siphonodictyal-b1 and liphagal

The marine sponge Aka coralliphaga is a rich source of biologically active and structurally interesting meroterpenoids. Inspired by these natural products, we have used biosynthetic speculation to devise biomimetic syntheses of siphonodictyal B, liphagal and corallidictyals A-D from sclareolide. This work resulted in the development of new cascade reactions in the synthesis of liphagal, the reassignment of the structure of siphonodictyal B, and the realisation that corallidictyals A and B are possibly isolation artefacts.

Topics: Animals; Biological Products; Biomimetics; Cyclization; Diterpenes; Hydroquinones; Oxidation-Reduction; Porifera; Sesquiterpenes; Terpenes

An iodine-promoted sunlight-induced olefin Z/ E isomerization reaction together with a palladium-catalyzed direct cross-coupling reaction of a drimanal hydrazone and an iodobenzaldehyde, without touching the aromatic aldehyde group, facilitated a divergent and expeditious access to bioactive marine natural products siphonodictyal B, corallidictyals C/D, and liphagal based on the early presence of an aldehyde group instead of a late-stage introduction.

Topics: Aldehydes; Biological Products; Catalysis; Chemistry Techniques, Synthetic; Hydroquinones; Palladium; Sesquiterpenes; Stereoisomerism; Terpenes

The structure of siphonodictyal B has been reassigned on the basis of the total synthesis of both possible C-8 epimers. The revised structure of siphonodictyal B was converted into liphagal by acid catalyzed rearrangement of a proposed epoxide intermediate. This biomimetic cascade features a succession of four distinct reactions (epoxidation, o-quinone methide formation, ring expansion, and benzofuran formation) that occur in a one-pot operation under mild conditions. During these studies we also isolated a surprisingly stable o-quinone methide that supports our mechanistic proposal for liphagal biosynthesis.

Topics: Catalysis; Hydroquinones; Molecular Structure; Sesquiterpenes; Terpenes