Microwave assisted solvent-free synthesis and biological activities of novel imines (Schiff bases).

Twelve new ortho-Hydroxyketimines were synthesized by conventional as well as microwave method and evaluated for their antinemic activity against Meloidogyne incognita [(Kofoid and White) Chitwood]. Conventional methods for synthesis of Schiff bases require refluxing at 140 degrees C of the reactants in different solvents for at least 24 h or more, where as the microwave-assisted synthesis has brought down the reaction time from 24 h to 1 minute. The procedure reported is simple as it does not require any organic solvents and the time has been reduced to only 1 minute. Comparative yields of all compounds by different methods revealed that the yield was low in conventional method (79-87%) as compared to microwave assisted synthesis (94-97%). The bioassay revealed that all the test compounds exhibited promising nematicidal activity; N-propyl-2-hydroxypropiophenonimine being the most effective with LC(50) value of 74.46 mgL(-1) followed by N-hexyl-2-hydroxyacetophenonimine with LC(50) value of 99.60 mgL(-1) after 72 h of exposure. The results obtained from bioassay indicated that this class of compounds has not only given a lead with regard to potential of Schiff bases in pest control, but has suggested that a carbon chain length of 6 atoms in the side chain is optimum on the basis of structure activity relationship (SAR).

Assessment of phytotoxicity of parthenin.

Phytotoxicity of parthenin, a sesquiterpene lactone, was evaluated against four weedy species (Amaranthus viridis, Cassia occidentalis, Echinochloa crus-galli, and Phalaris minor) through a series of experiments conducted under laboratory or greenhouse conditions to assess its herbicidal potential. Under laboratory conditions, parthenin (0.5-2 mM) severely reduced seedling growth (root and shoot) and dry weight of test weeds. However, the effect was greater on root growth. Parthenin (1 mM) suppressed the mitotic activity in the onion root tip cells that could possibly be responsible for the reduction in seedling growth. Both pre- and post-emergent application of parthenin caused a significant loss of chlorophyll pigments and affected photosynthesis. Parthenin ( > or =1 mM) caused an excessive electrolyte leakage in the plant tissues which was light-dependent. The root inhibition was associated with swelling and blackening of the root tip, shriveling and damage to the epidermal tissue and non-formation of root hairs. The study concludes that parthenin possesses weed-suppressing potential (both pre- and post-).

Effect of parthenin--a sesquiterpene lactone from Parthenium hysterophorus--on early growth and physiology of Ageratum conyzoides.

A study was undertaken to assess the effect of parthenin--a sesquiterpene lactone from Parthenium hysterophorus--on the germination, growth, and some associated physiological changes in Ageratum conyzoides. The study reveals that germination and growth of A. conyzoides was severely reduced by parthenin in the concentration range of 50, 100, and 200 microM, while at 400 microM a complete inhibition of germination was observed. The radicle length of A. conyzoides was reduced more than the plumule length. Further, the content of the photosynthetic pigment chlorophyll was appreciably reduced in the leaves of test plants spray treated with parthenin at 200 microM concentration. However, this inhibitory effect declined with the passage of time and at 10 days after treatment only a 25% reduction in chlorophyll content was observed compared to 76% on the first day after spray. Likewise, the cellular respiration measured through 2,3,5-triphenyl tetrazolium chloride was found to be less in the treated leaves, and the inhibitory response also declined with time. The content of proteins and carbohydrates decreased with the passage of time after parthenin treatment. The specific activities of the enzymes protease and alpha- and beta-amylase were also adversely affected in the parthenin treated leaves. In the case of protease. the activity decreased with passage of time while those of the amylases increased. Thus, we conclude that parthenin affects the germination and growth of A. conyzoides by altering the contents of some macromolecules and the specific activities of some enzymes. Such observations may be helpful in further exploring parthenin's mode of action.