Hydroxycinnamic Acid Conjugates Research Articles

Chemical factors contributing to orosensory profiles of bilberry (Vaccinium myrtillus) fractions

The effects of fractionation on the sensory profile of bilberry (Vaccinium myrtillus) were studied. The berries were fractionated by juice pressing, four ethanol extractions and ethanol evaporation. High-performance liquid chromatography and gas chromatography were used to analyze phenolic compounds, sugars and organic fruit acids of the fractions, and sensory properties of the fractions were studied using generic descriptive analysis. The majority of the phenolic compounds were anthocyanins, and they were mainly found to be located in the press residue. Anthocyanins and other phenolic compounds dissolved in ethanol, and the extracts were perceived as astringent and bitter as the sensory profile of the press residue was very mild. The juice was dominant in sweetness because it contained most of the sugars and fruit acids. Many flavonol glycosides and hydroxycinnamic acid conjugates were discovered to be the compounds contributing to astringency and bitterness, especially myricetin-3-O-arabinoside, myricetin-3-O-glucoside, myricetin-3-O-galactoside and an unknown caffeoyl quinic acid derivative. By supplementing the juice fraction with extracts, the content of phenolic compounds was significantly increased without altering the sensory profile of the juice.

First synthesis, characterization, and evidence for the presence of hydroxycinnamic acid sulfate and glucuronide conjugates in human biological fluids as a result of coffee consumption

A systematic investigation of the human metabolism of hydroxycinnamic acid conjugates was carried out. A set of 24 potential human metabolites of coffee polyphenols has been chemically prepared, and used as analytical standards for unequivocal identifications. These included glucuronide conjugates and sulfate esters of caffeic, ferulic, isoferulic, m-coumaric and p-coumaric acids as well as their dihydro derivatives. A particular focus has been made on caffeic and 3,4-dihydroxyphenylpropionic acid derivatives, especially the sulfate conjugates, for which regioselective preparation was particularly challenging, and have so far never been identified as human metabolites. Ten out of the 24 synthesized conjugates have been identified in human plasma and/or urine after coffee consumption. A number of these conjugates were synthesized, characterized and detected as hydroxycinnamic acid metabolites for the first time. This was the case of dihydroisoferulic acid 3'-O-glucuronide, caffeic acid 3'-sulfate, as well as the sulfate and glucuronide derivatives of 3,4-dihydroxyphenylpropionic acid.

In vitro and in vivo conjugation of dietary hydroxycinnamic acids by UDP-glucuronosyltransferases and sulfotransferases in humans

Hydroxycinnamic acids are a class of phenolic antioxidants found widely in dietary plants. Their biotransformation in the human organism primarily involves Phase II conjugation reactions. In this study, activities of UDP-glucuronosyltransferases (UGTs) and sulfotransferases (SULTs) towards major dietary hydroxycinnamic acids (caffeic, dihydrocaffeic, dihydroferulic, ferulic and isoferulic acids) were investigated. Conjugate formation was evaluated using human liver and intestinal S9 homogenates, and in vitro characterization was carried out using recombinant human UGTs and SULTs. Analysis of the kinetics of hydroxycinnamic acid conjugation in human S9 homogenates revealed that intrinsic clearance ( V max/ K m) is much greater for sulfation than for glucuronidation. Assessment of activity using a panel of recombinant human SULTs showed that SULT1A1 is most active in the sulfation of caffeic, dihydrocaffeic and isoferulic acids, while SULT1E1 is most active in the sulfation of ferulic and dihydroferulic acids. Only isoferulic acid was significantly glucuronidated by human liver S9 homogenates, explained by the high activity of liver-specific UGT1A9. Studies on the kinetics of active SULTs and UGTs demonstrated a markedly lower K m for SULTs. To further corroborate our findings, we carried out an intervention study in healthy humans to determine the hydroxycinnamic acid conjugates in urine after consumption of hydroxycinnamate-rich coffee (200 ml). Analysis showed that sulfates are the main conjugates in urine, with the exception of isoferulic acid, which is mainly glucuronidated. These data suggest that sulfates are the predominant hydroxycinnamic acid conjugates in humans, and that SULT mediated sulfation is a major factor determining the bioavailability of hydroxycinnamic acids in vivo.

