Natural Products Chemistry of Ischnoderma resinosum (P. Karst)

Ischnoderma resinosum (P. Karst), commonly known as the late-fall polypore, is an edible mushroom that belongs to the order, Polyporales, family Ischnodermataceae. The shelf-like fungus grows in the early to late fall and is widely distributed in North American hard wood forests. Ischnoderma resinosum is consumed when young and tender and has a history of purported medicinal properties. Because of its use by indigenous peoples and pleasant odor profile, I. resinosum was chosen as a promising candidate for use in food, flavor and potential pharmaceutical applications. Accordingly, this project was designed to: 1) identify the key odorants contributing to the “candy-like” odor of the fungus, 2) elucidate the biosynthetic pathway for benzylic derivative production, 3) characterize the fermentation dynamics and the benzylic derivative production among different I. resinosum genotypes, and 4) isolate and elucidate the structure of antimicrobial natural products present in the fungus. Eighteen odorants were identified from 16-day old fermentations. Odor activity values revealed 4-methoxybenzaldehyde (4-MBA; anise), 3,4-dimethoxybenzaldehyde (3,4-DMBA; vanilla), and benzaldehyde (BA; cherry) as key contributors to the pleasant “candy-like” odor. The biosynthetic pathway leading to a series of benzylic derivatives including BA, 4-MBA and 3,4-DMBA was elucidated employing isotope incubation studies. A putative metabolic scheme for biosynthesis of benzylic derivatives in I. resinosum fermentations was proposed. Variations in fermentation dynamics including D-glucose, D-fructose, ethanol, L-lactic acid, acetic acid, and pH along with benzylic derivative production were evaluated in fermentations of different I. resinosum genotypes over 30 days. Genotype I3 was the highest producer of BA and 4-MBA, whereas genotype I4 was the highest producer of 3,4-DMBA. Furthermore, activity-guided fractionation of I. resinosum extracts coupled with analytical methods including liquid chromatography-mass spectrometry (LC-MS), high-resolution mass spectrometry (HRMS), nuclear magnetic resonance (NMR), and Fourier-transform infrared spectroscopy (FTIR) led to the isolation and structural elucidation of novel 1-(4-methoxyphenyl)-1-oxopropan-2-yl sulfate with antibacterial activity against gram negative and positive bacteria. As the first comprehensive characterization of both volatile and non-volatile compound repertoire of I. resinosum, this study lays the groundwork for future investigations aimed at evaluating the fungus’s potential use in food, flavor and pharmacological applications.

Portions of this document were previously published in journal of Agricultural Food Chemistry.