Dennis D. Keith

Growth inhibition by methionine analog inhibitors of S-adenosylmethionine biosynthesis in the absence of polyamine depletion

Four methionine analog inhibitors of methionine adenosyltransferase, the enzyme which catalyzes S-adenosylmethionine biosynthesis, were tested in cultured L1210 cells for their effects on cell growth, leucine incorporation, S-adenosylmethionine (AdoMet) formation and polyamine biosynthesis. The IC50 values were as follows: selenomethionine, 0.13 mM; L-2-amino-4-methoxy-cis-but-3-enoic acid (L-cis-AMB), 0.4 mM; cycloleucine, 5 mM and 2-aminobicyclo[2.1.1]hexane-2-carboxylic acid, 5 mM. At IC50 levels, the analogs significantly reduced AdoMet pools by approximately 50% while not similarly affecting leucine incorporation or polyamine biosynthesis. In combination with inhibitors of polyamine biosynthesis, growth inhibition was greatly increased with methylglyoxal bis(guanylhydrazone), an inhibitor of AdoMet decarboxylase, but only slightly increased with alpha-difluoromethylornithine, an inhibitor of ornithine decarboxylase. Overall, the data indicate that the methionine analogs, and particularly L-cis-AMB, seem to inhibit cell growth by interference with AdoMet biosynthesis. Since polyamine biosynthesis is not affected, the antiproliferative effect may be mediated through perturbations of certain transmethylation reactions.

A comparison of the antibacterial and β-lactamase inhibiting properties of penam and (2,3)-β-methylenepenam derivatives : The discovery of a new β-lactamase inhibitor. Conformational requirements for penicillin antibacterial activity

Abstract The antibacterial potencies of 2a and 4 are shown to be diminished considerably from their penam analogues, penicillin G (1a) and mecillinam (3). Despite this, 2a is a substrate for bacterial β-lactamases, and compounds 6a, 8 and 10 were found to be β-lactamase inhibitors. Penicillin-binding protein (PBP) studies indicate that penicillin G and mecillinam have much greater affinity for these enzymes than the (2,3)-β-methylenepenam analogues. Based on a comparison of hydrolytic stabilities, it is proposed that the change in biological properties is due to conformational differences between the two types of penam nuclei. The cyclopropyl methylene of 2a and 4 blocks the side chain from forming an oxazolone with the β-lactam carbonyl. Hence, activation of the β-lactam is prevented and the molecules are rendered less active. We thus conclude that 19 is the biologically active conformation of penicillin antibacterials, and further suggest that the interaction of such antibiotics with their bacterial enzyme targets involves intermediates such as 25–27.

L-2-Amino-4-methoxy-cis-but-3-enoic acid, a potent inhibitor of the enzymatic synthesis of S-adenosylmethionine.

Abstract L -2- Amino -4- methoxy - cis - but -3- enoic acid was synthesized and found to be an extremely potent inhibitor of ATP: L-methionine adenosyltransferase isozymes of rat liver and Novikoff solid hepatoma. The inhibitory potency of L -2- amino -4- methoxy - cis - but -3- enoic acid was found to be significantly higher than that of its structural analogues, L-methoxinine and L -2- amino -4- methoxy - trans - but -3- enoic acid . The Ki values of L -2- amino -4- methoxy - cis - but -3- enoic acid and the Km values of L-methionine are comparable for the rat liver and tumor isozymes, suggesting a close correlation between the enzyme-bound conformations of these two molecules.

In vivo Evaluation of a Dual-Action Antibacterial, Ro 23-9424, Compared to Cefotaxime and Fleroxacin

The dual-action antibacterial R 23-9424 (desacetylcefotaxime linked to the quinolone fleroxacin) is a new antibacterial agent with excellent in vitro activity. It was evaluated for in vivo efficacy in comparison with the cephalosporin cefotaxime and the quinolone component, fleroxacin. Ro 23-9424 demonstrated significant activity against all strains tested in systemic infections, including those strains resistant in vivo to cefotaxime (Staphylococcus aureus 753, Serratia marcescens SM and Pseudomonas aeruginosa 8780) and fleroxacin (Streptococcus pneumoniae 6301 and Streptococcus pyogenes. In prophylactic studies, Ro 23-9424 compared favorably with fleroxacin against Escherichia coli and with cefotaxime against S. pyogenes, but Ro 23-9424 was considerably more active than cefotaxime against E. coli and more active than fleroxacin against S. pyogenes. In a murine pneumonia model, Ro 23-9424 was equivalent in activity to cefotaxime against S. pneumoniae and more active than cefotaxime against Klebsiella pneumoniae. Fleroxacin was inactive against S. pneumoniae and about 20-fold more active than Ro 23-9424 against K. pneumoniae. In a murine meningitis infection caused by S. pneumoniae, Ro 23-9424 was 3 times as active as cefotaxime, while fleroxacin was inactive. When meningitis was induced by K. pneumoniae, Ro 23-9424 was as active as the quinolone, while cefotaxime was inactive. In a neutropenic (immunocompromised) model, Ro 23-9424 was more active than cefotaxime against P. aeruginosa and 5-fold less active than fleroxacin. In the control normal (immunocompetent) mouse infection, Ro 23-9424 was 3-fold more active than cefotaxime, but 10-fold less active than fleroxacin.

Synthesis of Potential Transition State Inhibitors of Succinyl CoA: Tetrahydrodipicolinate N-Succinyltransferase

The preparation of 2-hydroxytetrahydropyran-2,6-dicarboxylic acid (6S-1), 2-hydroxytetrahydrofuran-2,5-dicarboxylic acid (17), and 3,3-difluoro-2-hydroxytetrahydropyran-2,6-dicarboxylic acid (26), three transition state analogs of hydrated tetrahydrodipicolinic acid (THDPA) and a depsipeptide derivative (11) of 6S-1 is described

Synthesis of a highly reactive 1,1-dicyanomethylene-1-dethiacephalosporin

Synthesis of the 1,1-dicyanomethylene-1-dethiacephalosporin 1a is described. Substitution of the dicyanomethylene moiety for sulfur at position 1 of the cephem nucleus resulted in a highly reactive β-lactam antibacterial.

A novel synthesis of oxanosine and 1-thiaguanosine

Abstract A novel total synthesis of oxanosine has been developed. The key heterocycle forming reaction of this synthesis is the carbodiimide mediated dehydration and cyclization of an urea-acid derived from AICA-riboside. The same procedure was also applied to the synthesis of 1-thiaguanosine.

Stipitatic acid: synthesis via cyclopropanated quinones

Abstract A new synthesis of stipitatic acid incorporating a cyclopropanated quinone intermediate is reported.

(2,3)-α-methylenepenicillanic acid sulfone: synthesis and β-lactamase inhibiting properties

Abstract The synthesis and β-lactamase inhibiting properties of 2,3-α-methylenepenicillanic acid sulfone (3) are described. The results presented are consistent with previous work indicating that β-lactamases recognize α-methylenepenams as cephalosporins.

(2,3)-(α-methylenepenams: Synthesis and in vitro activity

Abstract A series of α-methylene penicillins was synthesized and SAR were studied. The α-isomers were found to be chemically reactive and biologically active in contrast to the β-isomers. In addition, the α-isomers have broader spectrum of in vitro activity than the corresponding penicillins. Generally, the α-isomers are more active against gram-negative bacteria than the corresponding penicillins, but slightly weaker in potency towards gram-positive organisms.