Isolation and Identification of Fungistatic Compounds from Seeds of Guettarda poasana

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Dr. K. Gregory Murray, Hope College
Dr. Michael Short, Hope College

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Despite formidable pressure from rodents, arthropods, and microbes, the seeds of many tropical plants are able to remain dormant and viable in the soil for tens to hundreds of years. This is especially true of many pioneer species such as Guettarda poasana (Rubiaceae). Pioneer plants are fast-growing, shade-intolerant species that specialize on early successional patches and therefore play an important role in forest regeneration. For many species of pioneers, protection against animals and microbes seems to be conferred by toxic chemicals in the seeds. At Monteverde, Costa Rica, G. poasana seeds have been shown to accumulate to high densities (> 100/m2) in the soil, suggesting strong chemical defense. We used several extraction and identification procedures, guided by poisoned-medium bioassays, to isolate and identify anti-fungal compounds responsible for persistence of G. poasana seeds in the soil. Crude extracts from G. poasana seeds are highly toxic to fungi, and we have isolated ca. nineteen compounds of interest from the toxic fractions using preparative TLC. The first compound successfully isolated and identified was not highly toxic, but ongoing work in our lab promises to identify the toxic individual compounds as we further purify them and are able to obtain NMR spectra. Although our primary goal is to understand the chemical basis for pioneer seed persistence in the soil, some of the compounds responsible may also have pharmaceutical potential.

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