Chalcones chemical structure

Flavonoids are secondary metabolites generally occurring in various plants as glycosides. The chemical structure of flavonoids shows high variety. The basic structure of flavons and flavonols is the 2-phenylbenzo-gamma-pyrone. Flavonoids generally contain two phenol rings linked with a linear three-carbon chain (chalcones) or with three carbon... 

Fig. 2.38. Basic chemical structure of flavones, flavonols and flavonoids (chalcones and aurones).

In our analysis of the chemical structures which are active tur-inducers (41) it was found that the compounds fell into four groups (1) acetophenones and related structures, (2) monolignols, (3) hydroxycinnamic acids and their esters, and (4) chalcone derivatives (Fig. 1). Each compound had either a guaiacyl or a syringyl nucleus, and with the exception of the monolignols, possessed a carbonyl group. Most were of common occurrence in vascular plants. 

Chart 8 Chemical structures of the CA4 boronic acid bioisostere (9) and of MDL-27048. The former was proposed by a structure-based molecular modeling study, the latter was used to elaborate a virtual screening protocol for the identification of novel chalcone CSI... 

In solution, the anthocyanins actually might exist in equilibrium with essentially four molecular forms - the flavylium cation, the quinoidal base, the hemiacetal base and chalcone [19]. The relative amounts of the four structure forms depends on both the pH and the difference in structure of the anthocyanins [20-22], Generally, anthocyanins exist primarily as the stable flavylium cation above pH 2. This uniqueness in the chemical structure is one of the important key factors affecting their absorption, metabolism, bioavailability and, consequently, the biological responses of the human body to anthocyanins. 

Examination of the chemical structures of the five chalcones revealed that... 

Improvements in the instrumentation, ionization sources, high-resolution mass analyzers, and detectors [67-69], in recent years have taken mass spectrometry to a different level of HPLC-MS for natural product analysis. Mass spectrometry detection offers excellent sensitivity and selectivity, combined with the ability to elucidate or confirm chemical structures of flavonoids [70-72]. Both atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) are most commonly used as ionization sources for flavonoid detection [73-76]. Both negative and positive ionization sources are applied. These sources do not produce many fragments, and the subsequent collision-induced dissociation energy can be applied to detect more fragments. Tandem mass spectrometry (MS , n> 2) provides information about the relationship of parent and daughter ions, which enables the confirmation of proposed reaction pathways for firagment ions and is key to identify types of flavonoids (e.g., flavones, flavonols, flavanones, or chalcones) [77-80]. 

Fig. 18.3. Chemical structures of polyphenols Hydroxybenzoic acids (Hba), Hydroxy cinammic acids (Hca), Flavonoids (F), Chalcones (C), Stilbenes (S, cf. 20.2.6.6), Lignans (L). R H, OH or OCH3...

Among the most intensively investigated of all the chalcone Diels Alder adducts are a group obtained solely from Morus species in which the diene component of the reaction is a dehydroprenylflavanone. The structures of several such compounds published prior to 1992 have now been revised on the basis of new spectroscopic and chemical data. Among the most important of the techniques used were two-dimensional NMR and circular dichroism spectroscopy. The revised structures listed in Table 16.5 are those of sanggenons C (210), D (211), E (212), and O (213). In these compounds, the flavanones show the common feature... 

Table 5.38 b. Structures and 13C Chemical Shifts (<5C in ppm) of Selected Chalcones, Flavones, Flavonols, Isoflavones, Dihydro-flavones, Dihydroflavonols and Flavons (Aglycones). Spectra were Recorded in DMSO-d6, Except those of Flavone (CDC13) and 2 -Hydroxy-, and 2,2 -Dihydroxychalcone (D20/DMS0-d6 (2 7)) [989, 990]. 

The first PKS crystal structure, that of alfolfa chalcone synthase (CHS) in 1999 (6), had previously revealed foe type III PKS internal active site cavity and conserved Cys/His/Asn catalytic triad responsible for starter substrate loading and iterative polyketide extension (6). CHS provides the first committed chemical intermediate in flavonoid biosynthesis by catalyzing foe sequential decarboxylative addition of three acetate units from maionyl-CoA to a p-... 

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