Efficacy of Organophosphorus Derivatives Containing Chalcones/Chalcone Semicarbazones Against Fungal Pathogens of Sugarcane

Ten newly synthesized organophosphorus derivatives containing substituted chalcones and substituted chalcone semicarbazones were tested for their antifungal efficacy against Colletotrichum falcatum, Fusarium oxysporum, Curvularia pallescens (all sugarcane pathogens). The O,O-diethylphosphate derivatives containing 2-chlorochalcone and 2-chlorochalcone semicarbazone exhibited 70-85% mycelial inhibition against all the test fungi at 1000 ppm. The screening results were correlated with structural features of the tested compounds.


INTRODUCTION
Sugarcane is an important cash crop in many tropical and sub-tropical countries and is one of main sources of sugar production in the world. The crop is highly susceptible to various fungi, bacteria, viruses mycoplasma like organisms and other diseases due to which the yield is greatly reduced 2. Because of their economic importance sugarcane diseases have been studied in great depth from various angles3. Efficacy of Organophosphorusderivatives Containing Chalcones/ Chalcone Semicarbazones against Fungal Pathogens of Sugarcane A number of synthetic organic compounds viz., dithiocarbamates, carbamates, organochlorine, organomercuriale, thiocarbamates and hydrazides are now known to be useful in the control of various fungal diseases in plants45. Currently we are engaged 6"11 in synthesizing novel organophosphorus derivatives, which could constitute a new and promising field of application in the national economy. It was realized that on the basis of suitable logic, organic molecules incorporating phosphorus might be designed such that they may be less dangerous in use without losing thesis value as effective pesticides. The present study was therefore undertaken to evaluate the antifungal efficacy of some newly synthesized organophosphorus compounds against various important fungal pathogens of sugarcane. under inert atmosphere and anhydrous conditions. Special precaution were taken to exclude moisture from the apparatus and chemicals as the starting materials (O,O-diethylchlorophosphate) and reactions were susceptible to hydrolysis. Glass apparatus with interchangeable joints were used throughout the work. The solvents were purified and dried using the method described in the literature 2. O,O-diethylchlorophosphate was prepared according to the reported method 3. Chalcones/chalcone semicarbazones were prepared as described4. All reactions were carried out in the hood. A hood is a specially constructed workplace that has, at the least, a powered went to suck noxious fumes outside. The details of analysis and physical measurements were the same as reported earlier9.
For antifungal activity all the compounds were tested against all the test fungi by the food poison technique 5 at three concentrations (10, 100, 1000 ppm). For this the desired amount of chemical was dissolved in 0.5 cm of solvent and mixed with the culture medium on the basis of the volume of medium in each petriplate (80-ram diameter). Oat meal agar medium 6 was used for all test fungi. In controls, the same amount of medium containing the requisite amount of solvent was poured in place of test chemicals. A mycelial disk (5-ram diameter) obtained from the periphery of 2 week old cultures was taken and transferred to the center of each petriplate. Plates were incubated for 7 days at 28 +-2 o C. Each treatment was repeated three times and the inhibition was a recorded relative to percent mycelial inhibition calculated using the formula. [ where dC is the average diameter of the mycelial colony of the control and dT is the average diameter of the myceliai colony of the treatment.   5.42 (s) 6.50 (s)

Synthesis of Organophosphorus derivatives
The reactions of O,O-diethylchlorphosphate with semicarbazones of substituted chalcones derived by the condensation of 2-hydroxybenzalacetophenone benzal -2'-hydroxyacetophenone/2,2'dihydroxybenzalacetophenone/ 2-chlorobenzal 2-hydroxyacetophenone 3-methoxybenzal-2'hydroxyacetophenone and semicarbazide have been carried out in ethanol in the presence of pyridine and a variety of organophosphorus derivatives (types VI-X have been isolated according to Schemes 6 10. The analytical data and physical properties of all organophosphorus derivatives are given in Table-i. The methods used for the preparation and isolation of these compounds give materials of good purity as supported by their analysis and TLC. The spectral (IR, H NMR) data are given in Tables 2 and   3.

Anti fungai activity
Results of the antifungal assay of the organophosphorus derivatives are summarized in   The best activity was recorded with O,O-diethylchlorophosphate derivative containing 2chiorobenzal-2'-hydroxyacetophenone semicarbazone (IX). This compound showed activity upto 73.0% against C. falcatum_at 1000 ppm concentration.
Comparing the antifungal activity of different compounds can derive the following conclusions. (a) There were significant alteration in the antifungal activity with the change in the nature of organic group attached to O,O-diethylchlorophosphate moiety. (b) For any particular species of fungus, organophosphorus derivatives containing substituted chalcones were found to be more effective than its semicarbozone derivatives.
(c) For any particular series of organic compounds, the compounds containing chloro group in the chalcone ring show better activity. (d) The activity decreases of dilution.
There results indicate that studies on organophosphorus derivations could be promising as fungicides and constitute a new and promising field of application in disease and pest management.