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Modern drug discovery efforts rely, to a large extent, on lead compounds from two classes of small organic molecules; namely, natural products (i.e., secondary metabolites) and designed compounds (i.e., synthetic molecules). In this article, we demonstrate how these two domains of lead compounds can be merged through total synthesis and molecular design of analogs patterned after the targeted natural products, whose promising biological properties provide the motivation. Specifically, the present study targeted the naturally occurring biyouyanagins A and B and their analogs through modular chemical synthesis and led to the discovery of small organic molecules possessing anti-HIV and anti-arenavirus properties.

Syntheses of the three key building blocks (65, 98, and 100) required for the total synthesis of the proposed structure of azaspiracid-1 (1a) are described. Key steps include a TMSOTf-induced ring-closing cascade to form the ABC rings of tetracycle 65, a neodymium-catalyzed internal aminal formation for the construction of intermediate 98, and a Nozaki-Hiyama-Kishi coupling to assemble the required carbon chain of fragment 100. The synthesized fragments, obtained stereoselectively in both their enantiomeric forms, were expected to allow for the construction of all four stereoisomers proposed as possible structures of azaspiracid-1 (1a-d), thus allowing the determination of both the relative and absolute stereochemistry of the natural product.