The quercetin dioxygenases (QDOs) are unusual metalloenzymes in that they display ring-opening dioxygenase activity with several different first-row transition metal ions which do not undergo redox changes during turnover. The QDOs are also unique in that the substrate binds as an η1-flavonolate rather than the η2 -bidentate mode seen in all reported model complexes. The flavonol substrates were early examples of excited state intramolecular proton transfer (ESIPT) phenomena, in which photoexcitation causes an H-atom exchange between the adjacent hydroxyl and ketone, generating an oxidopyrylium emissive state. These oxidopyryliums undergo ring-opening dioxygenations analogous to the enzymatic reactions. Our hypothesis is that lability of the divalent metal ion may allow access to a reactive oxidopyrylium intermediate via coordination switching from the oxy to ketone position, which allows reaction with O2. In this report, we use a straight-forward methylation strategy to generate a panel of flavonol and thioflavonol derivatives modeling several η1- and η2-coordination modes. Methylation of 3-hydroxythioflavone generates an air stable η1 hydroxopyrylium salt, which undergoes rapid ring-opening dioxygenation by deprotonation or photoexcitation. By comparison, the η1-methoxyflavonol does not react with O2 under any condition. We find that any of the studied flavonol derivatives, η1 or η2, which demonstrates ESIPT-like oxidopyrylium emissions undergo QDO-like ring-opening reactions with dioxygen. The implications of these results concerning the mechanism of QDOs and related dioxygenases is discussed.

The current study examined the phylogenetic pattern of medicinal species of the family Apiaceae based on flavonoid groups production, as well as the overall mechanism of the key genes involved in flavonol and flavone production. Thirteen species of the family Apiaceae were used, including Eryngium campestre from the subfamily Saniculoideae, as well as Cuminum cyminum, Carum carvi, Coriandrum sativum, Apium graveolens, Petroselinum crispum, Pimpinella anisum, Anethum graveolens, Foeniculum vulgare, Daucus carota, Ammi majus, Torilis arvensis, and Deverra tortuosa from the subfamily Apioideae. The seeds were cultivated, and the leaves were collected to estimate flavonoids and their groups, physiological factors, transcription levels of flavonol and flavone production-related genes. The phylogenetic relationship between the studied species was established using the L-ribosomal 16 (rpl16) chloroplast gene. The results revealed that the studied species were divided into two patterns: six plant species, E. campestre, C. carvi, C. sativum, P. anisum, An. graveolens, and D. carota, contained low content of flavonoids, while the other seven species had high content. This pattern of flavonoids production coincided with the phylogenetic relationships between the studied species. In contrast, the phylogeny of the flavonol and flavone synthase genes was incompatible with the quantitative production of their products. The study concluded that the increment in the production of flavonol depends on the high expression of chalcone synthase, chalcone isomerase, flavanone 3 hydroxylase, flavonol synthase, the increase of Abscisic acid, sucrose, and phenyl ammonia lyase, while flavone mainly depends on evolution and on the high expression of the flavone synthase gene.

The present study demonstrates the relationship between conventional and quantum mechanical (QM) NMR spectroscopic analyses, shown here to assist in building a convincingly orthogonal platform for the solution and documentation of demanding structures. Kaempferol-3-O-robinoside-7-O-glucoside, a bisdesmosidic flavonol triglycoside and botanical marker for the aerial parts of Withania somnifera, served as an exemplary case. As demonstrated, QM-based 1H iterative full spin analysis (HiFSA) advances the understanding of both individual nuclear resonance spin patterns and the entire 1H NMR spectrum of a molecule and establishes structurally determinant, numerical HiFSA profiles. The combination of HiFSA with regular 1D 1H NMR spectra allows for simplified yet specific identification tests via comparison of high-quality experimental with QM-calculated spectra. HiFSA accounts for all features encountered in 1H NMR spectra: nonlinear high-order effects, complex multiplets, and their usually overlapped signals. As HiFSA replicates spectrum patterns from field-independent parameters with high accuracy, this methodology can be ported to low-field NMR instruments (40-100 MHz). With its reliance on experimental NMR evidence, the QM approach builds up confidence in structural characterization and potentially reduces identity analyses to simple 1D 1H NMR experiments. This approach may lead to efficient implementation of conclusive identification tests in pharmacopeial and regulatory analyses: from simple organics to complex natural products.

A new method based on nano-liquid chromatography coupled to time-of-flight mass spectrometry (nano-LC-TOF-MS) using lock-mass calibration was developed to facilitate the accurate and routine characterization and quantification of phenolic compounds. Thus, it was applied to study cranberry syrups, in which, using negative ionization mode, a total of nine phenolic compounds were unequivocally identified using standards and 38 tentatively taking into account their retention time, accurate mass (errors<5 ppm) data and isotope pattern, as well as literature. Among them, 13 compounds, belonging to flavonols and iridoids conjugated with phenolic acids, were reported for first time in cranberry or cranberry based-products. The analytical method was also validated using chlorogenic acid, p-coumaric acid, (+)-catechin, (-)-epicatechin, procyanidin A2, quercetin 3-O-glucoside, quercetin 3-O-rhamnoside, quercetin, and myricetin standards. In this way, the analytical method showed adequate linearity, with R(2) above 0.99, and acceptable values of intra- and inter-day repeatability of the retention time and peak area. The detection limits and quantification were between 1.0-15.6 ng mL(-1) and 2.0-62.5 ng mL(-1), respectively. The method can be extended to characterize phenolic compounds in other food and plant matrices, and as well biological samples.

