Pseudomonas fluorescens CHA0 Produces Enantio-pyochelin, the Optical Antipode of the Pseudomonas aeruginosa Siderophore Pyochelin

The siderophore pyochelin is made by a thiotemplate mechanism from salicylate and two molecules of cysteine. In Pseudomonas aeruginosa, the first cysteine residue is converted to its D-isoform during thiazoline ring formation whereas the second cysteine remains in its L-configuration, thus determining the stereochemistry of the two interconvertible pyochelin diastereoisomers as 4 ′R, 2 ″R, 4 ″R (pyochelin I) and 4 ′R, 2 ″S, 4 ″R (pyochelin II). Pseudomonas fluorescens CHA0 was found to make a different stereoisomeric mixture, which promoted growth under iron limitation in strain CHA0 and induced the expression of its biosynthetic genes, but was not recognized as a siderophore and signaling molecule by P. aeruginosa. Reciprocally, pyochelin promoted growth and induced pyochelin gene expression in P. aeruginosa, but was not functional in P. fluorescens. The structure of the CHA0 siderophore was determined by mass spectrometry, thin-layer chromatography, NMR, polarimetry, and chiral HPLC as enantio-pyochelin, the optical antipode of the P. aeruginosa siderophore pyochelin. Enantio-pyochelin was chemically synthesized and confirmed to be active in CHA0. Its potential biosynthetic pathway in CHA0 is discussed.

Studies of Australian soft corals. XXX. A novel trisnorsesquiterpene from a Cespitularia species and the isolation of guaiazulene from a small blue Alcyonium species

A novel trisnorsesquiterpene (1,4-dimethyl-2,3,3a,4,5,6-hexahydroazulene) and an optical antipode of the known sesquiterpene cubebol have been isolated from the soft coral Cespitularia species. The pigment in a small blue Alcyonium species has been identified as guaiazulene.

A total synthesis of the enantiomer of anhydromyriocin (anhydrothermozymocidin)

The optical antipode of anhydromyriocin, the γ-lactone derived from the antibiotic myriocin (thermozymocidin), was synthesized from L-arabinose, establishing the absolute configuration of myriocin as 47. In contrast to its natural enantiomer, it showed but little antifungal activity.