Ningalin C is polar highly-colored alkaloid isolated in 1997 from dark purple Didemnum sp in Ningaloo Reef region at the northwest cape of Western Australia in the form of Dark-red amorphous powder.1
Reaction between 5-bromo-3methyl-2-pyrone and dimethoxy benzyne gave us synthetically useful naphthalene for natural product synthesis. With this naphthalene, we were able to synthesize key intermediates effectively. From those key intermediates, we recently had successfully synthesized ningalin D and G.2 Recently, we have further extended the above strategy and completed the synthesis of ningalin C. The key to the success was the assembly of the indole through the successive C-N coupling reactions. Functional group transformations, oxidations and necessary substituents allowed the synthesis of the title natural product, ningalin C.
1. Heonjoong Kang.; William Fenical. J. Org. Chem. 1997, 62, 3254.
2. Kim, J.-Y.; Kim, D.-H.; Jeon, T.-H.; Kim, W.-H.; Cho, C.-G. Org. Lett. 2017, 19, 4688.