Homojesterones: vinylogous analogues of jesterone from Helminthosporium velutinum TS28

trans- and cis-Homojesterone (1 and 2, respectively), vinylogous analogs of jesterone, were isolated from Helminthosporium velutinum TS28. The relative configurational relationship between H-6 and H-7 was determined by comparing their 3JH-6/H-7 values with those of jesterones in literature, as well as with structurally related natural products. The relative configurations were confirmed by a remarkable magnetic shielding of the C1-methyl protons upon naphthoylation of 1. The naphthoylation also enabled us to determine the absolute configurations of 1 and 2 by a combination of conformational analyses and application of ECD exciton coupling theory.

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