The thymidine analog 3'-azido-3'-deoxythymidine (BW A509U; azidothymidine [AZT]) had potent bactericidal activity against many members of the family Enterobacteriaceae, including strains of Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, Shigella flexneri, and Enterobacter aerogenes. AZT also had bactericidal activity against Vibrio cholerae and the fish pathogen Vibrio anguillarum. AZT had no activity against Pseudomonas aeruginosa, gram-positive bacteria, anaerobic bacteria, Mycobacterium tuberculosis, nontuberculosis mycobacteria, or,most fungal pathogens. Several lines of evidence indicated that AZT must be activated to the nucleotide level to inhibit cellular metabolism: (i) AZT was a substrate for E. coli thymidine kinase; (ii) spontaneously arising AZT-resistant mutants of E. coli ML-30 and S. typhimurium were deficient in thymidine kinase; and (iii) intact E. coli ML-30 cells converted [3H]AZT to its mono-, di-, and triphosphate metabolites. Of the phosphorylated metabolites, AZT-5'-triphosphate was the most potent inhibitor of replicative DNA synthesis in toluene-permeabilized E. coli pol A mutant cells. AZT-treated E. coli cultures grown in minimal medium contained highly elongated cells consistent with the inhibition of DNA synthesis. AZT-triphosphate was a specific DNA chain terminator in the in vitro DNA polymerization reaction catalyzed by the Klenow fragment of E. coli DNA polymerase I. Thus, DNA chain termination may explain the lethal properties of this compound against susceptible microorganisms.Nucleoside antibiotics have been under investigation for many years (27). Some of the most clinically effective antiviral agents currently in use are purine or pyrimidine nucleoside analogs (24). For example, ribavirin, a synthetic nucleoside similar in structure to guanosine and inosine, has potent in vitro activity against a broad spectrum of viruses, including the epidemic respiratory viruses (3,25). Two effective inhibitors of bacteria are 9-,B-D-arabinofuranosyladenine and 2',3'-dideoxyadenosine. reported the lethality of the former to a purinerequiring strain of Escherichia coli B. In this organism, 9-4-D-arabinofuranosyladenine markedly inhibited DNA synthesis and had virtually no effect upon RNA synthesis. In addition, 2',3'-dideoxyadenosine was shown to be lethal to selected strains of E. coli by irreversibly inhibiting DNA synthesis in susceptible microorganisms (5, 28).As a result of screening synthetic compounds for potential antimicrobial activity, we have observed that compound BW A509U (3'-azido-3'-deoxythymidine, referred to as AZT in this paper; Fig. 1) has potent, bactericidal in vitro activity against various members of the family Enterobacteriaceae. This report describes the extent of the in vitro growthinhibiting activity of AZT and proposes a mechanism to explain its lethal properties. In addition, the antibacterial activity of AZT is discussed in light of the recent finding that this compound inhibits human T-cell lymphotropic virus type III/lymphadenopathy-assoc...

The molecular weight of dihydrofolate re-.

By the use of molecular models of Escherichia coli dihydrofolate reductase (DHFR), analogues of trimethoprim (TMP) were designed which incorporated various 3'-carboxyalkoxy moieties in order to acquire ionic interactions with positively charged active-site residues. Certain of these compounds have shown exceptionally high affinity for this enzyme. For example, the 3'-(carboxypentyl)oxy analogue was found to be 55-fold more inhibitory than TMP toward E. coli DHFR (Ki = 0.024 nM vs. 1.32 nM for TMP). X-ray crystallographic studies of E. coli DHFR in binary complexes with TMP and two members of this acid-containing series of compounds defined the binding of these inhibitors and showed the carboxyl group of the latter two inhibitors to be ionically bound to Arg-57. These observations were in agreement with postulated binding modes that were based on receptor modeling.

Forty trimethoprim analogues in which the para substituent in the benzene ring was varied were prepared for antibacterial evaluation. All were very potent inhibitors of Escherichia coli dihydrofolate reductase. The similarity of their inhibitory activities strongly suggested that the side chains beyond the first two atoms were not in contact with the enzyme. However, among 38 ether derivatives which varied widely in their bulk and lipophilicity, very few approached trimethoprim in their broad-spectrum in vitro antibacterial activity. The 4'-methyl and 4'-ethyl analogues and the allyloxy and gamma-chloropropoxy ethers had activities fairly close to that of trimethoprim. The two ethers were chosen for further evaluation in vivo. Neither compound quite matched trimethoprim in efficacy in mice, and their half-lives, as well as that of the beta-methoxyethoxy analogue, were found to be shorter in dogs.

The discovery of clonidine (1; Chart I) as a potent, centrally acting, hypotensive drug1-4 has led to detailed studies on the relationship between structure and hypotensive activity in the class of 2-(phenylimino)imidazolidines of the clonidine type. The majority of these investigations has considered variations of the substitution in the phenyl moiety of the molecules.