The hidden face of food phenolic composition

Plant polyphenols are extremely diverse, due to the occurrence of several basic structures, numerous substitutions and, for some groups, of polymers (tannins). Plant polyphenol composition depends on the plant species and organ, with some molecules specific of particular plant families while others are ubiquitous. The polyphenol content is classically assessed by global analysis methods, which lack specificity and accuracy. These methods have been replaced with high performance liquid chromatography (HPLC), that enables accurate determination of individual molecules, provided they can be unambiguously identified and calibration curves can be established. However, HPLC analysis is restricted to simple compounds and difficult to apply in the case of complex extracts. Further difficulties encountered in the case of polymers include irreversible adsorption on the stationary phases. Proanthocyanidin analysis by HPLC after acid-catalysed depolymerisation in the presence of a nucleophile permits to overcome these problems and shows that proanthocyanidins predominate in the polyphenol composition of most plants. Large varietal differences in tannin quantitative and qualitative composition were observed for all plant species studied. Moreover, analysis is usually performed after extraction, which may lead to significant underestimation of the polyphenol content, since a large proportion is not extracted by usual solvents. This may be due to covalent binding to other plant constituents and to non-covalent adsorption on plant solids. Such matrix effect also influences the taste perception of polyphenols and their fate in the digestive tract, from in-mouth interactions with salivary proteins to their metabolism by colon microflora, with potential influence on bioavailability.     

Chemical constituents from Celastrus aculeatus Merr.

Phytochemical investigation of Celastrus aculeatus Merr. led to the isolation of nine compounds. Their structures were identified to be dulcitol (1), β-sitosterol (2), n-tritriacontane (3), nimbidiol (4), pristimerin (5), p-hydroxybenzoic acid (7), vanillic acid (8), 3, 5-dimethoxy-4-hydroxybenzoic acid (9) and a new compound named pristimerol (6) on the basis of mass and NMR spectra. This is the first report of phenolic acids (compounds 7–9) from C. aculeatus Merr. We present the HR-MS, 1D NMR (¹H, ¹³C NMR, DEPT) and 2D NMR (HMBC) data of the new compound (6).     

Chemical constituents from Artemisia argyi and their chemotaxonomic significance

Twelve compounds, including one monoterpene (1), two sesquiterpene lactones (2–3), six flavonoids (4–9), one phenolic glycoside (10), one chromone (11) and one phenolic acid (12), were isolated and identified from the leaves of Artemisia argyi. Compounds 1–2, 4 and 6–7 have not been recorded before in this plant. Compounds 3, 9 and 11 were isolated from the genus Artemisia for the first time. This paper is the first report on the presence of compound 10 in species of Asteraceae. In addition, the chemotaxonomic significance of these compounds was summarized.     

Glycoconjugates are stage- and position-specific cell surface molecules in the developing olfactory system, 1: The CC1 immunoreactive glycolipid defines a rostrocaudal gradient in the rat vomeronasal system

Primary sensory neurons in the vomeronasal organ (VNO) project axons to the glomeruli of the accessory olfactory bulb (AOB) where they form connections with mitral cell dendrites. We demonstrate here that monoclonal antibodies to specific carbohydrate antigens define stage- and position-specific events during the development of the vomeronasal system (VN). CC1 monoclonal antibodies react with specific N-acetyl galactosamine containing glycolipids. In the embryo, CC1 antigens are expressed throughout the VNO and on vomeronasal nerves. Beginning approximately at birth and continuing into adults, CC1 expression is spatially restricted in the VNO to centrally located cell bodies. In the postnatal AOB, CC1 is expressed in the nerve layer and glomeruli, but only in the rostral half of the AOB. These data suggest that CC1 antigens may participate in the targeting of axons from centrally located VNO neurons to rostral glomeruli in the AOB. In contrast, CC2 monoclonal antibodies, which recognize complex α-galactosyl and α-fucosyl glycoproteins and glycolipids, react with all VNO cell bodies and VN nerves from embryonic (E) day 15 to adults. CC2 antibodies do not distinguish rostral from caudal regions of the AOB, nor are the CC2 glycoconjugates developmentally regulated. P-Path monoclonal antibodies, which recognize 9-O-acetyl sialic acid, react with cell bodies in the VNO and nerve fibers from E13 to postnatal (P) day 2. P-Path immunoreactivity disappears from the VNO system almost completely by P14, when only a few P-Path reactive nerve fibers can be seen. These studies suggest that specific cell surface glycoconjugates may participate in spatially and temporally selective cell–cell interactions during development and maintenance of vomeronasal connections.     

