Total synthesis and structure revision of petrobactin

The total synthesis and the revised structural assignment of petrobactin, a siderophore isolated from the marine bacterium Marinobacter hydrocarbonoclasticus, is reported. The key step in the synthesis involved condensation of N1-(2,3-dibenzoyloxybenzoyl)-N4-benzylspermidine with 1,3-di-(p-nitrophenyl)-2-tert-butyl citrate. Proton NMR spectra of the synthesized product compared with those reported for the natural product revealed that the compound did not contain 2,3-dihydroxybenzoyl moieties as published; instead, the splitting pattern suggested 3,4-dihydroxybenzoyl fragments. The 3,4-dihydroxybenzoyl analogue was accessed via a similar route; the proton and carbon-13 NMR spectra of this compound were consistent with those reported for natural petrobactin.