Divergent Asymmetric Synthesis of Panowamycins, TM-135, and Veramycin F Using C-H Insertion with Donor/Donor Carbenes

Panowamycins are a group of isochroman-based natural products first isolated from Streptomyces sp. K07-0010 in 2012 by Satoshi Omura and co-workers that exhibit modest anti-trypanosomal activity. Herein we demonstrate the first syntheses of these natural products and their epimers. Stereoselective dirhodium-catalyzed C-H insertion reactions with a donor/donor carbene construct the substituted isochroman core in the key bond-forming step. The syntheses are completed without the use of protecting groups and feature a late-stage Wacker oxidation. Incongruent NMR spectra between natural and synthetic samples revealed the structural misassignment of panowamycin A and veramycin F. Computational NMR studies suggested panowamycin A to be an alternate diastereomer, which was confirmed by synthesizing this isomer. Concurrent with this work, in 2021 Mahmud and co-workers came to the same conclusion with an updated NMR analysis of panowamycin A. In a divergent, asymmetric sequence, we report the synthesis of panowamycin A, panowamycin B, TM-135, and veramycin F.