This weeks’ offering comes once again from Australia, the Williams group at the University of Queensland collaborating with the Parson’s group at the Queensland Institute of Medical Research and Redell and Gordon from EcoBiotics. They have all been busy examining extracts from Croton insularis found in the Australian rain forest. This group of plants has delivered some interesting biologically active molecules for example phorbols, clerodanes and halimanes being examples.

The group managed to isolate and identify a novel class of diterpene with a bicyclo[10.2.1] ring system containing a rare bridghead olefin, an anti-Bredt system, which is not commonly found in natural products but who’s existence and stability is also influenced by ring size.

The mushed up plant stems (3.6 kg) were exhaustively extracted with ethanol over a period of some days and produced 450 mL of a brown residue, after removal of the ethanol. Further extraction and extensive chromatography led to the isolation of 0.94 mg of the new compound as a colourless oil.

Going through the usual spectroscopic measurements and a few “simple” calculations suggested the following structure for the new compound:

Its name is 1R,2Z,4S,6R,9E,12S)-1,12-dihydroxy-2,5,5,9-tetramethyltricyclo[11.2.1.0^4,6]hexadeca-2,9,13-trien-15-one. Of course the main structural feature is the anti-Bredt olefin and the one carbon bridge formed between C2 and C5.

There are three other known examples of this system but lacking the bridge and the authors suggest a biosynthetic pathway for the formation of the bridged system from the other three. The compound was tested against a variety of human cancer cell lines and was inactive.