Efficient synthesis of polyoxygenated flavones from naturally occurring flavanones

Abstract

Flavonoids are constituents of the human diet (they are present in many beverages and food), and in organisms they are responsible for several biological functions, including that of antioxidant. Because of the increasing interest in these molecules, methods for their synthesis and structural modification are of great importance; studies on the biological activities of many of these compounds are insufficient because of their scarcity and/or high cost. We have developed an expeditious synthesis of polyoxygenated flavones, starting from available and inexpensive flavanones, using a bromination-methoxylation procedure. A series of flavonoids that are not otherwise accessible can be prepared using this method. As an example, 3'-demethoxysudachitin, a limited flavone possessing antimicrobial activity against methicillin-resistant Staphylococcus aureus and Helicobacter pylori and acting as a 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenger, was prepared in fairly satisfactory yield.

Nanoemulsion-based delivery systems for poorly water-soluble bioactive compounds: Influence of formulation parameters on polymethoxyflavone crystallization

“…PMFs and OH-PMFs are phytochemicals that have been isolated from sweet orange peels (Hirata, et al, 2009; Li, Lo, & Ho, 2006), tangerine peels (Wang, Wang, Huang, Tu, & Ni, 2007) and other citrus plants. OH-PMFs can also be chemically synthesized by direct demethylation or hydroxylation of PMFs (Li, et al, 2007) or from basic building blocks such as methoxylated acetophenones and substituted benzoaldehydes (Bovicelli, et al, 2007; Li, et al, 2007; Li, Wang, Sang, Huang, & Ho, 2006; Tsukayama, Kusunoki, Hossain, Kawamura, & Hayashi, 2007). OH-PMFs may also be produced using a microbial-catalyzed de-methylation reaction (Okuno & Miyazawa, 2004).…”

Isolation, modification and cytotoxic evaluation of flavonoids from Rhododendron hainanense

“…To determine the changes of bioactivity resulting from different substituents of A, B ring and the type of C ring, matteucinol ( 1 ) was modified to the target compounds according to the method described in Figure 1. Matteucinol ( 1 ) was oxidized to flavone 9 upon exposure to iodine in DMSO at 100°C in a 95% yield [7] . The demethylation reaction of flavone 9 was carried out using HBr in AcOH to obtain the corresponding 5,7,4′‐trihydroxyflavone 10 [8] .…”

“…Matteucinol (1) was oxidized to flavone 9 upon exposure to iodine in DMSO at 100°C in a 95% yield. [7] The demethylation reaction of flavone 9 was carried out using HBr in AcOH to obtain the corresponding 5,7,4′-trihydroxyflavone 10. [8] Matteucinol was derivatized according to Fujise's mild acetylation to give diacetate 12 as colourless needles.…”

“…[6] The characteristic compounds of the genus Rhododendron are flavonoids, coumarins, and tannins. During our program of screening for antitumour activity of flavonoid compounds from natural sources, the alcoholic (EtOH) extract of the leaves and twigs of R. hainanense led to the isolation of eight flavonoids (1)(2)(3)(4)(5)(6)(7)(8). We found that the content of matteucinol (1) in R. hainanense was high and accounted for 0.166%, and had a weak cytotoxic activity in vitro against the human leukaemia (HL-60) and human hepatoma (SMMC-7721) cell lines.…”

An Improved Synthesis of Apigenin

“…However, the key starting β-ketoester could not be prepared easily and the microwave irradiation signified harsh terms to a number of researchers because of the inconsistent laboratory conditions in China. Apigenin has also been prepared, [6][7][8] but almost all of the published methods have in common, problems of low yields and poorly accessible starting materials.…”