Total Synthesis of the Proposed Structure of (−)-Novofumigatamide, Isomers Thereof, and Analogues. Part I

The total synthesis of the suggested structure of (−)-novofumigatamide, a natural product containing a C3-reverse prenylated N-acetyl-exo-hexahydropyrrolo­[2,3-b]­indole motif fused to a 10-membered ring lactam, was achieved using the macrolactam formation in advance of a diastereoselective bromocyclization and reverse prenylation steps. Since the NMR data of the synthetic sample did not match those of the natural product, the endo-bromo precursor of a N-Boc analogue and additional diastereomers derived from l-Trp were also synthesized. Five alternative synthetic routes, which differed in the order of final key steps used for the construction of the 10-membered ring lactam and the hexahydropyrrolo­[2,3-b]­indole framework within the polycyclic skeleton and also in the amide bond selected for the ring-closing of the macrolactam, were thoroughly explored. Much to our dismay, the lack of spectroscopic correlations between the proposed structure of natural (−)-novofumigatamide and the synthetic products suggested a different connectivity between the atoms. Additional synthetic efforts to assemble alternative structures of the natural product and isomers thereof (see accompanying paper; DOI: 10.1021/acs.joc.2c01228) further highlighted the frustrating endeavors toward the identification of a natural product.