J’hytochemistry, Vol. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 21, No. 12, pp. 2965-2967, 1982. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGF 0031-9422/82/122965-03$03.00/O Printed in Great Britain. @ 1982 Pergamon Press Ltd. TWO POLYMETHOXYFLAVONES FROM AGERATUM HOUSTONIANUM” L. QUIJANO, J. S. CALDER~N, F. G~)MEZ and T. Rios Instituto de Quimica, Universidad National Autonoma de Mexico, Circuit0 Exterior, Cd. Universitaria, Coyoacan, 04510 Mexico, D.F., Mexico (Revised received 21 April 1982) Key Word Index-Age&urn houstonianum; Asteraceae; Eupatorieae; new octasubstituted and heptasub- stituted flavones. Abstract-Besides agecorynin C, eupalestin and lucidin dimethyl ether, two new highly oxygenated flavones were isolated from Ageratum houstonianum. Their structures were established by spectroscopic and degrada- tive evidence as 5, 6, 7, 8, 2’, 3’, 4, S-octamethoxyflavone and 5, 6, 7, 2’, 3’, 4’, 5’-heptamethoxyflavone. INTRODUCTION In previous papers we have published the isolation and structure elucidation of several flavonoids from Ageratum corymbosum and A. strictum [l, 21. Now we report the results of our study of Ageratum hous- tonianum Mill. which resulted in the isolation of the already known lucidin dimethyl ether (2a) [3] eupalestin (2b) and agecorynin C (3) [l] as well as two new highly oxygenated flavones with a novel sub- stitution pattern in the B-ring, named agehoustin A (la) and B zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (lb). To our knowledge this is the first report of flavones with the 2’, 3’, 4’, 5’-oxygenation pattern and the second of flavones with a tetra-O- substituted B-ring [4]. Agehoustin A (la) is the first octamethoxyflavone from the Asteraceae and the third compound of this type yet reported from nature. Exoticin (3,5,6,7,8,3’,4’,5’-octamethoxyflavone) r51 and purpurascenin (3,5,6,7,8,2’,4’,5’- octamethoxyflavone) [6] are the other two octamethoxyflavonoids isolated so far. Some other octasubstituted flavonoids, with the same substitution pattern as exoticin have been also isolated [7]. RESULTS AND DISCUSSION The petrol extract of the aerial parts of Ageratum houstonianum afforded a mixture of several flavones. Three have been isolated before: lucidin dimethyl ether (2a) from Lindera lucida [3], eupalestin (2b) and agecorynin C (3) from Ageratum corymbosum [l]. In addition two new fully methylated and highly oxy- genated flavones, agehoustin A (la) and B zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC (lb), were isolated. Agehoustin A (la), Cz3Hz601,-,,was the less polar flavone isolated from the petrol extract, mp 116-l Is”. Both the UV (268, 318nm) and the IR (1636, 1580 cm-‘) absorptions were typical of non-phenolic flavones [8]. The ‘H NMR spectrum of la clearly *Part 3 in the series “Flavonoids from Ageratum Species”. For Part 2 see ref. [2]. This is contribution No. 604 of the Instituto de Quimica, U.N.A.M. indicated it to be an octasubstituted flavonoid, since it showed two singlets (1H each) at 6 6.88 and 7.13 indicating the presence of only two tlavone-nucleus protons. Six sharp singlets at 3.89 (3H), 3.91 (3H), 3.95 (9H), 3.98 (3H), 3.99 (3H), 4.09 (3H), indicated the presence of eight methoxy groups. The mass spectrum of agehoustin A (la) confirmed the assumption that it is an octamethoxyflavone, since the molecular ion peak was observed at m/z 462 and a base peak at 447 due to [M - Me]‘. Other spectral peaks at m/z 225 [A, -Me]‘, 197 [A, - Me-CO]+ due to A-ring fragmentation [9], suggested that, as in exoticin [5] and purpurascenin [6], agehoustin A (la) must have all A-ring positions substituted. Therefore the remain- ing four methoxyl groups can be placed on the B-ring since the ‘H NMR displayed two singlet flavone- nucleus protons. In addition, since the ‘H NMR spec- trum of la is different from that of purpurascenin (3, 5, 6, 7, 8, 2’, 4, 5’-octamethoxyflavone) [6], it must have the proposed structure la. Final confirmation of structure la was achieved by alkaline degradation which furnished 2-hydroxy-3, 4, 5, 6-tetramethoxy- acetophenone (4a) [l] and 2, 3, 4, 5-tetramethoxyben- zoic acid (5a) identified by its mp 82-84” [lo], IR, NMR and mass spectra. Hence agehoustin A is 5,6,7,8,2’, 3’, 4’, 5’-octamethoxyflavone (la). As in the case of agecorynin C (3) [l], additional degradation products were isolated and identified as the keto-enol 6a and 2, 3, 4, 5-tetramethoxyaceto- phenone (4b) and 2-hydroxy-3, 4, 5, 6-tetramethoxy- benzoic acid (5b). 4b and 5b can be explained as further degradation products of 6a (or its cor- responding P-diketone). A second new flavone, agehoustin B (lb), C2zHZ409, mp 85-86”, was isolated from the petrol extract. The ‘H NMR of lb was very similar to that of agecorynin C (3) [l]. It showed three singlets (1H each) at 6 6.70, 6.74 and 6.94 due to three flavone nucleus protons and five sharp singlets between 3.8 and 4.0 due to seven methoxy groups. Hence lb must be a new heptamethoxylated flavone whose structure can be 2965