Lopez Julius Adam Velasco, Al-Lihaibi Sultan S., Alarif Walied M., Abdel-Lateff Ahmed, Washio Kenji, Morikawa Masaaki, Okino Tatsufumi
Symposium on the Chemistry of Natural Products, symposium papers 天然有機化合物討論会実行委員会 57 PosterP23 2015
Cyanobacteria are prolific sources of novel bioactive compounds. The chemical profiles we obtained using LC-MS and checked with the MarinLit database showed that there are potential new compounds from Moorea producens samples obtained from the Red Sea. In this presentation the isolation and structure elucidation of a new cyclic dodecapeptide, wewakazole B (1), is reported.
The brownish-red filamentous sample was obtained by SCUBA near Jeddah, Saudi Arabia. A small portion of the sample was preserved in RNAlater and identified as M. producens by standard 16S rRNA gene sequencing using cyanobacteria-specific primers 106F and 1509R, and internal primers 359F and 781R (Martinez-Murcia et al., 1995; Nubel et al., 1997). The bulk of the sample was extracted with methanol followed by solvent partition using EtOAc and water, then, BuOH. These extracts were tested for antifouling activity against the barnacle larvae Amphibalanus amphitrite, cytotoxicity against MCF-7 breast cancer cells, and trypsin inhibition. LC-MS was carried out in parallel for dereplication in conjunction with the MarinLit database. The extracts were found to be inactive but a unique [M+H]+ m/z of 1127 was detected in the EtOAc extract and was pursued. A series of open column chromatography and HPLCs afforded 0.4 mg of 1.
The molecular formula, C58H70N12O12, determined by HRESIMS ([M+H]+ m/z1127.5310, ∆ = 0.39 ppm), suggested thirty unsaturations. Dereplication using mass and 1H NMR data showed wewakazole (Nogle et al., 2003) as the nearest candidate. HSQC, COSY, and TOCSY revealed nine common and three modified amino acid residues which were connected by HMBC and ROESY correlations acquiring five fragments. Connections to the oxazole and methyloxazole fragments proved to be a challenge due to the lack of correlations towards neighboring amino acids. All possible combinations were considered that lead to the most logical planar structure and cyclic sequence. Chiral LC-MS and HPLC analysis showed that all amino acid residues possess the L- configuration. The wewakazoles are the only cyclic peptides from marine cyanobacteria having both Oxz and MeOxz. Their function and bioactivity require further investigation.