New cyclic tetrapeptide from the coral-derived endophytic bacteria Brevibacterium sp. L-4 collected from the South China Sea.

One new cyclic tetrapeptide cyclic-(Tyr-Ala-Leu-Ser) (1) along with four natural compounds firstly obtained 3H-imidazole-4-carboxylic acid (2), 2-methyl-3H-imidazole-4-carboxylic acid (3), 3-ethylidene-6-isopropyl-piperazine-2,5-dione (4), and 3-isobutylidene-6-methyl piperazine-2,5-dione (5) have been isolated from the coral derived endophytic bacteria Brevibacterium sp. L-4 collected from the South China Sea. Their structures were elucidated through spectroscopic techniques including NMR (1D and 2D), MS, and EA, and their relative configurations were also assigned by NMR analysis.