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Ten highly oxygenated flavonoids, including four new compounds, were isolated from the leaves of Dancy tangerine. Six were identified as 5,6,7,3‘,4‘-pentamethoxyflavone (sinensetin) (1), 5,6,7,8,4‘-pentamethoxyflavone (tangeretin) (2), 5,6,7,8,3‘,4‘-hexamethoxyflavone (nobiletin) (3), 5-hydroxy-6,7,3‘,4‘-tetramethoxyflavone (4), 5,7-dihydroxy-6,8,3‘,4‘-tetramethoxyflavone (5), and 5-hydroxy-6,7,8,3‘,4‘-pentamethoxyflavone (5-O-desmethylnobiletin) (6) by direct comparison with authentic samples, comparing their spectroscopic data with those reported in the literature or by simply interpreting their spectral data. The new compounds were elucidated as 5,7,8,3‘,4‘- pentamethoxyflavanone (7), 5,6,7,8,3‘,4‘-hexamethoxyflavanone (8), 7-chloro-3,5,6,8,3‘,4‘-hexamethoxyflavone (9), and 7-chloro-3,5,6,8,4‘-pentamethoxyflavone (10) on the basis of chemical and spectroscopic studies. Keywords: Citrus; Dancy tangerine leaves; polymethoxyflavone; chloride polymethoxyflavone; polymethoxyflavanone

In order to facilitate identification of possible metabolites arising from in vitro action of catechol-O-methyltransferase upon 7,8-dihydroxy- and 8,9-dihydroxy-4-n-propyl-1,2,3,4,4a,5,6,10b-octahydrobenzo[f]quinolines (11, 12), all four possible monomethyl ether derivatives have been synthesized. Incubation of 11 and 12 with the enzyme revealed that the 8,9-dihydroxy positional isomer 12 (which contains the dopamine moiety held in the beta conformation) but not the 7,8-dihydroxy isomer 11 (which holds the dopamine moiety in the alpha conformation) was a substrate for the enzyme. The sole detectable product of 12 was 8-hydroxy-9-methoxy derivative 15 in which the "meta" hydroxy group of the dopamine moiety is etherified.

In order to facilitate identification of possible metabolites arising from in vitro action of catechol-O-methyltransferase upon 7,8-dihydroxy- and 8,9-dihydroxy-4-n-propyl-1,2,3,4,4a,5,6,10b-octahydrobenzo[f]quinolines (11, 12), all four possible monomethyl ether derivatives have been synthesized. Incubation of 11 and 12 with the enzyme revealed that the 8,9-dihydroxy positional isomer 12 (which contains the dopamine moiety held in the beta conformation) but not the 7,8-dihydroxy isomer 11 (which holds the dopamine moiety in the alpha conformation) was a substrate for the enzyme. The sole detectable product of 12 was 8-hydroxy-9-methoxy derivative 15 in which the "meta" hydroxy group of the dopamine moiety is etherified.

The biosynthesis of chromomycin A3 was investigated using 13C-labeled acetates, methionine and glucose, and 13C, 18O-labeled acetate. 13C NMR spectral analysis demonstrated that: Aglycone assembly occurs by combining at least two polyketide chains; three of nine oxygen atoms of the aglycone originate from acetate precursor oxygen atoms; carbon methylations on the aromatic ring at C-7, on the chromose B sugar, and two O-methylations appear to be carried out by S-adenosyl-methionine requiring methyl transferases; and glucose is the precursor for all of the sugars.