Luteolin, synthesis

Flavanoids and isocoumarin are common substructures found in many natural products. Palladium-catalyzed carbonylation reactions were applied in the synthesis of luteolin [129] and thunberginol A [130] as well (Scheme 10.41). 

The carbonylative coupling of an alkynyl zinc reagent 4.18 with a highly substituted, electron-rich aryl iodide 4.17 was used in a short synthesis of luteolin 4.20, a flavanoid natural product (Scheme 4.11). After the coupling, employing the PEPPSI catalyst, selective crr/tc-deprotection and 6-endo cyclization yielded the natural product."... 

One of the last steps in flavonoid synthesis is methylation and an 0-methyl-transferase for this has been purified 82-fold from cell suspiension cultures of parsley. It has a pH optimum of 9.7, requires Mg, and the molecular weight is ca. 48000. Unlike catechol methylase from animal tissues, it is not inhibited by p-chloromercuribenzoate or by iodoacetamide. Luteolin (27) and its 7-glucoside were the best substrates, giving chrysoeriol (28) and its 7-gluco-side respectively K values were 4.6 x 10" and 3.1 x 10 moll Erio-dictyol and caffeic acid were poor substrates (K values 1.2 x 10 and 1.6 X 10 moll , respectively) and the enzyme was quite spteciflc for catechols and only 0-methylated a m-hydroxy-group. 

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