Indian Journal of Chemistry Vol. 47B December 2008, pp. 1898-1902 Chemical constituents of Limnophila indica G Brahmachari*, S K Jash, A Gangopadhyay, S Sarkar, S Laskar & D Gorai Natural Products Laboratory, Department of Chemistry, Visva-Bharati University, Santiniketan 731 235, India E-mail: brahmg2001@yahoo.co.in Received 19 June 2008; accepted (revised) 12 September 2008 Two flavonoids, 5,6-dihydroxy-7,8,4'-trimethoxy flavone 1 and 5,2'-dihydroxy-8,3',4'-trimethoxyflavone 2 together with three known compounds, 5-hydroxy-7,2'-dimethoxyflavone 3, 5,2'-dihydroxy-7,8-dimethoxyflavone 4 and β-sitosterol 5, have been isolated from the aerial parts and roots of Limnophila indica (Scrophulariaceae). The structures of compounds 1-5 have been elucidated on the basis of spectral and chemical studies. Keywords: Chelated, unsaturated, Limnophila indica, flavone, flavonoids Limnophila indica (Linn.) Druce (Scrophulariaceae) 1,2 is a small aquatic herb, used widely in traditional Indian medicine in the treatment of various diseases like pestilent fever, dysentery, and elephantiasis 3-5 ; the plant has also been reported to possess immense anti-microbial activity 6 . In continuation to our previous works on this plant 7-9 , we herein report the isolation and structural elucidation of two novel flavonoids, 5,6-dihydroxy-7,8,4'- trimethoxyflavone 1 and 5,2'-dihydroxy-8,3',4'- trimethoxyflavone 2, together with three known compounds, 5-hydroxy-7,2'-dimethoxyflavone 3, 5,2'- dihydroxy-7,8-dimethoxyflavone 4 and β-sitosterol 5, from the aerial parts and roots of L. indica. The structures of compounds 1-5 were elucidated on the basis of spectral and chemical studies. O O R 1 R 2 R 3 R 4 R 5 R 6 R 7 1: R 1 = R 2 =OH; R 3 = R 4 = R 7 = OCH 3 ; R 5 = R 6 = H 2: R 1 = R 5 =OH; R 4 = R 6 = R 7 = OCH 3 ; R 2 = R 3 = H 1a: R 1 = R 2 = R 3 = R 4 = R 7 = OCH 3 ; R 5 = R 6 = H O O OH R 1 R 2 R 3 4: R 1 = R 2 = OCH 3 ; R 3 = OH 3: R 1 = R 3 = OCH 3 ; R 2 = H O H 5 Results and Discussion The compound 1, C 18 H 16 O 7 ([M] + at m/z 344), responded positively towards Shinoda test 10 and an alcoholic solution of the compound imparted an intense green colour with ferric chloride solution, indicating thereby that 1 is a flavonoid derivative with a free hydroxyl at C 5 -position 11 . Its UV spectrum gave the absorption bands at λ max 282 and 329 nm, suggestive of a flavone derivative unsubstituted at 3-position 12,13 . IR spectrum of 1 showed characteristic absorption bands for the presence of bonded hydroxyl function (3411 cm -1 ), chelated α,β-unsaturated carbonyl attached with aromatic nucleus (1661, 1590, 1507.5, 1388 cm -1 ), and methoxy group(s) (2939, 2842, 1266, 1025 cm -1 ) into the molecule; presence of three methoxyl functions in the molecule was also supported from the results of functional group analysis (Zeisel estimation) as well as from the results of other spectroscopic experiments. The 1 H NMR spectrum of 1 displayed signals at (i) δ 12.78 (1H, s) due to a strongly hydrogen-bonded phenolic hydroxyl function (D 2 O exchangeable); (ii) δ 6.58 (1H, s) attributed to C 3 -H; (iii) δ 6.44 (1H, s) due to a free phenolic hydroxyl group (D 2 O exchangeable) (iv) δ 4.04 (3H, s), 4.02 (3H,s), 3.90 (3H,s) for three methoxyl functions; (v) δ 7.89 (2H, d, J = 9Hz, H-2' and H-6') and (vii) δ 7.04 (2H, d, J = 9Hz, H-3' & H-5'). The characteristic mass spectral