Contribution of phenolic compounds to the UV-B screening capacity of developing barley primary leaves in relation to DNA damage and repair under elevated UV-B levels

Epidermally located UV-absorbing hydroxycinnamic acid conjugates and flavonoid glycosides are known to be efficient UV-B protectants in higher plants, although important biological molecules are not always fully protected. However, repair mechanisms also exist, such as repair of damaged DNA by photolyases. To distinguish between the relative importance of the phenolic compounds and of DNA repair, developing primary leaves of two barley lines, mutant ant 30-310, deficient in flavonoids, and its parent line Ca 33787, were grown under relatively high visible light (650–700 μmol m−2 s−1 max for 6 h in a 13 h photoperiod) and supplemented with (+ UV-B) or without (−UV-B) 12 kJ m−2 UV-BBE for 6 h daily. UV-B screening capacity of the leaf phenolics was determined at 315 nm during leaf development and compared with thymine dimers (TD) accumulation, as an indicator of UV-B-induced DNA damage and potential subsequent repair. The degree of damage was related to the phenolic contents of the leaves. UV-B screening capacity was increased ca. 4-fold in the parent line (+ UV-B), mainly due to UV-induced flavonoid (saponarin, lutonarin) accumulation in epidermal and subepidermal mesophyll tissue, relative to the flavonoid-deficient mutant. Nevertheless, in the parent line an 8-fold increase in TD levels occurred over the growth period of 18 days, whereas the mutant accumulated additional DNA damage, with 6- to 9-fold higher TD amounts. Surprisingly, under the high UV-B irradiation, growth and development of the primary leaves in both lines were only slightly reduced.

Distribution of hydroxycinnamic acid conjugates in fruit of commercial eggplant (Solanum melongena L.) cultivars.

There is gathering evidence that antioxidant phytonutrients in fruits and vegetables have health-promoting effects. Eggplant fruit have a high content of antioxidant phenolic compounds. We evaluated the main class of eggplant phenolics, hydroxycinnamic acid conjugates, in the fruit of seven commercial cultivars. Fourteen conjugates were quantified and identified by high-performance liquid chromatography, ES(-)-MS, and (1)H NMR data. Significant differences in their content and composition were evident among cultivars and in tissue from stem, middle, and blossom end segments. Chlorogenic acid (5-O-caffeoylquinic acid) was the predominant compound, and its 3-O-, 4-O-, and 5-O-cis isomers were also present. The 10 other phenolics fell into four groups, including 3,5- and 4,5-dicaffeoylquinic acid isomers, four amide conjugates, two unknown caffeic acid conjugates, and 3-O-acetyl esters of 5-O- and 4-O-caffeoylquinic acid. Dicaffeoylquinic and 3-O-acetyl chlorogenic acids were most variable among the cultivars. Dicaffeoyquinic acids were most abundant in the blossom end, whereas 3-O-acetyl esters were highest in the midsection.

Preparation and biological assessment of hydroxycinnamic acid amides of polyamines

Many plants contain hydroxycinnamic acid conjugates of polyamines that are remarkably similar in general structure to the acylated polyamines found in spider and wasp toxins. In an effort to determine whether these compounds might play a role in the chemical defense of plants against arthropod pests we synthesized a variety of analogues of the coumaric (4-hydroxycinnamic) acid conjugates of di-, tri-, and tetraamines using common protection and acylation strategies. N 1- and N 8-coumaroyl spermidine were tested in feeding trials with insect larvae including the European corn borer ( Ostrinia nubilalis), the tobacco budworm ( Heliothis verescens) and the oblique banded leaf roller ( Choristoneura rosaceana). Antifeedant assays with the rice weevil Sitophilus oryzae were also performed. Neither the naturally occurring coumaric acid conjugates of polyamines nor their analogues showed notable toxicity towards insects, despite precautions to maintain these easily oxidized materials in the wet diet. However, more direct bioassays of these compounds on glutamate dependent neuroreceptors including the deep abdominal extensor muscles of crayfish, or mammalian NMDA, δ2, and AMPA receptors, clearly showed that these compounds were inhibitory. N 1-Coumaoryl spermine, a dodecyl and a cyclohexyl analogue were especially active at NMDA NR1/NR2B receptors. The latter had an IC 50 of 300 μM in the crayfish. N 1-Coumaroyl spermine had an IC 50 in the crayfish preparation of 70–300 μM and against the mammalian NR1/NR2B receptor of 38 nM. Structure–activity variations show similar trends of length and hydrophobicity as has been seen previously with analogues of spider toxins. We conclude from this work that while the coumaric acid polyamine conjugates are active when directly applied to neuroreceptors, they show no overt toxicity when ingested by insect larvae.

