Serratiomycins D1–D3, Antibacterial Cyclic Peptides from a <i>Serratia</i> sp. and Structure Revision of Serratiomycin
Young Eun Du, Jinsheng Cui, Eunji Cho, Sunghoon Hwang, Yong-Joon Jang, Ki‐Bong Oh, Sang‐Jip Nam, Dong‐Chan Oh
Abstract
Serratiomycin ( 1 ) is an antibacterial cyclic depsipeptide, first discovered from a Eubacterium culture in 1998. This compound was initially reported to contain l -Leu, l -Ser, l - allo -Thr, d -Phe, d -Ile, and hydroxydecanoic acid. In the present study, 1 and three new derivatives, serratiomycin D1–D3 ( 2 – 4 ), were isolated from a Serratia sp. strain isolated from the exoskeleton of a long-horned beetle. The planar structures of 1 – 4 were elucidated by using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy. Comparison of the NMR chemical shifts and the physicochemical data of 1 to those of previously reported serratiomycin indeed identified 1 as serratiomycin. The absolute configurations of the amino units in compounds 1 – 4 were determined by the advanced Marfey’s method, 2,3,4,6-tetra- O -acetyl-β- d -glucopyranosyl isothiocyanate derivatization, and liquid chromatography–mass spectrometric (LC–MS) analysis. Additionally, methanolysis and the modified Mosher’s method were used to determine the absolute configuration of (3 R )-hydroxydecanoic acid in 1 . Consequently, the revised structure of 1 was found to possess d -Leu, l -Ser, l -Thr, d -Phe, l - allo -Ile, and d -hydroxydecanoic acid. In comparison with the previously published structure of serratiomycin, l -Leu, l - allo -Thr, and d -Ile in serratiomycin were revised to d -Leu, l -Thr, and l - allo -Ile. The new members of the serratiomycin family, compounds 2 and 3, showed considerably higher antibacterial activities against Staphylococcus aureus and Salmonella enterica than compound 1 .