The configuration about the C-2=C-8 double bond for the major isomer of the natural product ethylidene-4,6-dimethoxycoumaran-3-one isolated from the shrub Pogostemon quadrifolius (Benth.) was consistently determined to be Z by the examination of long-range NOE contacts (eta(S)(H,H)), chemical shifts (delta(s)(C)), and scalar coupling constants ((3)J(H8.H9), (1)J(H8), (3)J(H8,c3), and (2)J(H8,c2)) in conjunction with DFT calculations. The Js was found to be very amenable to the structural analysis and disparate in terms of their magnitude, and in the case of (2)J(H8,c2), by the sign.
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Journal article published