Conjugation of Oxidized Betanidin and Gomphrenin Pigments from Basella alba L. Fruits with Glutathione

Identification and reactivity of pigments in prominent vegetable leaves of Basella alba L. var. 'Rubra' (Malabar spinach)

The unique profiles of betacyanins as well as their stability and antioxidant activity in purple leaf extracts of the fast-growing, soft-stemmed vine Basella alba L. var. 'Rubra', known as Malabar spinach, are partly characterized for the first time. The distribution of gomphrenin and its acylated derivatives in the leaves is completely different from the profiles of the pigments in the fruits. The most abundant acylated pigment in leaves (24%) turned out 6'-O-E-sinapoyl-gomphrenin (gandolin), however, the most significant difference in the pigment profiles is a presence of two novel pigments tentatively identified as highly abundant 6'-O-(3,4-dimethoxy-E-cinnamoyl)-gomphrenin and 6'-O-(3,4,5-trimethoxy-E-cinnamoyl)-gomphrenin as well as their isoforms. Significant degradation of the pigments in the fruit extracts under the impact of selected metal cations and UV-Vis irradiation as well as high protective activity of the leaf extract matrix were observed. Partial chromatographic purification of the leaf extract resulted in an increase of the pigment concentration which was correlated positively with the increased antioxidant activity of obtained fractions.

Basella alba L. (Malabar Spinach) as an Abundant Source of Betacyanins: Identification, Stability, and Bioactivity Studies on Natural and Processed Fruit Pigments

The antioxidant and anti-inflammatory activities of acylated and decarboxylated gomphrenins, as well as Basella alba L. fruit extract, were investigated in relation to gomphrenin, known for its high biological potential. The most abundant natural acylated gomphrenins, namely, 6'-O-E-caffeoyl-gomphrenin (malabarin) and 6'-O-E-4-coumaroyl-gomphrenin (globosin), were isolated from B. alba extract for the studies. In addition, controlled thermal decarboxylation of gomphrenin in the purified B. alba extract at 65-75 °C resulted in the formation of the most prevalent decarboxylated products, including 17-decarboxy-gomphrenin and 2,17-bidecarboxy-gomphrenin, along with their isoforms. The structures of the decarboxylated pigments were confirmed by NMR analyses. Exploring the matrix effect on pigment reactivity revealed a tremendous increase in the stability of all betacyanins after the initial stage of extract purification using a cation exchanger under various conditions. This indicates the removal of a substantial portion of the unfavorable matrix from the extract, which presumably contains reactive species that could otherwise degrade the pigments. Furthermore, the high concentration of citrates played a significant role in favoring the formation of 2-decarboxy-gomphrenin to a considerable extent. In vitro screening experiments revealed that the tested compounds demonstrated strong anti-inflammatory properties in lipopolysaccharide (LPS)-activated human macrophages. This effect encompassed the selective inhibition of cytokine and chemokine release from activated macrophages, modulation of the chemotactic activity of immune cells, and the regulation of tissue remodeling mediators' release.

Unveiling Alternative Oxidation Pathways and Antioxidant and Cardioprotective Potential of Amaranthin-Type Betacyanins from Spinach-like Atriplex hortensis var. 'Rubra'

A comprehensive oxidation mechanism was investigated for amaranthin-type betacyanins with a specific glucuronosylglucosyl moiety isolated from Atriplex hortensis 'rubra' using liquid chromatography coupled to diode array detection and electrospray ionization tandem mass spectrometry (LC-DAD-ESI-MS/MS) and LC-Quadrupole-Orbitrap-MS (LC-Q-Orbitrap-MS). By employing one-dimensional (1D) and two-dimensional (2D) NMR, this study elucidates the chemical structures of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS)-oxidized celosianins for the first time. These findings demonstrate alternative oxidation pathways for acylated betacyanins compared to well-known betanidin, betanin, and gomphrenin pigments. Contrary to previous research, we uncover the existence of 17-decarboxy-neo- and 2,17-bidecarboxy-xanneo-derivatives as the initial oxidation products without the expected 2-decarboxy-xan forms. These oxidized compounds demonstrated potent free radical scavenging properties. Celosianin (IC50 = 23 μg/mL) displayed slightly higher antioxidant activity compared to oxidized forms, 17-decarboxy-neocelosianin (IC50 = 34 μg/mL) and 2,17-bidecarboxy-xanneocelosianin (IC50 = 29 μg/mL). The oxidized compounds showed no cytotoxic effects on H9c2 rat cardiomyoblasts (0.1-100 μg/mL). Additionally, treatment of H9c2 cells with the oxidized compounds (0.1-10 μg/mL) elevated glutathione levels and exhibited protective effects against H2O2-induced cell death. These findings have significant implications for understanding the impact of oxidation processes on the structures and biological activities of acylated betalains, providing valuable insights for future studies of the bioavailability and biological mechanism of their action in vivo.

