The thymidine analog 3'-azido-3'-deoxythymidine (BW A509U, azidothymidine) can inhibit human immunodeficiency virus (HIV) replication effectively in the 50-500 nM range [Mitsuya, H., Weinhold, K. J., Furman, P. A., St. Clair, M. H., Nusinoff-Lehrman, S., Gallo, R. C., Bolognesi, D., Barry, D. W. & Broder, S. (1985) Proc. Naul. Acad. Sci. USA 82,[7096][7097][7098][7099][7100]. In contrast, inhibition of the growth of uninfected human fibroblasts and lymphocytes has been observed only at concentrations above 1 mM. The nature of this selectivity was investigated. Azidothymidine anabolism to the 5'-mono-, -di-, and -triphosphate derivatives was similar in uninfected and HIV-infected cells. The level of azidothymidine monophosphate was high, whereas the levels of the di-and triphosphate were low (c5 MuM and <2 MuM, respectively).Cytosolic thymidine kinase (EC 2.7.1.21) was responsible for phosphorylation of azidothymidine to its monophosphate. Purified thymidine kinase catalyzed the phosphorylations of thymidine and azidothymidine with apparent K. values of 2.9MuM and 3.0 ,uM. The maximal rate of phosphorylation with azidothymidine was equal to 60% of the rate with thymidine. Phosphorylation of azidothymidine monophosphate to the diphosphate also appeared to be catalyzed by a host-cell enzyme, thymidylate kinase (EC 2.7.4.9). The apparent Km value for azidothymidine monophosphate was 2-fold greater than the value for dTMP (8.6 ,uM vs. 4.1 MM), but the maximal phosphorylation rate was only 0.3% of the dTMP rate. These kinetic constants were consistent with the anabolism results and indicated that azidothymidine monophosphate is an alternative-substrate inhibitor of thymidylate kinase. This conclusion was reflected in the observation that cells incubated with azidothymidine had reduced intracellular levels of dTTP. ICso (concentration of inhibitor that inhibits enzyme activity 50%) values were determined for azidothymidine triphosphate with HYIV reverse transcriptase and with immortalized human lymphocyte (H9 cell) DNA polymerase a. Azidothymidine triphosphate competed about 100-fold better for the HIV reverse transcriptase than for the cellular DNA polymerase a. The results reported here suggest that azidothymidine is nonselectively phosphorylated but that the triphosphate derivative efficiently and selectively binds to the HIV reverse transcriptase. Incorporation of azidothymidylate into a growing DNA strand should terminate DNA elongation and thus inhibit DNA synthesis.

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 volatile flavour components of 27 Allium species and cultivars, mostly edible but including some decorative species for comparison, have been investigated by a series of gas and thin-layer chromatographic and U.V. spectrophotometric methods. By means of simulation experiments with synthetic precursors and intermediates, the data have been interpreted in terms of the amino acid precursors present in the intact tissues and the species classified as containing (a) S-1-propenyl-, (b) S-2-propenyl-and (c) S-methyl-L-cysteine sulphoxides as their principal flavour precursors. Characteristic examples of the three types are A . cepa L. (onion), A . sativum L. (garlic) and A . aflatunense B. Fedtschenko,respectively. An object of the work has been to demonstrate broad chemical similarities between species as well as their differences, which are emphasised in keys for classification on the basis of morphological characters. In addition to onion, leek, shallot, garlic and chives, species such as A. chinense, A . Jistulosum and A . tuberosum have widespread use as food, particularly in the Far East. The literature on this aspect has been briefly summarised.

A series of 2'-deoxy-4'-thioribo purine nucleosides was prepared by trans-N-deoxyribosylase-catalyzed reaction of 2'-deoxy-4'-thiouridine with a variety of purine bases. This synthetic procedure is an improvement over methods previously used to prepare purine 4'-thio nucleosides. The compounds were tested against hepatitis B virus (HBV), human cytomegalovirus (HCMV), herpes simplex virus (HSV-1 and HSV-2), varicella zoster virus (VZV), and human immunodeficiency virus (HIV-1). Cytotoxicity was determined in a number of cell lines. Several compounds were extremely potent against HBV and HCMV and had moderate to severe cytotoxicity in vitro. The lead compound from the series, 2-amino-6-(cyclopropylamino)purine 2'-deoxy-4'-thioriboside, was the most potent and selective agent against HCMV and HBV replication in vitro; however, this analogue was nephrotoxic when tested in vivo.

It is known that the volatile components of raw and cooked onions contain mono-, di-and tri-sulphides and other flavour-contributing sulphur compounds. The relationship between the sulphate nutrition of spring (salad) onion (Allium cepa) and its flavour strength determined by sensory, biochemical and chromatographic methods has been investigated. The plants were grown in sand culture in a glasshouse and the nutrient solutions contained five levels of sulphate from zero to an adequate amount. In their growth response, total sulphur content and visual symptoms, the plants showed characteristic essential nutrient deficiency. The sensory tests, and instrumental and biochemical assays showed that flavour strength increased approximately in proportion to sulphate concentration in the medium; lachrymatory potency also increased. There were signscant coefficients of correlation between sulphate concentration of the nutrient medium and some aspects of flavour strength. The correlation coefficients between total sulphur content (% of the edible portion) and total peak area, n-propyl disulphide peak area and total pyruvate were also high. These observations suggest the possibility of control of onion flavour strength and lachrymatory potency, under field conditions, by control of sulphate nutrition. The question of loss of maximum potential onion flavour as a consequence of sulphur deficiency in soils is discussed.A headspace method for sampling onion flavour volatiles and for their introduction into gas chromatographs is described.