The Burkholderia genus offers a promising potential in medicine because of the diversity of biologically active natural products encoded in its genome. Some pathogenic Burkholderia spp. biosynthesize a specific class of antimicrobial 2-alkyl-4(1H)-quinolones, i.e., 4hydroxy-3-methyl-2-alkenylquinolones (HMAQs) and their N-oxide derivatives (HMAQNOs).Herein, we report the synthesis of a series of six HMAQs and HMAQNOs featuring a trans- 2 double bond at the C2-alkyl chain. The quinolone scaffold was obtained via the Conrad-Limpach approach while the (E)-2-alkenyl chain was inserted through Suzuki-Miyaura cross-coupling under microwave radiation without noticeable isomerization according to the optimized conditions. Subsequent oxidation of enolate-protected HMAQs cleanly led to the formation of HMAQNOs following cleavage of the ethyl carbonate group. Synthetic HMAQs and HMAQNOs were in vitro evaluated for their antimicrobial activity against different Gram-negative and Gram-positive bacteria as well as against fungi and yeasts. The biological results support and extend the potential of HMAQs and HMAQNOs as antimicrobials, especially against Gram-positive bacteria. We also confirm the involvement of HMAQs in the autoregulation of the Hmq system in Burkholderia ambifaria. The Burkholderia genus includes a vast group of Gram-negative bacteria found in diverse ecological niches. 1,2 Some Burkholderia spp. are of serious pathogenic concerns, such as the Centers for Disease Control and Prevention (CDC) Tier 1 select agents 3 Burkholderia pseudomallei and B. malleithe infectious agents of melioidosis 4,5 and glanders, 6 respectively,and the devastating plant crop pathogens B. glumae and B. gladioli, which cause major yield losses in rice productions. 7,8 Others, like those forming the B. cepacia complex, include species that can both live in beneficial associations with their eukaryotic hots (mammals, plants, and fungi) 2 and cause several hard-to-treat opportunistic infections, such as the cepacian syndrome in individuals suffering from cystic fibrosis. 9Burkholderia spp. offer a tantalizing potential in medicine because of their capacity to produce highly potent and structurally diverse metabolites. 10,11 A plethora of natural products exhibiting various biological functions have been identified or isolated so far from Burkholderia spp. 10 To name few examples, only for B. pseudomallei, cytotoxic siderophores (e.g., malleilactone), 12 proteasome inhibitors (e.g., deoxyglidobactin C), 13 tensioactive lipopeptides (e.g., malleipeptin A), 13 and rhamnolipids, 14 as well as quorum sensing modulators such as N-acyl homoserine lactones (AHLs) 15 and 2-alkyl-4(1H)-quinolones (AQs) 16,17 have been reported.Burkholderia spp. biosynthesize a specific class of AQs, namely 4-hydroxy-3-methyl-2alkenylquinolones (HMAQ, 1-3), which feature a methyl group at C3 and a trans- 2 insaturation at the C2-alkyl chain (Figure 1). [17][18][19][20][21][22][23][24][25][26][27] HMAQs 1 and 3, respectively the heptenyl and nonenyl congeners, exhi...

<p>Rhamnolipids are a specific class of microbial surfactants, which hold great biotechnological and therapeutic potential. However, their exploitation at the industrial level is hampered because they are mainly produced by the opportunistic pathogen <i>Pseudomonas aeruginosa</i>. The non-human pathogenic bacterium <i>Pantoea ananatis</i> is an alternative producer of rhamnolipid-like metabolites containing glucose instead of rhamnose residues. Herein, we present the isolation, structural characterization, and total synthesis of ananatoside A, a 15-membered macrodilactone-containing glucolipid, and ananatoside B, its open-chain congener, from organic extracts of <i>P. ananatis</i>. Ananatoside A was synthesized through three alternative pathways involving either an intramolecular glycosylation, a chemical macrolactonization or a direct enzymatic transformation from ananatoside B. A series of diasteroisomerically pure (1®2), (1®3), and (1®4)-macrolactonized rhamnolipids were also synthesized through intramolecular glycosylation and their anomeric configurations as well as ring conformations were solved using molecular modeling in tandem with NMR studies. We show that ananatoside B is a more potent surfactant than its macrolide counterpart. We present evidence that macrolactonization of rhamnolipids enhances their cytotoxic and hemolytic potential, pointing towards a mechanism involving the formation of pores into the lipidic cell membrane. Lastly, we demonstrate that ananatoside A and ananatoside B as well as synthetic macrolactonized rhamnolipids can be perceived by the plant immune system, and that this sensing is more pronounced for a macrolide featuring a rhamnose moiety in its native ¹<i>C</i>₄ conformation. Altogether our results prove that macrolactonization of glycolipids can dramatically interfere with their surfactant properties and biological activity.</p>