Heteroaromatic monothiocarboxylic acids from Pseudomonas spp.

Pyridine derivatives substituted with monothiocarboxylic acid groups are the unique metabolites of certain Pseudomonas species. Pyridine-2,6-di-(monothiocarboxylic acid) 1a was found during a screening program for antibiotically active bacterial metabolites due to its ability to complex Fe3+. The structure of this complex, its redox behavior and the biogenesis of the ligand molecule were studied in detail. This lead to the discovery of a new class of natural products, viz. acylsulfenic acid derivatives. Interest in 1a was revived shortly when complexes with other metals were studied as models for sulfur-containing enzymes. It could also be shown that a quinoline monothiocarboxylic acid derivative acted as an alternative siderophore for Pseudomonas fluorescens. But a real renaissance was observed only when the role of 1a in the degradation of CCl4 by Pseudomonas stutzeri became evident.