Antiplasmodial and Larvicidal Flavonoids from the Seedpods of Tephrosia elata and Tephrosia aequilata

Abstract

The genus Tephrosia is rich in flavonoids and isoflavonoids including rotenoids. In the search for compounds with antiplasmodial and larvicidal activities from medicinal plants, the seedpods of Tephrosia elata and Tephrosia aequilata were analysed. The dried and ground seedpods of T. elata and T. aequilata were extracted separately with CH2Cl2/MeOH (1:1) by cold percolation for 24 hours at room temperature. The crude extracts showed significant antiplasmodial activities with IC50 values of 8.4 + 0.3 and 8.6 + 1.0 g/ml for T. elata, and 1.5 + 0.2 g/ml and 22.4 + 5.2 g/ml for T. aequilata, against chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum, respectively. The crude seedpods extract of T. elata also showed larvicidal activity against the mosquito larvae of Aedes aegypti with LC50 of 68.9 ± 0.3 g/ml at 24 hours and 40.2 ± 0.2 g/ml at 48 hours. Chromatographic separation of the CH2Cl2/MeOH (1:1) extract of the seedpods of T. elata led to the isolation of seven compounds. These were identified as the β-hydroxydihydrochalcone (S)-(-)-3',4'-(2'',2''-dimethylpyrano)-2',-dihydroxy-6'-methoxydihydrochalcone, trivial name elatadihydrochalcone (1); the chalcone obovatachalcone (3); the flavanones, obovatin (4) and obovatin methyl ether (5); the rotenoids deguelin (6) and rotenone (7). The CH2Cl2/MeOH (1:1) crude seedpods extract of T. aequilata yielded three known compounds, obovatin methyl ether (5), (E)-praecansone A (8) and demethylpraecansone B (9). Elatadihydrochalcone (1) is a novel compound and is the first of its kind in the genus Tephrosia. The presence of β-hydroxy group was confirmed by the preparation of the mono acetate, -acetoxyelatadihtydrochalcone (2). Obovatachalcone (3), obovatin (4), deguelin (6) and rotenone (7) are reported here for the first time from T. elata. The identification of these compounds was based on spectroscopic techniques (1H NMR, 13C NMR, HMBC, HMQC, COSY, DEPT, nOe, UV and MS). The stereochemistry in elatadihydrochalcone (1) was determined from CD spectrum. The isolated compounds from T. elata were tested for antiplasmodial activities. The novel compound, elatadihydrochalcone (1) showed antiplasmodial activity with IC50 = 2.8 + 0.3 g/ml and 5.5 + 0.3 g/ml against (D6) and (W2), respectively. Obovatin methyl ether (5) showed activity against (D6) and (W2) strains of P. falciparum with IC50 value of 3.8 + 0.3 and 4.4 + 0.6 g/ml, respectively. Praecansone A (8) showed antiplasmodial activity with IC50 value of 6.6 + 1.1 g/ml and 6.4 + 1.0 g/ml against D6 and W2 respectively. Deguelin (6) and rotenone (7) together showed larvicidal activity against 3rd instar mosquito larvae of Aedes aegypti with LC50 value of 7.6 ± 0.4 g/ml at 24 hours.