Stereocontrolled Total Synthesis of Nonenolide

Nonenolide (1) was first isolated from the entomopathogenic fungus Cordyceps militaries BCC2816 and exhibited good antimalarial activity against Plasmodium falciparum K1. Structurally, it features a decanolide with a trans-double bond attached to two chiral hydroxy groups, making the total synthesis of the exclusive isomer of 1 more difficult. Herein, we report the successful synthesis of 1 by employing a MacMillan α-hydroxylation to generate three chiral centers in both the key fragments, starting from 1,6-hexanediol and 1,4-butanediol, followed by Steglich esterification of compounds 2 and 3. The exclusive E-isomer was obtained via a ring-closing metathesis of the mono-PMB-protected diene 19. Deprotection provided the required natural product 1.

Total synthesis of (+)-azaspiracid-1. An exhibition of the intricacies of complex molecule synthesis

The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.