John W. Tyler

The identification of three new biosynthetic intermediates and one further biosynthetic enzyme in the clavulanic acid pathway

Labelling experiments are described that identify three new compounds, N2-(2-carboxyethyl)arginine, 5-guanidino-(2-oxoazetidin-1-yl)pentanoic acid, and 3-hydroxy-5-guanidino-2-(2-oxoazetidin-1-yl)pentanoic acid as biosynthetic precursors of proclavaminic acid and hence clavulanic acid in Streptomyces clavuligerus TCC 27064 and a new amidino hydrolase, which hydrolyses 3-hydroxy-5-guanidino-2-(2-oxoazetidin-1-yl)pentanoic acid to proclavaminic acid has been characterised.

The isolation and characterisation of (3R,5R)- and (3S,5R)-carbapenam-3-carboxylic acid from Serratia and Erwinia species and their putative biosynthetic role

Two new β-lactams (4b) and (5b), and (3S,5R)-carbapenam-3-carboxylic acid, have been isolated from strains of Serratia and Erwinia spp.; their possible role, and that of (5R)-carbapen-2-em-3-carboxylic acid as intermediates in the biosynthesis of the more complex members of the carbapenem family of β-lactam antibiotics is discussed.

Evidence that the immediate biosynthetic precursor of clavulanic acid is its N-aldehyde analogue

(3R, 5R) Clavulanate-9-aldehyde 1 has been detected in Streptomyces clavuligerus and an NADPH dependent dehydrogenase capable of reducing 1 to clavulanic acid 2 has been isolated from this organism.

Ketone–hemiacetal tautomerism in erythromycin A in non-aqueous solutions. An NMR spectroscopic study

NMR spectroscopic studies, including 13C SIMPLE NMR, in a number of solvents, show that erythromycin A exists as a mixture of the 9-ketone (the predominant species), one 6,9-cyclic hemiacetal 3(9-deoxo-6-deoxy-9-hydroxy-6,9-epoxyerythromycin A), and one 9,12-cyclic hemiacetal 2(9-deoxo-12-deoxy-9-hydroxy-9,12-epoxyerythromycin A). Similar studies on the 4″,11-diacetate of erythromycin A, previously thought to be the 6,9-cyclic hemiacetal, show that this exists exclusively as the 9,12-cyclic hemiacetal 4(9-deoxo-12-deoxy-9-hydroxy-9,12-epoxyerythromycin A 4″,11-diacetate) in CDCl3. The (9S) stereochemistry is proposed for 2, 3 and 4. The factors governing tautomerism in erythromycin A and its derivative are discussed.

The chemistry of pseudomonic acid. Part 6. Structure and preparation of pseudomonic acid D

Pseudomonic acid D (1c), a minor antibiotic produced by Pseudomonas fluorescens, has been isolated and identified. The preparation of pseudomonic acid D from monic acid A (1e) is described.

Studies on the mechanism of action of (5R)-(Z)-6-(1-methyl-1,2,3-triazol-4-ylmethylene)penem-3-carboxylic acid (BRL 427 15), a potent inhibitor of bacterial β-lactamase

A novel base catalysed rearrangement of (5R)-(Z)-6-(1-methyl-1,2,3-triazol-4-ylmethylene)penem-3-carboxylic acid (BRL 427 15) is reported together with its implications concerning the mechanism of inactivation of β-lactamases by this compound.

Solubility-Driven Optimization of Phosphodiesterase-4 Inhibitors Leading to a Clinical Candidate

The solubility-driven optimization of a series of 1,7-napthyridine phosphodiesterase-4 inhibitors is described. Directed structural changes resulted in increased aqueous solubility, enabling superior pharmacokinetic properties with retention of PDE4 inhibition. A range of potent and orally bioavailable compounds with good in vivo efficacy in animal models of inflammation and reduced emetic potential compared to previously described drugs were synthesized. Compound 2d was taken forward as a clinical candidate for the treatment of COPD.

N-acyl derivatives of clavaminic acid produced by a mutant of Streptomyces clavuligerus

A mutant of Streptomyces clavuligerus, blocked in clavulanic acid production, was found to accumulate three N-acyl derivatives of the β-lactam clavaminic acid in the culture broth.

Clavulanic acid biosynthesis; the final steps

The chemically unstable anabolite (3R,5R)-clavulanate-9-aldehyde 1 and an NADPH dependent dehydrogenase have been detected in the broth of Streptomyces clavuligerus. The purified enzyme was shown to make clavulanic acid by reduction of the aldehydic moiety of synthetic 1 to the allylic alcohol of clavulanic acid 2. A DNA sequence corresponding to the enzyme’s N-terminal amino acid sequence was located within the clavulanic acid biosynthetic gene cluster. We have named this novel enzyme clavulanic acid dehydrogenase (CAD). In an attempt to determine the origin of 1, fermentations of S. clavuligerus were fed ornithine labelled with stable isotopes in the carboxy group. The results of these experiments are discussed.

Two novel arginine derivatives from a mutant of Streptomyces clavuligerus

Two novel arginine derivatives, N2-(2-carboxyethyl)arginine and N2-(2-carboxyethyl)-3-hydroxyarginine, are produced by a mutant of Streptomyces clavuligerus dclH 65, which is blocked in clavulanic acid biosynthesis, and the structures of the compounds indicate that they may be involved in clavulanic acid biosynthesis.