A chemosystematic study of the genus Gomphostemma and related genera (Lamiaceae)

Species in the genera Gomphostemma, Chelonopsis and Bostrychanthera were systematically studied with reference to their flavonoid and phenolic acid compounds in order to investigate whether the profiles of these compounds would support a classification of the genus and related genera based on morphological characters. Thirty-five flavonoid glycosides, eight phenolic acids and derivatives were identified by LC-UV-MS/MS analysis of aqueous 80% MeOH extracts on the basis of their UV and mass spectra, retention times and comparison with in-house library. The occurrence of individual compounds was not particularly informative in Gomphostemma, although the overall chemical profile supported G. subgen. Pogosiphon and vicenin-2 was a characteristic component of Gomphostemma leptodon and Gomphostemma curtisii. In contrast, the flavonoids and phenolic acids of Chelonopsis were informative at infrageneric level. Glycosides of 6-substituted flavones were well represented in Ch. subgen. Aequidens, including Ch. forrestii, Ch. rosea, Ch. odontochila, Ch. lichiangensis and C. giraldii. A dicaffeoylquinic acid was produced in Ch. subgen. Chelonopsis, (for example, in Ch. longipes and Ch. Moschata), but absent from Ch. subgen. Aequidens. The same dicaffeoylquinic acid was also found in the genus Bostrychanthera and suggests a close relationship with Ch. subgen. Chelonopsis, in agreement with a recent DNA based phylogeny. There is correlation between trichome type and phenolic acid compound distribution in Chelonopsis, but this is not observed in Gomphostemma.     

Enhanced production of the pharmaceutically important polyphenolic compounds in Vitex agnus castus L. shoot cultures by precursor feeding strategy

Agitated Vitex agnus castus L. shoot cultures were established to analyse the content of selected pharmaceutically important flavonoids and phenolic acids. Two variants (selected from nine ones) of MS medium were prepared: A (BAP 1 mg/L; NAA 0.5 mg/L; GA₃ 0.25 mg/L) and B (BAP 2 mg/L; NAA 0.5 mg/L). The biomass was harvested after 1, 2, 3,4, 5 and 6 weeks. Four‐week cultures (variant A) were selected to perform the precursor feeding experiment. The L‐phenylalanine dose of 1.6 g/L appears to be the most advantageous. Compared to the control cultures, the content of the individual compounds increased in a range from 1.4 to 17.3‐fold (e.g. p‐coumaric acid – 17.3 fold; casticin – 4.8‐fold). The biomass from in vitro cultures is richer in neochlorogenic acid (16‐fold), p‐coumaric acid (5.3‐fold), rutin (2.8‐fold), caffeic acid (1.5‐fold) and cinaroside (1.5‐fold) than the leaves of its parent greenhouse‐cultivated plants. Extracts contained 30 mg/100 g DW of casticin, but after the hydrolysis its amount increased up to 200 mg/100 g DW and twice exceeded the content in the greenhouse leaves. The results indicate that V. agnus castus agitated shoot cultures might be considered as a potential biotechnological source of some pharmaceutically important compounds, especially casticin, rutin, neochlorogenic and p‐coumaric acids.     

Anti-HSV-1, antioxidant and antifouling phenolic compounds from the deep-sea-derived fungus Aspergillus versicolor SCSIO 41502

Chemical investigation of the deep-sea-derived fungus Aspergillus versicolor SCSIO 41502 resulted in the isolation of three new anthraquinones, aspergilols G-I (1–3), one new diphenyl ether, 4-carbglyceryl-3,3′-dihydroxy-5,5′-dimethyldiphenyl ether (4), and one new benzaldehyde derivative, 2,4-dihydroxy-6-(4-methoxy-2-oxopentyl)-3-methylbenzaldehyde (5), along with 23 known phenolic compounds (6–28). The structures of new compounds were elucidated by extensive spectroscopic analysis. The absolute configuration of 3 was established by CD spectrum and the modified Mosher method. Compounds 2, 3 and 9 had evident antiviral activity towards HSV-1 with EC₅₀ values of 4.68, 6.25, and 3.12 μM, respectively. Compounds 15, 18, 20 and 22–24 showed more potent antioxidant activity than l-ascorbic acid with IC₅₀ values of 18.92–52.27 μM towards DPPH radicals. Comparison of the structures and antioxidant activities of 1–28 suggests that the number of phenolic hydroxyl group that can freely rotate can significantly affect the antioxidant activity of phenolic compounds. In addition, 4, 22–24 and 27 had significant antifouling activity against Bugula neritina larval settlement with EC₅₀ values of 1.28, 2.61, 5.48, 1.59, and 3.40 μg/ml, respectively.     

Synthesis and structure–activity relationship studies of phenolic hydroxyl derivatives based on quinoxalinone as aldose reductase inhibitors with antioxidant activity

To enhance aldose reductase (ALR2) inhibition and add antioxidant ability, phenolic hydroxyl was introduced both to the quinoxalinone core and C3 side chain, resulting in a series of derivatives as ALR2 inhibitors. Biological activity tests suggested that most of the derivatives were potent and selective inhibitors with IC₅₀ values ranging from 0.059 to 6.825 μM, and 2-(3-(4-hydroxystyryl)-7-methoxy-2-oxoquinoxalin-1(2H)-yl)acetic acid (6b) was the most active. Particularly, it was encouraging to find that some derivatives endowed with obvious antioxidant activity, and among them the phenolic 3,4-dihydroxyl compound 6f with 7-hydroxyl in the quinoxalinone core showed the most potent activity, even comparable with the well-known antioxidant Trolox. Structure-activity relationship and docking studies highlighted the importance of phenolic hydroxyl both in C3 side chain and the core structure for constructing potent ALR2 inhibitors with antioxidant activity.