Two new cyclic tetrapeptides from deep-sea bacterium bacillus amyloliquefaciens GAS 00152

Marine microorganisms continue to be a productive focus for much of marine natural products investigation.^{1, 2, 3} These organisms flourishing in diverse marine environments, have produced a wide variety of structurally unique and biologically active secondary metabolites many of which have attracted considerable attention.^{1, 4} In the last decades, the number of reported secondary metabolites from marine bacteria has steadily increased.2 Medium ring-sized peptides containing the amino acids leucine, isoleucine, phenylalanine, valine and proline have been reported from diverse marine sources, including microorganisms.^{5, 6} The genus Bacillus has produced biologically active compounds.^{7, 8} In our search for bioactive natural products from the bacterium B. amyloliquefaciens collected from South China Sea deep-sea sediment, the culture broth contained two new cyclic tetrapeptides, cyclo-(Leu-Pro-Ile-Pro) (1) and cyclo-(Tyr-Pro-Phe-Gly) (2) (Figure 1).