Fungitoxic activity of two sequiterpene compounds from drechslera cynodontis against plant pathogen fungi

Two, sesquiterpenes; Dihydrobipolaroxin (1) and Sorokinianin (2). have been isolated from the culture filtrates of the fungus Drechslera cynodontis. This paper describes the isolation and structure elucidation of the two chemical compounds by EL-MS, 1H-NMR, 13C-NMR, DEPT, COSY, HMQC and HMBC spectra techniques that led to characterization of the two novel compounds; Dihydrobipolaroxin and Sorokinianin. The results obtained for identification of the compound 1 by EL-MS suggesting the molecular formula C18H2804. The structure showed consistent with the structure derived byl3C-NMR and DEPT spectrum and the structure was confirmed in full agreement with those reported for dihydrobipolaroxin sesquiterpene by Sugawara et al. 1985. The antifungal activity of culture filtrate of Drechslera isolate on the mycelial growth showed significant reduction in mycelial growth and spore germination of all plant pathogens under study. Data showed highly effective growth inhibition against A. solani, F. oxysporum and S. sclerotiorum up to 66.7%, while decreased the other fungal growth by 44.4-51.1% at concentration of 100 µg/ml. Compound 1 caused higher reduction in spore germination of A. solani (8%) and F. solani (77%) at 100 µg/ml concentration. For compound (2). The El-MS showed a molecular ion peak [M+1]+ at m/z 309 suggesting the molecular formula C18H2804. The detailed 1 H-NMR and 13C-NMR data were consistent and compound identified as Sorokinianin and in agreement with results reported by Nakajima et al. (1994). Compound 2 (Sorokinianin) decreased the fungal growth at concentration of 100 µg/ml in all tested fungi which ranged from 22.2% growth inhibition in R. solani to 61.1% in F. solani. Compound 2 was highly effective in suppressing spore germination of F. solani (75%) at 100µg/ml concentration. Data of experiments done to determine the minimum inhibitory concentrations (MIC) for fungal growth indicated that maximum concentration (100 µg/ml) of both compounds was not sufficient for inhibiting completely the growth of all tested fungi. All tested compounds recorded higher MIC values (100 µg/ml). The MIC for spore germination Compounds 1 and compounds 2 had less inhibitory effect on spore germination of all tested fungi, they recorded- higher MIC values (100 µg/ml).