Structure revision of N-mercapto-4-formylcarbostyril produced by Pseudomonas fluorescens G308 to 2-(2-hydroxyphenyl)thiazole-4-carbaldehyde [aeruginaldehyde].

An antibiotic substance isolated from Pseudomonas fluorescens strain G308 was earlier assigned the structure of N-mercapto-4-formylcarbostyril, but computational predictions of the 1H and 13C NMR magnetic shielding tensors show this structure to be incompatible with the published spectroscopic data. The same is true for six quinoline derivatives related to N-mercapto-4-formylcarbostyril by permutation of the O and S atoms. In contrast, 2-(2-hydroxyphenyl)thiazole-4-carbaldehyde [aeruginaldehyde], isolated from Pseudomonas protegens Pf-5, together with the reduced derivative aeruginol, displays spectroscopic data identical with those of the alleged carbostyril derivative. In addition, the published 1H and 13C NMR data are in agreement with those calculated for aeruginaldehyde. We propose that aeruginaldehyde and aeruginol originate from the non-ribosomal peptide synthetase enzymes involved in the siderophores enantio-pyochelin (or pyochelin) biosynthetic pathways.