Bioinspired total synthesis of boneratamides A-C.

We disclose the first synthesis of the marine natural product, (+)-boneratamide A, whose structure is composed of a terpene unit linked via an amide bond to a pyroglutamic acid moiety. The key step in this route is a bioinspired Ugi reaction of (+)-axisonitrile-3 with acetone as the carbonyl component and L-glutamic acid. This reaction brings about a remarkably efficient, one-pot assembly of reaction components concomitant with γ-lactam ring formation to produce (+)-boneratamide A in 70% yield. (+)-Boneratamide B and (-)-boneratamide C methyl esters were also synthesized using a similar bioinspired strategy, and the relative stereochemistries at the stereogenic centers in these substances were elucidated using X-ray analysis.

Total synthesis of exigurin: the Ugi reaction in a hypothetical biosynthesis of natural products.

The first total synthesis of a marine natural product, exigurin, has been accomplished in 13 steps starting from (+)-menthone. The key intermediate (-)-10-epi-axisonitrile-3 was prepared by stereoselective intramolecular cyclopropanation followed by a cyclopropane ring opening reaction by the azide anion. The bioinspired Ugi reaction of (-)-10-epi-axisonitrile-3, formaldehyde, sarcosine and methanol successfully constructed the target exigurin in which its terpene and amino acid units were linked through an amide bond.