Some chemical speculation on the biosynthesis of corallidictyals A-D

The efficient conversion of siphonodictyal B into the spirocyclic natural products corallidictyals A-D has been achieved via oxidative and acid catalyzed cyclizations. The oxidative cyclization of siphonodictyal B occured spontaneously under aerobic oxidation conditions, which suggests that corallidictyals A and B are possibly artefacts of the isolation process. The mechanism of the oxidative cyclization of siphonodictyal B could be described as either an anionic 5-endo-trig cyclization (which is formally disfavoured by Baldwin's rules), or as an electrocyclic reaction, of an ortho-quinone intermediate.Adrian W. Markwell-Heys and Jonathan H. Georg

Total synthesis and structure revision of (-)-siphonodictyal B and its biomimetic conversion into (+)-liphagal

Published: August 21, 2015The 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.Adrian W. Markwell-Heys, Kevin K. W. Kuan, and Jonathan H. Georg

Biomimetic synthetic studies on meroterpenoids from the marine sponge Aka coralliphaga: divergent total syntheses of siphonodictyal B, liphagal and corallidictyals A–D

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.Kevin K.W.Kuan, Adrian W.Markwell-Heys, Michelle C.Cruickshank, Denise P.Tran, Robert M.Adlington, Jack E.Baldwin, Jonathan H.George