Structural Studies on Diverse Betacyanin Classes in Matured Pigment-Rich Fruits of Basella alba L. and Basella alba L. var. ‘Rubra’ (Malabar Spinach)

Identification of betacyanins in Basella alba L. and Basella alba L. var. ‘Rubra’ fruits was performed by low- and high-resolution mass spectrometry (LRMS and HRMS) as well as ¹H, ¹³C and two-dimensional NMR which revealed hitherto completely not known betacyanin classes in the plant kingdom. Especially, the presence of unique nitrogenous acyl moieties in the structures of the pigments was ascertained by the HRMS Orbitrap detection. Except for detected polar betacyanin glycosylated derivatives, presence of a series of previously not reported pigments such as malonylated betanidin 6-O-β-glusosides with their acyl migration isomers along with the evidence of the 3′′-hydroxy-butyrylated betacyanins is reported. The first complete NMR data were obtained for novel and principal acylated gomphrenins with hydroxycinnamic acids: 6′-O-E-caffeoyl-gomphrenin (malabarin), 6′-O-E-sinapoyl-gomphrenin (gandolin), 6′-O-E-4-coumaroyl-gomphrenin (globosin) and 6′-O-E-feruloyl-gomphrenin (basellin).

Dehydrogenation of Betacyanins in Heated Betalain-Rich Extracts of Red Beet (Beta vulgaris L.)

Betacyanins are a group of water-soluble red-violet compounds containing nitrogen in their structure. These are biosynthesized in red beetroot (Beta vulgaris L.), a widely consumed vegetable that contains significant amounts of nutritious and bioactive compounds which are also found in dietary supplements. This contribution presents results of betacyanin thermal oxidation (resulting in dehydrogenation) interrelated with decarboxylation in selected acetate/phosphate buffers at pH 3–8 and at 85 °C, which may be of particular significance for formulation and performance of foods. Most of the reaction products were detected at the highest concentrations in the acidic solutions (pH 3–4). The main dehydrogenation reaction pathways were monitored by LC-DAD-MS/MS and were associated with decarboxylation of the principal extract pigments, betanin/isobetanin and neobetanin, at carbon positions C-2 and C-17. Additional reactions are accompanied by the 2,15-decarboxylation processes at different dehydrogenation levels with 15-decarboxy-betanin and 2,15-bidecarboxy-betanin, structurally elucidated by NMR analysis, as the distinct indicators of this route type. For other novel pigments detected, 2,15-bidecarboxy-xanbetanin, 2,15-bidecarboxy-xanneobetanin and 2,15,17-tridecarboxy-neobetanin, additional high resolution mass spectrometric analyses were performed and confirmed their molecular formulas.

Multi-colored shades of betalains: recent advances in betacyanin chemistry

Covering: 2001 to 2021Betacyanins cover a class of remarkable natural red-violet plant pigments with prospective chemical and biological properties for wide-ranging applications in food, pharmaceuticals, and the cosmetic industry. Betacyanins, forming the betalain pigment group together with yellow betaxanthins, have gained much attention due to the increasing social awareness of the positive impact of natural products on human health. Betalains are commercially recognized as natural food colorants with preliminarily ascertained, but to be further investigated, health-promoting properties. In addition, they exhibit a remarkable structural diversity based on glycosylated and acylated varieties. The main research directions for natural plant pigments are focused on their structure elucidation, methods of their separation and analysis, biological activities, bioavailability, factors affecting their stability, industrial applications as a plant-based food, natural colorants, drugs, and cosmetics as well as methods for high-yield production and stabilization. This review covers period of the last two decades of betacyanin research. In the first part of the review, we present an updated classification of all known betacyanins and their derivatives identified by chemical means as well as by mass spectrometric and NMR techniques. In the second part, we review the current research reports focused on the chemical properties of the pigments (decarboxylation, oxidation, conjugation, and chlorination reactions as well as the acyl group migration phenomenon) and describe the semi-synthesis of natural and artificial fluorescent betalamic acid conjugates, showing various prospective research directions.

