No abstract

A highly oxygenated chromone, conyzorigun (1 ), from Ageratum conyzoides plants was earlier reported to contain a novel stable ketene acetal system by virtue of an oxygen linkage between the benzopyrone and phenyl moieties. A reinvestigation of this structure in the light of biosynthetic experiments followed by chemical degradation is now described. The results obtained indicate that conytorigun does not contain the above-described oxygen linkage, being a flavone of a known structure, viz. eupalestin (4).Adesogan and Okunade ' have reported the isolation of a new chromone, conyzorigun (l), C, H,,O , , from Ageratum conyoides plants as a minor constituent. This structure was assigned by them on the basis of u.v., i.r., ' H and ' 3C n.m.r. data together with evidence from alkali degradation of the compound which yielded the products (2) and (3). In view of the presence of such an unusual oxygen linkage between the benzopyrone and phenyl moieties, constituting a ketene acetal system, we were interested in the biosynthesis of this compound. M e 0 M e O @ o a o ,

No abstract

Deuteriated benzene-induced shifts [A ppm = S(CDC1,) -S(C,D,)] in the 'H NMR spectra of some naturally occurring polyoxygenated flavones isolated from Ageratum conyzoides and Eupatorium odoraturn have been studied. The downfield shift of the pyrone ring proton H-3, particularly in B-ring methoxylated flavones, is significant; as it is in the opposite direction to that of an aromatic proton it could be of diagnostic value in structural elucidation. The benzene-induced shifts of all the other protons have also been studied.

Durch Chromatografieren von Precocene‐I (I) über mit Trichloressigsäure (II) imprägniertem Aluminiumoxid wird das Dimere (III) erhalten.