Oat antioxidant extraction and measurement - towards a commercial process

Oat flour has preserving properties that have been attributed to the antioxidant activity of phenolic compounds, particularly hydroxycinnamic acid conjugates. This work compares extraction methods based on methanol and propan-2-ol for the removal of oat antioxidants from milled oats. The efficiency of the extraction method was determined by measuring the concentration of total phenolic compounds and the antioxidant activity based on an oxidation reaction of β-carotene with linoleic acid in an emulsion. A novel method was also used based on the quenching of light generated from the chemiluminescence reaction between cytochrome c, tert- butylhydroperoxide (t-BHPO) and luminol. The chemiluminescence method proved to be reliable, rapid and sensitive. Both propan-2-ol and methanol extraction methods yielded oat extracts with antioxidant activity. The propan-2-ol extract contained approximately 70% of the activity measured in the methanol extract. Despite the lower yield, the industrial advantages of the latter method are discussed. © 1999 Society of Chemical Industry

Accumulation Patterns of Polyamines and Hydroxycinnamic Acid Conjugates during Microsporogenesis of Corylus avellana

The am ounts of free, conjugated (hydroxycinnamic acid amides) and insoluble (poly)amines (putrescine, spermidine, spermine) as well as hydroxycinnamic acid esters (quinic acid esters) were determined during development of male inflorescences of Corylus avellana L. The location of these compounds either in sporophytic or gametophytic tissues and the possible correlation of their accumulation with exine formation are discussed.

Phenylpropanoid patterns in fagales pollen and their phylogenetic relevance

The occurrence of hydroxycinnamic acid-spermidine amides and quercetin 3- O-glucosylgalactoside in pollen of Fagales and some other taxa of the Hamamelididae ( sensu Takhtajan and Cronquist) has been investigated. The genera Alnus, Betula, Corylus, and Quercus show characteristic patterns of N 1,N 10-di-( E)-feruloylspermidine, N 1, N 10-di-( E)-feruloylspermidine, N 1, N 10 -( E)-caffeoyl-( E)-feruloylspermidine and several N, N-di- p-coumaroylspermidines. The occurrence of these amides—together with some other unidentified hydroxycinnamic acid conjugates and quercetin 3- O-glucosylgalactoside—in extracts of the pollen grains support suggested relationships among Fagales, Juglandales, and Myricales.

Enzymic Synthesis of Caffeoylglucaric Acid from Chlorogenic Acid and Glucaric Acid by a Protein Preparation from Tomato Cotyledons

The phenylpropane metabolism of tomato (Lycopersicon esculentum Mill) cotyledons was investigated. The HPLC analysis revealed two hydroxycinnamic-acid conjugates as major components, identified as chlorogenic acid (5-O-caffeoylquinic acid) and caffeoylglucaric acid (2-O- or 5-O-caffeoyl-glucaric acid). Quantitative analyses indicated a precursor-product relationship between the chlorogenic and caffeoylglucaric acids. Protein preparations from tomato cotyledons were found to catalyze the formation of caffeoylglucaric acid with chlorogenic acid as acyl donor and free glucaric acid as acceptor molecule. This enzyme activity, possibly to be classified as hydroxycinnamoylquinic acid:glucaric acid hydroxycinnamoyltransferase, acts together with hydroxycinnamoyl-CoA: quinic acid hydroxycinnamoyltransferase.

Coumaroyl-, caffeoyl- and feruloyltartronates and their accumulation in mung bean

Three new plant constituents were isolated from the primary leaves of Vigna radiata (= Phaseolus aureus) and their structures elucidated and characterized with the aid of negative-ion fast atom bombardment mass spectrometry (FAB MS), 1H NMR and UV spectroscopy, thin-layer, gas-liquid and high performance liquid chromatography. The new conjugates are ( E)- p-coumaroyl-, ( E)-caffeoyl- and ( E)-feruloyltartronic acids. Their structures were unequivocally confirmed by comparison with synthetic material. The metabolism of the new hydroxycinnamic acid conjugates in young plants of Vigna radiata is described.