Isolation and Characterisation of Bioactive Secondary Metabolites from Arctic, Marine Organisms

Abstract

The list of achievements in developing pharmaceuticals and other useful products originating from Nature is long, and it continues to extend. Marine bioprospecting alone has generated three novel drugs in the last four years. The continued success motivates further bioprospecting efforts in the search for utilisable products from natural sources.

In this thesis, extracts of Arctic marine organisms were screened for bioactivity. Bioactive extracts were dereplicated using high-resolution mass spectrometry (HR-MS) in an attempt to identify the component(s) responsible for the observed bioactivity and later isolate them using mass guided fractionation. This approach led to the isolation of ianthelline, a previously reported bromotyrosine-derived compound from the sponge Stryphnus fortis as well as two novel, highly modified dipeptides, breitfussin A and B, from the hydrozoa Thuiaria breitfussi.

Even though the structure of ianthelline was reported in 1986 by Litaudon et al. very limited bioactivity data was available. The potential of ianthelline as an anticancer agent was explored in paper I. Ianthelline inhibited cellular growth in a dose- and time dependent manner by several mechanisms, including inhibition of mitotic spindle formation and inhibition of protein kinase activity. In paper II, ianthelline was investigated for antibiofouling activity. The compound was found to inhibit all the major stages of the biofouling process, with the main effect being inhibition of marine bacterial growth and the settlement of barnacles.

By dereplication, breitfussin A and B were suspected to be novel compounds, with proton poor molecular compositions of C16H11N3O2BrI and C16H11N3O2Br2, respectively. The high ratio of heavy atoms to protons, in addition to low isolation yields, complicated the structure elucidation of the two compounds. In the end, their structures could be elucidated using a combination of HR-MS analysis, nuclear magnetic resonance (NMR) spectroscopy, computer-assisted structure elucidation (CASE)- and density functional theory (DFT) calculations as well as atomic force microscopy (AFM) imaging. This represents the first example of AFM as a tool used for structure elucidation of a novel, natural product.