Bioassay and NMR-GuidedIsolation of Natural Productsfrom Pacific Marine Invertebrates

摘要

In the present study, bioassay and NMR approaches were used in combination to guideisolation of two new and three known compounds. An extract library of New Zealandand Tongan marine invertebrates was screened for activity inhibiting the growth ofSaccharomyces cerevisiae. From this, ‘hits’ were identified and validated and threeNew Zealand sponges and a Tongan ascidian were chosen for bulk extraction. Theseinvertebrates were extracted in methanol and purified using normal and reversed-phasechromatography to isolate the compounds of interest. The isolation of compounds wasguided by either inhibitory activity towards S. cerevisiae, 1H NMR spectroscopy or acombination of the two.The known trihydroxylated steroid (14) was isolated from the calcareous sponge Leucosoleniasp. A fatty acid and mixture of phthalate esters were isolated from anunidentified Tongan ascidian. The fatty acid was proposed to be cis-vaccenic acid (13) onthe basis of 1H and 13C NMR data. The phthalate ester mixture was not purified further.Work on these two compounds was discontinued due to a lack of activity observed in theS. cerevisiae assay and the well-known nature of fatty acids and phthalate esters.Work was also done on an assay targeting the large mechanosensitive channel (MscL) ofbacteria. Some parameters were optimised for this assay, however some work remainsto be done. The screening of the extract library of New Zealand and Tongan marineinvertebrates using this assay was unsuccessful. More studies to better understand thebehaviour of this assay are required, some of which are proposed herein.The extraction of the New Zealand marine sponge Haliclona sp. yielded one known andtwo new 3-alkyl pyridinium alkaloid (3-APA) monomers. The structures of these 3-APAmonomers—dehydrohaliclocyclin C (58), dehydrohaliclocyclin F (59) and the knownhaliclocyclin C (20)—were elucidated using a combination of NMR spectroscopy, massspectrometry (MS) and chemical degradation. This is the first report of a 3-APA cyclicmonomer with unsaturation in the alkyl chain being isolated. 3-APAs were identified asthe source of inhibitory activity in the S. cerevisiae assay, however, no inhibitory activitywas found for 58, 59 and 20 against the clinically relevant fungus C. albicans.