Fungi live in competitive microbiomes which result in the production of biologically active secondary metabolites. These compounds are being investigated as new antibiotics for use in pharmacy and medicine. The isolation and characterization of these metabolites commonly includes extensive 1D and 2D NMR spectroscopic analysis. Current NMR studies of a metabolite isolated from Alternaria metachromatica only allowed for partial structure elucidation resulting in several substructures. Alteration of heteronuclear multiple bond correlation (HMBC) experimental parameters could allow for connection of these substructures by enhancing long-range JH-C correlations not normally seen in traditional experiments, possibly resulting in complete structure elucidation. The goal of this work is to study how altering HMBC parameters could enhance long-range carbon-hydrogen couplings in order to connect molecular substructures. To do this, the “long-range J value” experimental parameter was altered for a library of known compounds from the standard 8 Hz (displaying 2JH-C and 3JH-C correlations) to values such as 4 Hz, 2 Hz, and 1 Hz in an effort to amplify the 4JH-C and 5JH-C couplings. Compounds studied included ethyl acetate, ethylene glycol monomethyl ether acetate, cinnamaldehyde, p-anisaldehyde, citral, and 3,4-dimethoxycinnamic acid, all of which contain similar functional groups to the unknown compoundnatural product. the HMBC data of the known compounds showed enhanced 4 and 5 bond H-C correlations with smaller “long- range JJ values” such as 2 Hz and 1 Hz. This was especially true of compounds containing conjugated π systems and allowed for connection of substructures through ester functional groups. The 2 and 3 bond H-C correlations became weaker as the “long-range J value” approached 2 Hz. Trends in HMBC data for studied compounds related to functional group presence and long-range H-C correlations will be presented.

Alteration of HMBC parameters to show 4JH-C and 5JH-C correlations for the structural elucidation of a fungal secondary metabolite

253rd National Meeting (2017)

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