Thushara Diyabalanage

Palmadorins A--C, diterpene glycerides from the antarctic nudibranch Austrodoris kerguelenensis.

The nudibranch Austrodoris kerguelenensis is distributed widely around the Antarctic coast and continental shelves. Earlier collections from McMurdo Sound and the Weddell Sea shelf have afforded a suite of diterpene glyceride esters, a compound class implicated as a chemical defense in nudibranchs. The present chemical investigation of A. kerguelenensis collected near Palmer Station on the Western Antarctic Peninsula has revealed additional examples, palmadorins A-C (1-3), as the first three members of a new series of clerodane diterpenes. In this paper we describe their isolation, structure elucidation, and stereochemical analysis using a combination of one- and two-dimensional NMR spectroscopy and wet chemical methods.

Palmerolide macrolides from the Antarctic tunicate Synoicum adareanum

Palmerolides D-G are new bioactive macrolides isolated from the Antarctic tunicate Synoicum adareanum and are related to the melanoma-selective cytotoxin palmerolide A. Most of these palmerolides are potent V-ATPase inhibitors and have sub-micromolar activity against melanoma. Though palmerolide A remains the most potent of this series of natural products against mammalian V-ATPase, recent data suggests that palmerolide D is the most potent against melanoma. A comparison of the bioactivity data obtained for these natural product palmerolides has provided insight into the substructures necessary to retain V-ATPase inhibition and cytotoxic activity.

Flabelliferins A and B, sesterterpenoids from the South Pacific sponge Carteriospongia flabellifera.

Two new sesterterpenoids named flabelliferins A (1) and B (2) were isolated from the lipophilic extract of the sponge Cateriospongia flabellifera, collected in the South Pacific near Vanuatu. The structure and absolute configuration of these two compounds were assigned by a combination of one- and two-dimensional NMR spectroscopy and by Moshers ester analysis. Flabelliferin A (1) has a rare 25-homocheilanthane carbon skeleton, while flabelliferin B (2) is a 24-nor-25-homoscalarane sesterterpenoid.

Nothospondin, a new AP-1 inhibitory quassinoid from the Cameroonian plant Nothospondias staudtii

A high throughput screen for inhibitors of the oncogenic transcription factor activator protein-1 (AP-1) was applied to the NCI repository of natural product extracts. The liphophilic extract of the plant Nothospondias staudtii (Simaroubaceae) displayed significant AP-1 inhibition. Bioassay-guided fractionation of the extract lead to a new quassinoid named nothospondin (1), and the known compound glaucarubinone (2). The structure of 1 was elucidated by spectroscopic methods. Compounds 1 and 2 showed potent, dose-dependent AP-1 inhibition at noncytotoxic concentrations.