Bioinspired Syntheses of Herqulines B and C from Cyclodipeptide Mycocyclosin

A bioinspired approach for the syntheses of herqulines B and C is reported that takes advantage of an Ltyrosine-derived diketopiperazine, a mycocyclosin analog, as a synthetic precursor. The strategy relies on a series of consecutive reductions to adjust the mycocyclosin oxidation state to that observed in the herquline class of natural products. The strained and distorted L-tyrosine-based biaryl system characteristic for mycocyclosin is selectively converted to the 1,4-diketone structural motif common to the herqulines via initial hypervalent iodine-mediated dearomatization and a subsequent directed Birch reduction, enabled by an intramolecular H-source. The piperazine oxidation state is accessible in an iron-catalyzed reduction of the diketopiperazine precursor.