Phytotoxic furanocoumarins from the shoots of Semenovia transiliensis.

Discovery of novel, natural herbicides has become important to manage increasing weed resistance to synthetic herbicides and environmental issues. The systematic bioassay-guided fractionation and purification of the methylene chloride/methanol extract of the shoots of Semenovia transiliensis led to the isolation of several phytotoxic compounds. Lactuca sativa L. (lettuce, a dicot) and Agrostis stolonifera L. (bentgrass, a monocot) bioassays were used to identify and isolate the phytotoxic fractions. A number of furanocoumarin compounds isolated from S. transiliensis shoots were phytotoxic to both test species. These included psoralen, isopsoralen, heratomin, isopentenyloxyisobergapten, imperatorin, bergapten, xanthotoxin, heraclenin, and heraclenol. All the active secondary metabolites isolated from the shoots of S. transiliensis were furanocoumarins. Identification of these was accomplished using mass spectrometry and 1- and 2-dimensional NMR techniques. Phytotoxic activity o f isolated compounds w a s evaluated in a dose-response manner from 0.3 to 1000 microM. Ingeneral, all of the compounds were more active on A. stolonifera than L. sativa. Bergaptin and xanthotoxin were the most active of the compounds, with moderate activity at 100 microM. Imperatorin and xanthotoxin inhibited growth of Lemna paucicostata Hegelm. by 50% at 29 and 60 microM, respectively. Our results show that S. transiliensis is rich in furanocoumarins, which are probably involved in various aspects of the chemical ecology of the species. Unfortunately, the general cytotoxicity of furanocoumarins makes them an unlikely candidate for pesticide discovery.

Structure-activity relationship studies on the mosquito toxicity and biting deterrency of callicarpenal derivatives.

Callicarpenal (=13,14,15,16-tetranorclerod-3-en-12-al=[(1S,2R,4aR,8aR)-1,2,3,4,4a,7,8,8a-octahydro-1,2,4a,5-tetramethylnaphthalen-1-yl]acetaldehyde; 1) has previously demonstrated significant mosquito bite-deterring activity against Aedes aegypti and Anopheles stephensi in addition to repellent activity against host-seeking nymphs of the blacklegged tick, Ixodes scapularis. In the present study, structural modifications were performed on callicarpenal (1) in an effort to understand the functional groups necessary for maintaining and/or increasing its activity and to possibly lead to more effective insect control agents. All modifications in this study targeted the C(12) aldehyde or the C(3) alkene functionalities or combinations thereof. Mosquito biting deterrency appeared to be influenced most by C(3) alkene modification as evidenced by catalytic hydrogenation that resulted in a compound having significantly less effectiveness than 1 at a test amount of 25 nmol/cm2. Oxidation and/or reduction of the C(12) aldehyde did not diminish mosquito biting deterrency, but, at the same time, none of the modifications were more effective than 1 in deterring mosquito biting. Toxicities of synthesized compounds towards Ae. aegypti ranged from an LD50 value of 2.36 to 40.11 microg per mosquito. Similarly, LD95 values ranged from a low of 5.59 to a high of 104.9 microg.