The marine bacterium "Pseudoalteromonas januaria" SUT 11 isolated from a seawater sample produced the rare cell-bound cyclic lipodepsipeptides A/A', B/B', and C/C'. The matrix-assisted laser desorption/ionization mass spectra indicated that one bromine atom presented in the peptides B/B' and C/C', whereas the component A/A' contained no bromine atom. The acyldepsipeptides A/A'-C/C' have an identical amino acid sequence, Thr-Val-Asn-Asn-Leu/allo-Ile, but differed in C-terminal amino acid and acyl moieties. Peptides A-C have Leu as a C-terminal amino acid, whereas peptides A'-C' have allo-Ile. Acyl moieties in peptides A/A', B/B', and C/C' have been found to consist of 11-(4'-hydroxyphenyl)-undeca-2,4,6,8,10-pentaenic acid, 9-(3'-bromo-4'-hydroxyphenyl)-nona-2,4,6,8-tetraenic acid, and 11-(3'-bromo-4'-hydroxyphenyl)-undeca-2,4,6,8,10-pentaenic acid, respectively. The structure of a main pair of peptides B/B' with molecular masses 843/845 Da has been determined by means of ultraviolet, infrared, and two-dimensional nuclear magnetic resonance spectroscopy. We have demonstrated that tandem nano-electrospray ionization mass spectrometry is a very efficient way for the fast and sensitive investigation of lipopeptides A/A' and C/C' with molecular masses 791 and 869/871 Da, respectively, which have been isolated in small amounts.