Oxirapentyn

Chemical investigations of two fungal isolates initially identified as members of the genus Phialemonium are described. Both isolates were obtained as colonists of other fungi collected on the island of Hawaii and were later assigned as P. curvatum. However, P. curvatum has recently been reclassified as a member of a new genus (Phialemoniopsis) and renamed as Phialemoniopsis curvata. Studies of solid-substrate fermentation cultures of one of these isolates afforded an oxirapentyn analogue and destruxin A4 as major components, while analysis of the second strain led to the isolation of several simple aromatic metabolites and a compound of mixed biogenetic origin called gabusectin that had previously been reported only in a patent. Structures were assigned mainly by detailed nuclear magnetic resonance and mass spectrometry analysis, and those of two of the major components were confirmed by X-ray crystallography. This report constitutes the first description of secondary metabolites from a member of the genus Phialemoniopsis.

Six new highly oxygenated chromene derivatives, oxirapentyns F-K (2-7), one new polyketide (8), one new benzofurane (9), and two known cyclodepsipeptides, isoisariin B and isaridin E, were isolated from the lipophilic extract of the marine-derived fungus Isaria felina KMM 4639. The structures of compounds 2-9 were determined using spectroscopic methods. The relative configurations of compounds 2-7 were established through a combination of NOE data and spin coupling constants, and these results were confirmed by X-ray crystallographic analysis of 4. The absolute structures of all oxirapentyns were assumed based on their biogenetic relationship and confirmed using the modified Mosher's method on 2 and 7. Isariketide (8) showed moderate cytotoxicity toward HL-60 cells.

Oxirapentyn A (1), oxirapentyn B (2), and oxirapentyn E (3) were examined for their ability to stimulate growth of seedling roots of barley (Hordeum vulgare L.), buckwheat (Fagopyrum esculentum Moench), corn (Zea mays L.), soy {Glycine max (L.) Merr.}, and wheat (Triticum aestivum L.). It was shown that the stimulatory effects depend on the chemical structure of the oxirapentyns and on the plant species. Compounds 1, and 2 are efficient for growth of seedling roots of barley, and wheat, whereas compound 3, at different concentrations, stimulates growth of seedling roots of maize, soy, and wheat. These compounds can be recommended for field study as plant growth stimulators.