Oxygenated N-Acyl Alanine Methyl Esters (NAMEs) from the Marine Bacterium Roseovarius tolerans EL-164

Abstract

The marine bacterium Roseovarius tolerans EL-164 (Rhodobacteraceae) can produce unique N-acylalanine methyl esters (NAMEs) besides strucutrally related N-acylhomoserine lactones (AHLs), bacterial signaling compounds widespread in the Rhodobacteraceae. The structures of two unprecedented NAMEs carrying a rare terminally oxidized acyl chain are reported here. The compounds (Z)-N-16-hydroxyhexadec-9-enoyl-l-alanine methyl ester (Z9-16-OH-C16:1-NAME, 3) and (Z)-N-15-carboxypentadec-9-enoyl-l-alanine methyl ester (16COOH-C16:1-NAME, 4) were isolated, and the structures were determined by NMR and MS experiments. Both compounds were synthesized to prove assignments and to test their biological activity. Finally, non-natural, structurally related Z9-3-OH-C16:1-NAME (18) was synthesized to investigate the mass spectroscopy of structurally related NAMEs. Compound 3 showed moderate antibacterial activity against microorganisms such as Bacillus, Streptococcus, Micrococcus, or Mucor strains. In contrast to AHLs, quorum-sensing or quorum-quenching activity was not observed.

N-Acylated amino acid methyl esters from marine Roseobacter group bacteria

“…The NAMEs, NABMEs and NAVMEs reported here were detected by MS 2 analyses based on their characteristic fragmentation (see below). The only oxygenated derivative present was 16OH-C16:1-NAME, which has been described before from Roseovarius tolerans EL-164 [24].…”

“…The MS 2 spectrum of the [M + H] + -ion obtained in ESI positive mode shows loss of water, an intense ion due to loss of methanol, and loss of the carbomethoxy group [24]. Often the amino acid ion can also be observed.…”

“…Instead, they show moderate antialgal activity [21]. In contrast to AHLs, the acyl chain can also be terminally oxidized [24]. During our analyses of different Roseobacter isolates, we encountered several compounds, which mass spectra show similarities to known NAMEs.…”

An Unprecedented Medium-Chain Diunsaturated N-acylhomoserine Lactone from Marine Roseobacter Group Bacteria

“…280.19072) required for an diunsaturated AHL. The homoserine lactone unit is indicated by the ion m/z 102.05496 (C 4 H 8 NO 2 ) and the acyl chain by the ion m/z 179.14314 (C 12 H 19 O) in the ESI spectrum [18]. The location of the double bonds could not be determined with dimethyl disulfide derivatization [12,20] because of the low concentration of the compound.…”

“…This approach combines high-sensitivity with unbiased analysis and allows structural proposals to be made basing on the information rich EI-mass spectra obtained. We could successfully use this approach to identify several previously unknown AHLs [12,15,16] as well as related N -acylalanine methyl esters (NAMEs) [17,18]. We have previously analyzed AHLs from roseobacters isolated from macroalgae surfaces and found a high proportion of strains producing AHLs in various mixtures [12].…”