At 0.1 mg/mL, the ethyl acetate extract (EAE) of the crude 85% methanolic extract (CAE) of Stevia rebaudiana leaves exhibited preventive activity against DNA strand scission by *OH generated in Fenton's reaction on pBluescript II SK (-) DNA. Its efficacy is better than that of quercetin. The radical scavenging capacity of CAE was evaluated by the DPPH test (IC50=47.66+/-1.04 microg/mL). EAE was derived from CAE scavenged DPPH (IC50=9.26+/-0.04 microg/mL), ABTS+ (IC50=3.04+/-0.22 microg/mL) and *OH (IC50=3.08+/-0.19 microg/mL). Additionally, inhibition of lipid peroxidation induced with 25 mM FeSO 4 on rat liver homogenate as a lipid source was noted with CAE (IC50=2.1+/-1.07 mg/mL). The total polyphenols and total flavonoids of EAE were 0.86 mg gallic acid equivalents/mg and 0.83 mg of quercetin equivalents/mg, respectively. Flavonoids, isolated from EAE, were characterized as quercetin-3-O-arabinoside, quercitrin, apigenin, apigenin-4-O-glucoside, luteolin, and kaempferol-3-O-rhamnoside by LC-MS and NMR analysis. These results indicate that Stevia rebaudiana may be useful as a potential source of natural antioxidants.

Prompted by our discovery of a new class of conformationally-locked indeno[2,1-c]quinolines as anti-mycobacterials, compounds 2a and 3a (Fig. 1; MIC < 0.39 μg mL(-1) and 0.78 μg mL(-1), respectively)(14) with a freely rotating C2-imidazolo substituent, we herein describe the synthesis of pentacyclic azole-fused quinoline derivatives 4 and 5, in which we have restricted the rotation of the C2-imidazolo moiety by fusing it to the adjacent quinoline-nitrogen to give a five-membered fused azole heterocycle. The idea of locking the flexibility of the system by conformational constraint was simply to reduce its entropy, thereby reducing the overall free-energy of its binding to the target receptor. Out of 22 different azole-fused indeno[2,1-c]quinoline derivatives, seven structurally distinct compounds, 9, 15, 17, 25, 27, 28 and 29, have shown 79-99% growth inhibition of Mycobacterium tuberculosis H37Rv at a fixed dose of 6.25 μg mL(-1). The efficacies of these compounds were evaluated in vitro for 8/9 consecutive days using the BACTEC radiometric assay upon administration of single dose on day one. Of these, two compounds, 9 and 28, inhibited growth of M. tuberculosis very effectively at MIC < 0.39 μg mL(-1) (0.89 μM and 1 μM, respectively). These active compounds 9, 15, 17, 25, 27, 28 and 29 were screened for their cytotoxic effect on mammalian cells (human monocytic cell line U937), which showed that the human cell survival is almost unperturbed (100% survival), except for compound 25, hence these new compounds with new scaffolds have been identified as potent anti-mycobacterials, virtually with no toxicity. Thus these "hit" molecules constitute our important "leads" for further optimization by structure-activity relationship against TB.

Bioactivity-guided fractionation has led to the successful isolation of calceolarioside A ( 1) from the methanolic extract of night jasmine leaves. The in vitro antileishmanial activity of compound 1 was determined (IC (50) = 20 microg/mL). Its IN VIVO efficacy was noted at 20 mg/kg body weight when it reduced the hepatic and splenic parasite burden by 79 and 84 %, respectively, in an established model of L. donovani Ag83 infected golden hamster. Furthermore, synergistic potentiations of compound 1 at 20 mg/kg body weight and SAG at 5 mg/kg body weight showed a significant reduction of hepatic and splenic parasite burden. No cytotoxicity was observed against the U937 cell line. This is the first report describing the isolation of compound 1 from N. arbor-tristis L. and the first demonstration of its potent activity against visceral leishmaniasis.