Bioactive compounds from New Zealand marine organisms

Abstract

Primary screening of recent collections from the sea around New Zealand revealed a wide range of bioactivities, including antitumour, antiviral and anti-HIV activities. Seven marine organisms, including sponges and an ascidian, were examined to identify the active compounds responsible for these three type of biological activities. A chemical screening protocol was established for the dereplication and prioritization of antiviral natural product extracts, which was also applied to extracts with other bioactivities. A recent modification included HPLC analysis of the eluates from solid phase extraction cartridges, coupling the UV profiles of the corresponding peaks in the HPLC traces with MarinLit database. Extracts from two marine sponges which contained known cytotoxic compounds, pateamine and calyculins respectively, were used to test the efficiency of the modified protocol. These two types of active compounds were quickly identified by searching the UV data field in MarinLit. HIV -inhibitory activity was recognised in both aqueous and organic extracts from a sponge Chondropsis kirkii. The aqueous extract was processed on a Sephadex-25 column. The positive results of a toluidine blue test on the resultant fractions suggested that sulphated polysaccharides may be responsible for the potent anti-HIV activity. The HIV -inhibitory components in the organic extract turned out to be a mixture of sterols. However, an increase of the cytotoxicity with increasing sample purity was also observed. Examination of a sponge Callyspongia irregularis resulted in the isolation of a known compound, mycalamide A, which is a potent antiviral agent. Purification of the trace amount of compound obtained was mainly achieved by high speed countercurrent chromatography (HSCCC). Examination of another Callyspongia species has led to the discovery of a potently cytotoxic fraction (IC₅₀ 11 ng/mL). A New Zealand deep water sponge, Lamellomorpha strongylata, has turned out to be a rich source of bioactive compounds. Bioassay-guided analysis led to the separation of five new cytotoxic theonellapeptolides IIIa, IIIb, IIIc, IIId and IIIe (molecular-weight 1376-1453). These tridecapeptides were characterised by amino acid analysis using GC-MS, sequencing the ring-opened peptides with FABMS-MS, and ID (¹H, ¹³C, DEPT and decoupling experiment) and 2D (COSY, TOCSY, HMQC-TOCSY, HMBC, HSMQC and ROESY) NMR, IR analysis and chemical reaction. Of these, the MS-MS technique played a very important role in sequencing. These compounds exhibited weak cytotoxicity. However, the other member of the theonellapeptolide family showed ion-transport properties. The absolute stereochemistry of IIIe was determined by X-ray crystal structure analysis in conjunction with a chiral HPLC method. The solution conformations of IIIb and IIIe were established mainly by correlations in the ROESY spectra. Six optically pure N-methyl amino acids were synthesised for a study of the stereochemistry of the component amino acids. The absolute stereochemistry of IIIa, IIIb, IIIe and IIId were determined by chiral LC-MS analysis. In addition, three minor components were isolated from the same sponge. ¹H NMR spectra showed that they all contained peptide components.