BACKGROUND: Because of their antioxidant and antimutagenic properties, flavonoids may reduce cancer risk. Some flavonoids have antiestrogenic effects that can inhibit the growth and proliferation of endometrial cancer cells.
METHODS: In order to examine the relation between dietary flavonoids and endometrial cancer, we analysed data from an Italian case-control study including 454 incident, histologically confirmed endometrial cancers and 908 hospital-based controls. Information was collected through a validated food-frequency questionnaire. We applied data on food and beverage composition to estimate the intake of flavanols, flavanones, flavonols, anthocyanidins, flavones, isoflavones, and proanthocyanidins. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated from multiple logistic regression models conditioned on age and study centre and adjusted for major confounding factors.
RESULTS: Women in the highest quartile category of proanthocyanidins with ≥3 mers vs the first three quartile categories had an OR for endometrial cancer of 0.66 (95% CI=0.48-0.89). For no other class of flavonoids, a significant overall association was found. There was a suggestion of an inverse association for flavanones and isoflavones among women with body mass index <25 kg m(-2), and, for flavanones, among parous or non-users of hormone-replacement therapy women.
CONCLUSIONS: High consumption of selected proanthocyanidins may reduce endometrial cancer risk.

Diets rich in flavonoids may reduce the risk of developing colorectal cancer. Flavonoids are widely distributed in foods of plant origin, though in the UK tea is the main dietary source. Our objective was to evaluate any independent associations of total dietary and non-tea intake of four flavonoid subclasses and the risk of developing colorectal cancer in a tea-drinking population with a high colorectal cancer incidence. A population-based case-control study (264 cases with histologically confirmed incident colorectal cancer and 408 controls) was carried out. Dietary data gathered by FFQ were used to calculate flavonoid intake. Adjusted OR and 95 % CI were estimated by logistic regression. No linear association between risk of developing colorectal cancer and total dietary flavonol, procyanidin, flavon-3-ol or flavanone intakes was found, but non-tea flavonol intake was inversely associated with colorectal cancer risk (OR 0.6; 95 % CI 0.4, 1.0). Stratification by site of cancer and assessment of individual flavonols showed a reduced risk of developing colon but not rectal cancer with increasing non-tea quercetin intake (OR 0.5; 95 % CI 0.3, 0.8; P(trend) < 0.01). We concluded that flavonols, specifically quercetin, obtained from non-tea components of the diet may be linked with reduced risk of developing colon cancer.

The intake of flavonoids has been inversely related to the risk of various common neoplasms, but scanty data exist on oral and pharyngeal cancer. We used data from a case-control study conducted in Italy between 1992 and 2005 to examine the relationship between flavonoid intake and oral and pharyngeal cancer risk. The study included 805 cases with incident, histologically confirmed oral and pharyngeal cancer, and 2,081 hospital controls admitted for acute, nonneoplastic conditions. We have applied data on food and beverage content of six major classes of flavonoids, on dietary information collected through a validated food-frequency questionnaire. The odds ratios (OR) were calculated using multiple logistic regression models, conditioned on study center, sex, and age. After adjustment for education, tobacco, alcohol, body mass index, and non-alcohol energy intake, ORs for the highest versus the lowest quintile of intake were 0.51 [95% confidence intervals (95% CI), 0.37-0.71] for flavanones, 0.62 (CI, 0.43-0.89) for flavonols, and 0.56 (95% CI, 0.40-0.78) for total flavonoids. No significant association emerged for isoflavones (OR, 0.90), anthocyanidins (OR, 0.86), flavan-3-ols (OR, 0.84), and flavones (OR, 0.75). The ORs were consistent across strata of age, sex, education, body mass index, tobacco, and alcohol. After allowance for vegetable and fruit consumption, the inverse relations with total flavonoids and flavanones remained significant, whereas that with flavonols became nonsignificant. None of the associations were significant after further allowance for vitamin C, probably on account of the high collinearity between these compounds.

We have examined the role of three classes of flavonoids that are relatively common in the Greek diet (flavanones, flavan-3-ols, and flavonols) in the etiology of lung cancer using data from a case-control study among women, which was undertaken in Athens, Greece, in the late 1980s. Study subjects were 154 women with lung cancer and 145 control women with orthopedic conditions. Women reported their life-long smoking histories and average frequency of consumption, before onset of present disease, of 47 food items or beverages that collectively covered >80% of the intake of each of the energy-providing nutrients. Intakes of flavonoids were calculated using the recently published U.S. Department of Agriculture database. The data were modeled through logistic regression, controlling for energy intake and smoking. There was no indication that intake of any of the studied flavonoid categories reduces the risk of lung cancer; indeed, for flavonols there was an unexpected positive association. Thus, our study does not indicate a protective effect of flavanones, flavan-3-ols, or flavonols on lung cancer risk and indicates that the factors responsible for the protective effect of vegetables and fruits against the risk of this cancer are unlikely to belong to these flavonoid categories.