Neal Frederick Osborne

Molecular recognition of tyrosinyl adenylate analogues by prokaryotic tyrosyl tRNA synthetases.

Molecular modelling and synthetic studies have been carried out on tyrosinyl adenylate and analogues to probe the interactions seen in the active site of the X-ray crystal structure of tyrosyl tRNA synthetase from Bacillus stearothermophilus, and to search for new inhibitors of this enzyme. Micromolar and sub-micromolar inhibitors of tyrosyl tRNA synthetases from both B. stearothermophilus and Staphylococcus aureus have been synthesised. The importance of the adenine ring to the binding of tyrosinyl adenylate to the enzyme, and the importance of water-mediated hydrogen bonding interactions, have been highlighted. The inhibition data has been further supported by homology modelling with the S. aureus enzyme, and by ligand docking studies.

6-(SUBSTITUTED METHYLENE)PENEMS, POTENT BROAD SPECTRUM INHIBITORS OF BACTERIAL β-LACTAMASE

Sodium (5RS)-Z-6-(heterocyclylmethylene)penem-3-carboxylates (2) are a series of extremely potent inhibitors of bacterial beta-lactamases. A variety of 5-membered heteroaromatic derivatives have been prepared and structure-activity studies reveal a preferred substituent orientation. One of these derivatives, the 1-methyl-1,2,3-triazolyl compound (5m) is a more potent synergist of amoxycillin than clavulanic acid, sulbactam or tazobactam.

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.

A novel and stereocontrolled synthesis of (5R)-(Z)-6-(1-methyl-1,2,3-triazol-4-ylmethylene)penem-3-carboxylic acid, a potent broad spectrum β-lactamase inhibitor

The key step in the preparation of the title compound (BRL 42715) from 6-aminopenicillanic acid was the condensation of the anion, generated by deprotonation of p-methoxybenzyl (5R,6S)-6-bromopenem-3-carboxylate(10), with 1-methyl-1,2,3-triazole-4-carbaldehyde; in situ acylation, followed by reductive elimination afforded the isomeric (Z)- and (E)-6-triazolylmethylene penem esters, (12) and (13) respectively.

Synthesis of (5R)-(Z)-6-(1-methyl-1,2,3-triazol-4-ylmethylene)penem-3-carboxylic acid, a potent broad spectrum β-lactamase inhibitor, from 6-aminopenicillanic acid

(5R)-(Z)-6-(1-Methyl-1,2,3-triazol-4-ylmethylene)penem-3-carboxylic acid 34(BRL 42715) has been prepared from 6-aminopenicillanic acid 4(6-APA) by a short, stereoselective and efficient route via the novel intermediate, p-methoxybenzyl (5R, 6S)-6-bromopenem-3-carboxylate 17.Elaboration of 6-APA 4 to the azetidinone disulfide 10 by established methodology, followed by reductive formylation provided the crystalline C-4 formylthio-azetidinone derivative 29. Cyclization of the oxalimide 28, obtained by ozonolysis of the formylthio derivative 29, to the crystalline 6α-bromopenem ester 17 was effected by way of the phosphite-mediated carbonyl–carbonyl coupling reaction.Sequential treatment of bromopenem 17 with lithium diphenylamide, 1-methyl-1,2,3-triazole-4-carbaldehyde, and acetic anhydride gave a diastereoisomeric mixture of acylated bromohydrins 32; reductive elimination of this mixture afforded a separable mixture of (Z)- and (E)-triazolylmethylene penem esters, 33 and 35 respectively. Lewis acid-mediated deprotection of ester 33 provided (5R)(Z)-6-(1-methyl-1,2,3-triazol-4-ylmethylene)penem-3-carboxylic acid 34(BRL 42715) as a crystalline sodium salt monohydrate.The 6-heterocyclylmethylene penems, represented by BRL 42715, are potent inhibitors of bacterial β-lactamases and their combination with an appropriate penicillin or cephalosporin results in good synergistic activity against a broad range of β-lactamase-producing bacteria.