- Degradation of ascorbic acid in ethanolic solutions
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Ascorbic acid occurs naturally in many wine-making fruits. The industry also uses ascorbic acid as an antioxidant and color stabilizer in the making of alcoholic beverages including white wine, wine cooler, alcopop, and fruit liqueur. However, the degradation of ascorbic acid itself may cause browning and the deterioration of color quality. This study was aimed to monitor the degradation of ascorbic acid, the formation of degradation products, and the browning in storage of ascorbic acid containing 0-40% (v/v) ethanolic solutions buffered at pH 3.2 as models of alcoholic beverages. The results show that ascorbic acid degradation in the ethanolic solutions during storage follows first-order reaction, that the degradation and browning rates increase with the increase of ethanol concentration, that the activation energy for the degradation of ascorbic acid is in the range 10.35-23.10 (kcal/mol), that 3-hydroxy-2-pyrone is an indicator and a major product of ascorbic acid degradation, and that aerobic degradation pathway dominants over anaerobic pathway in ascorbic acid degradation in ethanolic solutions.
- Hsu, Hsin-Yun,Tsai, Yi-Chin,Fu, Chi-Chang,Wu, James Swi-Bea
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- Pyrone Synthesis from Renewable Sources: Easy Preparation of 3-Acetoxy-2-oxo-2H-pyran-6-carboxylic Salts and their Derivatives as 3-Hydroxy-2H-pyran-2-one from C6 Aldaric Acids
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2-Pyrones are compounds present in several natural products and represent interesting building blocks for the preparation of intermediates in organic syntheses. For these reasons, many different preparation protocols have been developed for the synthesis of pyrone moieties. In this work, a green approach toward the synthesis of those compounds starting from C6 aldaric acids has been investigated. These products are an interesting and versatile class of poly functional C6 units coming from renewable sources. In this paper, we report a green procedure based on a reaction with acetic anhydride under different pH conditions to convert mucic acid and glucaric acid salts into the 3-acetoxy-2-oxo-2H-pyran-6-carboxylic acid salts and their derivatives. The salts, in the presence of hydrochloric acid, are quantitatively converted into the corresponding 3-hydroxy-2-oxo-2H-pyran-6-carboxylic acid, which afforded 3-hydroxy-2H-pyran-2-one in very high yield by further thermal decarboxylation. Crystal structure of the five membered ring lactone intermediate is reported.
- Citterio, Attilio,Gambarotti, Cristian,Leonardi, Gabriella,Li, Jiemeng,Righetti, Grazia Isa C.,Sebastiano, Roberto,Terraneo, Giancarlo,Truscello, Ada M.
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- Total synthesis of the Cephalotaxus norditerpenoids (±)-cephanolides A-D
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Concise syntheses of the Cephalotaxus norditerpenoids cephanolides A-D (8-14 steps from commercial material) using a common late-stage synthetic intermediate are described. The success of our approach rested on an early decision to apply chemical network analysis to identify the strategic bonds that needed to be forged, as well as the efficient construction of the carbon framework through iterative Csp2-Csp3 cross-coupling, followed by an intramolecular inverse-demand Diels-Alder cycloaddition. Strategic late-stage oxidations facilitated access to all congeners of the benzenoid cephanolides isolated to date.
- Haider, Maximilian,Sennari, Goh,Eggert, Alina,Sarpong, Richmond
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supporting information
p. 2710 - 2715
(2021/03/01)
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- Regioselective Formation of Substituted Indoles: Formal Synthesis of Lysergic Acid
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A Diels–Alder reaction-based strategy for the synthesis of indoles and related heterocycles is reported. An intramolecular cycloaddition of alkyne-tethered 3-aminopyrones gives 4-substituted indolines in good yield and with complete regioselectivity. Additional substitution is readily tolerated in the transformation, allowing synthesis of complex and non-canonical substitution patterns. Oxidative conditions give the corresponding indoles. The strategy also allows the synthesis of carbazoles. The method was showcased in a formal synthesis of lysergic acid.
- Beaudry, Christopher M.,Points, Gary L.,Stout, Kenneth T.
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supporting information
p. 16655 - 16658
(2020/12/01)
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- Enantioselective Total Synthesis of (+)-Iso-A82775C, a Proposed Biosynthetic Precursor of Chloropupukeananin
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(+)-Iso-A82775C is a proposed biosynthetic precursor of the chloropupukeananin family and an important intermediate for related natural products. The first enantioselective total synthesis of (+)-iso-A82775C (18 steps, 2.2% overall yield) toward the eventual biomimetic total synthesis of chloropupukeananin is described. The key steps are (1) the enantioselective Diels-Alder reaction of 4-bromo-3-hydroxy-2-pyrone with methyl 2-chloroacrylate using cinchonine as an organocatalyst and (2) the anti-selective Cu-mediated SN2′ reaction to afford the axially chiral vinylallene moiety.
- Suzuki, Takahiro,Watanabe, Soichiro,Kobayashi, Susumu,Tanino, Keiji
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supporting information
p. 922 - 925
(2017/02/26)
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- Elucidating the formation pathway of the off-flavor compound 6-propylbenzofuran-7-ol
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In a previous work, we identified 6-propylbenzofuran-7-ol as an off-flavor compound formed from ascorbic acid and (E)-hex-2-enal in a test apple beverage. In this study, we elucidate the pathway by which 6-propylbenzofuran-7-ol formed. Isotope labeling studies revealed that the propyl group of 6-propylbenzofuran- 7-ol derives from (E)-hex-2-enal and that 6-propylbenzofuran-7-ol contains carbons 2-6 of ascorbic acid. Two compounds, namely, 2,3-dihydro-6- propylbenzofuran-3,7-diol and 3-(2-furoyl)hexanal, were identified as byproducts of a model reaction of ascorbic acid and (E)-hex-2-enal. Each of these compounds was dissolved in an aqueous solution of citric acid and stored at 60 °C for 1 week. After storage, 6-propylbenzofuran-7-ol was detected from a solution of 2,3-dihydro-6-propylbenzofuran-3,7-diol, but not from 3-(2-furoyl)hexanal. 6-Propylbenzofuran-7-ol was formed by isolating tricyclic hemiacetal lactone derived from the Michael addition of ascorbic acid to (E)-hex-2-enal, mixing the tricyclic hemiacetal lactone with the aqueous solution of citric acid, and applying heat. This confirmed that 6-propylbenzofuran-7-ol was formed via the Michael adduct.
- Sakamaki, Kensuke,Ishizaki, Susumu,Ohkubo, Yasutaka,Tateno, Yoshiyuki,Nakanishi, Akira,Fujita, Akira
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p. 9967 - 9973,7
(2020/09/15)
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- A concise access to 3-substituted 2-pyrones
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The development of a modular synthesis of 3-substituted-2-pyrones is described. The attainment of this strategy hinges on a new electrophilic pyrone derivative which can be readily prepared on a multigram scale and which performs very competently in metal-catalyzed cross-coupling reactions with a variety of nucleophiles.
- Frebault, Frederic,Oliveira, Maria Teresa,Woestefeld, Eckhard,Maulide, Nuno
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scheme or table
p. 7962 - 7965
(2011/02/22)
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- Antiatherosclerotic and antithrombotic 2-amino-6-phenyl-4H-pyran-4-ones
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This invention relates to compounds of Formula I STR1 which are useful as antiatherosclerotic agents and inhibitors of cell proliferation for the treatment of proliferative diseases. In addition, various compounds of Formula I are useful inhibitors of platelet aggregation.
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