Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Nikolaus H. Fischer

Abstract

The first part of this work was conducted to search for allelochemicals from the rice varieties PI346833 (moderately resistant) and Mars (susceptible) that may be responsible for resistance to fall armyworm, Spodoptera frugiperda (J. E. Smith) feeding. Mature tillers and seedlings were extracted with petroleum ether (PE), dichloromethane (DCM), acetone, methanol and water. The search for biological activity towards fall armyworm (FAW) was directed by growth inhibition bioassay. Significant antibiotic activity to FAW was observed with the PE and DCM crude extracts. Bioassay of the fractions of the PE and DCM extracts indicated that the fractions from PI346833 seedlings adversely affected the development of FAW, mainly by blocking pupation. Purification of one of the active fractions (PE-4) led to the isolation of the sitosterols $\beta$-sitosterol, stigmasterol and campesterol and, the triterpene isoarborinol. Dose-response bioassays with authentic stigmasterol and a sitosterol mixture adversely affected the development of FAW but did not show a positive correlation between dose and antibiosis. Volatile compounds of the rice seedlings were collected by dynamic headspace sampling and trapping on Tenax TA. Thermal desorption and cryogenic focusing were used to introduce the volatile compounds to the column for analysis by gas chromatography-mass spectrometry. Among the compounds detected, twenty-eight compounds were identified. Mars contained numerous and greater quantities of volatile compounds compared to PI346833. Twelve compounds were found only in Mars and two were found only in PI346833. The second part of this research dealt with the isolation and identification of the major external flavonoids from leaves of Calamintha ashei (Lamiaceae). A new flavone, 5,6,4$\sp\prime$-trihydroxy-7,8,3$\sp\prime$-trimethoxyflavone (1), a new natural aglycone, 5,6,4$\sp\prime$-trihydroxy-7,3$\sp\prime$-dimethoxyflavone (2), 5,4$\sp\prime$-dihydroxy-6,7,8,3$\sp\prime$-tetramethoxyflavone (3) and 5-hydroxy-6,7,8,3$\sp\prime$,4$\sp\prime$-pentamethoxyflavone (4) were identified by spectroscopic methods. The NMR method INAPT (Insensitive Nuclei Assigned by Polarization Transfer) was used and demonstrated as a new general method of solving problems in flavonoid structure determination. INAPT was found to be a sensitive and selective method of distinguishing among 5,6,7-, 5,7,8-substituted flavonol/flavone and 5,6,7,8-substituted flavone.

Pages

149

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