Bioactive Diarylheptanoids from Alpinia coriandriodora

Eight new diarylheptanoids, coriandralpinins A-H (1-8), were isolated from the rhizomes of Alpinia coriandriodora, an edible plant of the ginger family. Their structures, including the absolute configurations, were established by extensive spectroscopic analysis and ECD calculations. Compounds 1-8 have a 1,5-O-bridged diarylheptanoid structure featuring polyoxygenated aryl units. When evaluated for intracellular antioxidant activity using t-BHP stressed RAW264.7 macrophages, all these compounds scavenged reactive oxygen species (ROS) in a concentration-dependent manner. Compounds 3 and 5 also showed inhibitory activity against NO release in LPS-induced RAW 264.7 cells. Six known flavonols, 7,4'-di-O-methylkaempferol, 7-O-methylquercetin, 7,4'-di-O-methylquercetin, 7,3',4'-tri-O- methylquercetin, kaempferol 3-O-β-D-(6-O-α-L-rhamnopyranosyl)glucopyranoside, and 3-O-β-D-glucopyranuronosylquercetin were also isolated and characterized from the rhizomes.

The Responses of Bioactive Betanin Pigment and Its Derivatives from a Red Beetroot (Beta vulgaris L.) Betalain-Rich Extract to Hypochlorous Acid

Neutrophils produce hypochlorous acid (HOCl) as well as other reactive oxygen species as part of a natural innate immune response in the human body; however, excessive levels of HOCl can ultimately be detrimental to health. Recent reports suggest that betacyanin plant pigments can act as potent scavengers of inflammatory factors and are notably effective against HOCl. Comparison of the in vitro anti-hypochlorite activities of a novel betalain-rich red beetroot (Beta vulgaris L.) extract with its pure betalainic pigments revealed that the extract had the highest anti-hypochlorite activity, far exceeding the activity of all of the betalainic derivatives and selected reference antioxidants. This suggests that it may be an important food-based candidate for management of inflammatory conditions induced by excessive HOCl production. Among all pigments studied, betanidin exhibited the highest activity across the pH range.

Identification of Novel Low-Weight Sulfhydryl Conjugates of Oxidized 5-O- and 6-O-Substituted Betanidin Pigments

The formation of conjugates of oxidized betacyanin pigments with selected low-weight sulfhydryl scavengers was studied. Short-lived quinonoids, quinone methides, and aminochromes derived from oxidized betacyanins are able to form adducts with different efficiencies. In this report, mass spectrometric and NMR identifications of CS-linked conjugates of cysteine, cysteamine, N-acetylcysteine, and dl-dithiolthreitol with quinonoid forms generated through oxidation of betanidin, betanin, and gomphrenin is presented. An adduct that formed between cysteine and quinonoid generated from betanin by its oxidation and decarboxylation (2-decarboxy-xanbetanin) was detected and reported for the first time. The most stable gomphrenin CS-conjugate, N-acetylcysteinylated gomphrenin, was isolated by semipreparative chromatography and its structure was established by NMR analysis. This enabled to confirm the conjugation position at carbon C-4 and to indicate the presence of a dopachromic intermediate during oxidation of gomphrenin. Conjugation of betacyanins with thiol-bearing moieties may generate new molecules with modified chemical and biological properties. Obtained results confirm that gomphrenin is capable of forming CS-conjugates with higher efficiency than betanin.

Alternative Mechanisms of Betacyanin Oxidation by Complexation and Radical Generation

The use of natural pigments such as betalains in food and health-related products is often limited by said pigments' relative oxidative stabilities in the products or physiological matrices. Determination of the mechanism of oxidation may inform future development and delivery of better stabilized molecules for improved outcomes. In order to best determine the oxidation mechanism of betanin, a natural food colorant, our efforts were directed toward structural elucidation (LCMS-IT-TOF and NMR) of previously tentatively identified key dehydrogenation products that had been generated as a result of betanin, decarboxylated betanin, and neobetanin oxidation by 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radicals. The resultant oxidation products, the neo-derivatives, were the most stable and survived the preparative isolation and purification process. Structural analyses subsequently confirmed that these compounds, as well as neobetanin, were also the key products of alternative pathways of betanin and 2-decarboxy-betanin oxidation when catalyzed by Cu²⁺ cations in aqueous solutions at pH close to neutral. Therefore, the structures of the following five neo- or xanneo-derivatives (14,15- or 2,3,14,15-dehydrogenated derivatives, respectively) were confirmed: neobetanin, 2-decarboxy-neobetanin, 2-decarboxy-xanneobetanin, 2,17-bidecarboxy-xanneobetanin, and 2,15,17-tridecarboxy-xanneobetanin. This research confirmed that Cu²⁺-catalyzed oxidation of betanin and 2-decarboxy-betanin results in generation of neo-derivatives of betanin. In contrast, Cu²⁺-catalyzed oxidation of 17-decarboxy-betanin and 2,17-bidecarboxy-betanin resulted mostly in formation of betanin xan-derivatives. A relevant mechanism of Cu²⁺-catalyzed oxidation of the pigments is proposed herein that suggests that the oxidation of betanin can possibly occur in the region of the dihydropyridinic ring and can omit the stage of methide quinone formation in the dihydroindolic system.