Discovery of anti-mycobacterial natural products from South African marine algae
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Tuberculosis is a communicable disease which affects millions of people around the world. Although the case reports are declining, the eradication rate of this disease is far too slow. Natural products have played a key role in the treatment of the disease. However, tuberculosis is developing resistance to current first-line therapy. In this study, a prefractionated marine algal library was developed in order to identify and prioritise samples for isolation of their active metabolites which exhibit anti-tuberculosis activity. Based on the results of the library screening and chemical profiling, two seaweeds were selected for further investigation, Laurencia glomerata and Plocamium cornutum. The extraction and fractionation of Laurencia glomerata and Plocamium cornutum resulted in the isolation of three chamigrane seqsuiterpenes (prepacifenol epoxide, johnstonol and one newly proposed structure) and two monoterpenes (cartilagineal and 1,5,6-trichloro-2-(dichloromethyl)-6-methylocta-1,3,7-triene) respectively. The structures of these compounds were elucidated by 1 and 2D NMR data and were confirmed by literature comparisons. Although some of the initial library factions screened showed rather good activity against Mycobacterium tuberculosis, the selected seaweed fractions showed greater activity against M. aurum. The isolated monoterpenes showed moderate cytotoxicity against the cancer cell line MCF-12a and the sesquiterpenes however were more selective for MCF-7. The monoterpenes showed both activity and potential selectivity towards Mycobacterium tuberculosis.