Ambuic acid, a highly functionalized cyclohexenone with antifungal activity from Pestalotiopsis spp. and Monochaetia sp.
Introduction
Pestalotiopsis spp. and Monochaetia sp. (a related fungal genus) are generally found as endophytic fungi of rainforest plants. However, the former fungus appears more frequently than the latter. One of the most common Pestalotiopsis sp. that does occur as an endophyte is P. microspora. Organisms virtually identical to the taxonomic description of P. microspora are numerous. These fungi have usually been isolated as leaf and stem pathogens of economically important tropical plants such as the palms, pines, loquats, guavas, mangoes and a large number of ornamental plants (Raj, 1993). Generally, this fungus is viewed as a relatively weak plant pathogen, but at times it may act in a more severe manner and cause major plant loss. Most often, however, no signs or symptoms of these fungi are to be found by an external examination of the plant. Culturing of the inner tissues of surface sterilized stems, petioles or leaves of plants commonly will yield pure cultures of P. microspora (or related fungi).
Furthermore, besides being widespread, another feature of Pestalotiopsis spp. is its wide genetic and biological diversity (Li et al., 1996). We have other indications that enormous variability must exist in this organism arising by mutation, genetic crossing, or by as yet undiscovered mechanisms such as genetic exchange with its hosts. It also appears that P. microspora is a microbial factory of bioactive secondary metabolites and these compounds may contribute to the biological interactions occurring between the fungus and its plant host.
Thus, this report describes a novel organic acid, ambuic acid, that is present in isolates of Pestalotiopsis spp. and a Monochaetia sp. obtained as endophytes from several of the major representative rainforests of the world. It structure has been determined by NMR and mass spectroscopic methods and some of its biological activities examined.
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Results and discussion
Pestalotiopsis spp. and Monochaetia sp., the fungal endophytes, were isolated from the inner tissues of surface- sterilized plant materials including leaves, stems and petioles. The plant materials were collected in rainforests of several countries. The fungi were obtained as pure colonies by picking and culturing hyphal tips as they grew from the plant materials (Strobel et al., 1996). The fungi were identified on the basis of the structure of the asexual fruiting bodies (acervuli) and conidia
General spectroscopic precedures
A 2D INADEQUATE analysis was performed on a 21 mg sample dissolved in 30 μl of d4-methanol. Acquisition was performed using a Varian INOVA 500 MHz spectrometer operating at 125.894 MHz equipped with a Varian nanoprobe (Barbara, 1994). A sample spinning speed of 2000 Hz was used for analysis. Subsequent collection of additional ambuic acid provided for a second 2D INADEQUATE analysis on 131 mg in 0.7 ml d6-DMSO to establish three 13C-13C bonds missing (C5–C10, C9–C10, and C8–C19) from the
Acknowledgments
The authors thank Dr. Joe Sears for acquiring mass spectral data. We also wish to thank Dr. Scott Busse for assistance in acquiring NOE difference data. This work was supported by the National Institute of Health of the Department of Health and Human Services under Grant GM08521-38 and by the Montana Agricultural Experiment Station, Brigham Young University, and Cytoclonal Pharmaceutics of Dallas, Texas. Atlantic Microlab of Norcross, Ga. performed the elemental analyses. The help of several
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