products. The qHNMR method can be integrated into any routine qualitative workflow without much additional effort by simply establishing quantitative conditions for the standard solution 1 H NMR experiments. Moreover, examination of different chemical lots of taxol and a Taxus brevifolia extract as working examples led to a blueprint for a generic approach to performing a routinely practiced 13 C-decoupled qHNMR experiment, and for recognizing its potential and main limitations. The proposed protocol is based on a newly assembled 13 C GARP broadband decoupled proton acquisition sequence that reduces spectroscopic complexity by removal of carbon satellites. The method is capable of providing qualitative and quantitative NMR data simultaneously and covers various analytes from pure compounds to complex mixtures such as metabolomes. Due to a routinely achievable dynamic range of 300:1 (0.3%) or better, qHNMR qualifies for applications ranging from reference standards to biologically active compounds to metabolome analysis. Providing a "cookbook" approach to qHNMR, acquisition conditions are described that can be adapted for contemporary NMR spectrometers of all major manufacturers. The world's pool of natural products plays an important role as an (in)exhaustible resource for evolutionary-shaped molecules. Natural products are valuable research tools, which in part is due to their biological potency (see comprehensive reviews [1][2][3][4] ). When natural products are used as biomedical agents, and in consistency with the pharmacophore model, it is the combination of their specific chemical structure and/or reactivity that forms their relationship with a biological target and ultimately defines their essential structural features. Consequently, chemical constitution plays a key role in biological activity, and, therefore, all structure related information obtainable from a biologically active agent is by default relevant. Ultimately, any variation of structural parameters has the potential to introduce variations in biological activity. This relationship holds regardless of the magnitude of the biological perturbation, i.e., whether there is slight or a substantial change in potency, or even an alteration in the type of biological response. The well-documented subtleties of mammalian hormonal steroids can serve as a distinguished example in this regard.⊥ Dedicated to Dr. Norman R. Farnsworth on the occasion of his 77 th birthday.* To whom correspondence should be addressed. Tel (312) 355-1949355- . Fax (312)-355-2693. gfp@uic.edu. Supporting Information Available.This material is available free of charge via the Internet at http://pubs.acs.org. Further information on qNMR methodology, instrument parameter files for the NMR major manufacturer's spectrometers, and original FIDs of the taxol qHNMR experime...

ClpC1 is an emerging new target for the treatment of Mycobacterium tuberculosis infections, and several cyclic peptides (ecumicin, cyclomarin A, and lassomycin) are known to act on this target. This study identified another group of peptides, the rufomycins (RUFs), as bactericidal to M. tuberculosis through the inhibition of ClpC1 and subsequent modulation of protein degradation of intracellular proteins. Rufomycin I (RUFI) was found to be a potent and selective lead compound for both M. tuberculosis (MIC, 0.02 μM) and Mycobacterium abscessus (MIC, 0.4 μM). Spontaneously generated mutants resistant to RUFI involved seven unique single nucleotide polymorphism (SNP) mutations at three distinct codons within the N-terminal domain of clpC1 (V13, H77, and F80). RUFI also significantly decreased the proteolytic capabilities of the ClpC1/P1/P2 complex to degrade casein, while having no significant effect on the ATPase activity of ClpC1. This represents a marked difference from ecumicin, which inhibits ClpC1 proteolysis but stimulates the ATPase activity, thereby providing evidence that although these peptides share ClpC1 as a macromolecular target, their downstream effects are distinct, likely due to differences in binding.

Botanical dietary supplements and herbal remedies are widely used for health promotion and disease prevention. Due to the high chemical complexity of these natural products, it is essential to develop new analytical strategies to guarantee their quality and consistency. In particular, the precise characterization of multiple botanical markers remains a challenge. This study demonstrates how a combination of computer-aided spectral analysis and 1D quantitative 1H NMR spectroscopy (qHNMR) generates the analytical foundation for innovative means of simultaneously identifying and quantifying botanical markers in complex mixtures. First, comprehensive 1H NMR profiles (fingerprints) of selected botanical markers were generated via 1H iterative Full Spin Analysis (HiFSA) with PERCH. Next, the 1H fingerprints were used to assign specific 1H resonances in the NMR spectra of reference materials, enriched fractions and crude extracts of Ginkgo biloba leaves. These 1H fingerprints were then used to verify the assignments by 2D NMR. Subsequently, a complete purity and composition assessment by means of 1D qHNMR was conducted. As its major strengths, this tandem approach enables the simultaneous quantification of multiple constituents without the need for identical reference materials, the semi-quantitative determination of particular sub-classes of components, and the detection of impurities and adulterants.

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. Spectral simulations paired with iteration are shown to be essential tools for complete spectral interpretation, adequate precision, and unambiguous HNMR-driven dereplication and metabolomic analysis. The broader applicability of the recommendation relates to the physicochemical properties of hydrogen (1H) and its ubiquity in organic molecules, making HNMR spectra an integral component of structure elucidation and verification. Regardless of origin or molecular weight, the HNMR spectrum of a compound can be very complex and encode a wealth of structural information that is often obscured by limited spectral dispersion and the occurrence of higher order effects. This altogether limits spectral interpretation, confines decoding of the underlying spin parameters, and explains the major challenge associated with the translation of HNMR spectra into tabulated information. On the other hand, the reproducibility of the spectral data set of any (new) chemical entity is essential for its structure elucidation and subsequent dereplication. Handling and documenting HNMR data with adequate precision is critical for establishing unequivocal links between chemical structure, analytical data, metabolomes, and biological activity. Using the full potential of HNMR spectra will facilitate the general reproducibility for future studies of bioactive chemicals, especially of compounds obtained from the diversity of terrestrial and marine organisms.

A novel extracellular metabolite with an unprecedented diterpenoid skeleton, 8-[(5-carboxy-2-hydroxy)benzyl]-2-hydroxy-1,1,4a,7, 8-pentamethyl-1,2,3,4,4a,6,7,8,8a,9,10,10a-dodecahydrophenanthrene , has been isolated from the culture medium of the terrestrial cyanobacterium Nostoc commune Vaucher (EAWAG 122b) by means of bioguided isolation. The molecule was designated as noscomin. The structure was determined by spectroscopic methods, mainly NMR and mass spectrometry. Noscomin exhibited antibacterial activity against Bacillus cereus, Staphylococcus epidermidis, and Escherichia coli.