Abstract
Extracts of the mantle and viscera of the Indo-Pacific nudibranchs Goniobranchus aureopurpureus and Goniobranchus sp. 1 afforded 11 new diterpenoids (1–11), all of which possess a tetracyclic spongian-16-one scaffold with extensive oxidation at C-6, C-7, C-11, C-12, C-13, and/or C-20. The structures and relative configuration were investigated by NMR experiments, while X-ray crystallography provided the absolute configuration of 1, including a 2′S configuration for the 2-methylbutanoate substituent located at C-7. Dissection of animal tissue revealed that the mantle and viscera tissues differed in their metabolite composition with diterpenes 1–11 present in the mantle tissue of the two nudibranch species.
Highlights
Spongian diterpenes are bioactive natural products isolated from sponges of the orders Dictyoceratida and Dendroceratida, and nudibranchs predators [1,2].The first example of the spongian diterpene scaffold was isoagatholactone, isolated from the Mediterranean sponge Spongia officinalis by Cimino et al, and with the structure and absolute configuration established through chemical correlation with grindelic acid [3].The metabolites spongian-16-one and spongian-15,16-dione were isolated from the NewZealand sponge Dictyodendrilla cavernosa [4]
Spongian-16-one has been isolated from several nudibranch species, including Chromodoris obsoleta and exhibits moderate anti-neoplastic activity against L1210 (IC50 = 5.0 μg mL−1 ) and KB
(IC50 = 9.2 μg mL−1 ) cell lines [6]. In this group of tetracyclic diterpenes, further oxidation is commonly seen at C-7, C-11, C-12, C-13, C-15, C-17, and/or C-20 [7]
Summary
Spongian diterpenes are bioactive natural products isolated from sponges of the orders Dictyoceratida and Dendroceratida, and nudibranchs (shell-less mollusc) predators [1,2]. Spongian-16-one has been isolated from several nudibranch species, including Chromodoris obsoleta and exhibits moderate anti-neoplastic activity against L1210 (IC50 = 5.0 μg mL−1 ) and KB (IC50 = 9.2 μg mL−1 ) cell lines [6]. In this group of tetracyclic diterpenes, further oxidation is commonly seen at C-7, C-11, C-12, C-13, C-15, C-17, and/or C-20 [7]. The structures and relative configuration of eleven isolated diterpene metabolites were determined by analysis of their two-dimensional NMR spectra as well as where applicable by X-ray crystallography to determine the absolute configuration.
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