Abstract:
The genus Dysidea is a remarkable source of novel secondary metabolites. It is predominantly a producer of sesquiterpenes but, non-terpenoid compounds including halogenated amino acid derivatives and brominated phenyl ethers have been consistently isolated from collections of Dysidea herbacea.
In this study a collection of Dysidea from the Wellington coast, New Zealand, was investigated for secondary metabolite content. Crude reverse phase column chromatography followed by exhaustive HPLC chromatography revealed a number of sesquiterpenes (457-471) representing four separate carbon skeleton classes.
The tricyclic skeletons of compounds 457-460 are representatives of the carbon skeleton identified from nakafuran-8. Compound 457 has been identified but without NMR assignment. Compounds 458-460 represent new variations in this class.
The second class of compounds exhibit the carbon skeleton of several of the identified microcionins. Compounds 466 and 467 have recently been published, but 461 and 462 and their methylated derivatives (463-465) represent new additions to this class.
The third carbon skeleton class consists of three members including the two known dysinin butenolides 459 and 470, and their novel antipodean relative compound 468.
Compound 471 was the final compound isolated from this study. The structure elucidated represents a previously unreported tetracyclic sesquiterpene carbon skeleton. It was given the archaic name of Ponekenolide (471) in reference to the NZ Maori word for Wellington (Poneke), the area from which the sponge collection was made.
In addition to the structural novelty of several of the isolated compounds, epimerisation at a common biogenetic stereocentre was observed for three pairs of compounds (457/458, 461/462, 463/464). More remarkable was the revelation using X-ray crystal analysis, that both enantiomers of compound 457 were present in a single crystal.
