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L B Townsend

Publications and source records attributed to L B Townsend.

At least 55 records · Page 3Linked to original sources
PubMed1994

Relationship between cytotoxicity and conversion of thiosangivamycin analogs to toyocamycin analogs in cell culture medium.

Non-nucleoside analogs of the pyrrolopyrimidine nucleosides toyocamycin, sangivamycin and thiosangivamycin have been synthesized and their cytotoxicity in mammalian cells determined. While studying the effects of 5-thioamide-substituted analogs on cell growth, we observed an interesting phenomenon in which cells recovered spontaneously from growth inhibition during extended incubations. HPLC studies demonstrated that the 5-thioamide moiety of several structurally dissimilar 7-substituted 4-aminopyrrolo[2,3-d]pyrimidines, including thiosangivamycin, is unstable in cell culture medium and is converted to the corresponding 5-nitrile with a half-life of approximately 48 h. In contrast, different substituents at the 4-position of the heterocycle significantly affected the stability of the 5-thioamide moiety. Conversion of the thioamide to the nitrile was caused by components in the cell culture medium, not components of serum. The above observations demonstrate that caution should be exercised in interpreting biological data obtained in vitro for 5-thioamide pyrrolo[2,3-d]pyrimidines.

Antibiotics, Antineoplastic↗
PubMed1993

Synthesis, antiproliferative, and antiviral activity of 4-amino-1-(beta-D-ribofuranosyl)pyrrolo[2,3-d]pyridazin-7(6H)-one and related derivatives.

The synthesis of 4-amino-1-beta-D-ribofuranosylpyrrolo[2,3-d]pyridazin-7 (6H)-one (3) from the reaction of ethyl 3-cyano-1-beta-D-ribofuranosylpyrrole-2-carboxylate (10) and hydrazine is described. The 5:6 pyrrolo[2,3-d]pyridazin-7(6H)-one structure of 3 was established via a three-step conversion of 3 into 1-beta-D-ribofuranosylpyrrolo[2,3-d]pyridazin-4,7(5H,6H)- dio ne (14). 4-Amino-3-chloro-1-beta-D-ribofuranosylpyrrolo[2,3-d]pyridazin+ ++-7(6H)-one (16) 4-amino-3-bromo-1-beta-D-ribofuranosylpyrrolo[2,3-d]pyridazin++ +-7(6H)-one (18) were prepared via N-chlorosuccinimide or N-bromosuccinimide treatment of 4-amino-1-(2,3,5-tri-O-benzyl-beta- D-ribofuranosyl)pyrrolo[2,3-d]pyridazin-7(6H)-one (7) followed by a removal of the benzyl groups with boron trichloride. Direct treatment of 3 with N-iodosuccinimide furnished 4-amino-3-iodo-1-beta-D-ribofuranosylpyrrolo[2,3-d]pyridazin -7(6H)-one (19). The antiproliferative activity of the compounds was determined in L1210, H. Ep. 2 and several additional human tumor cell lines. In L1210 cells, the 3-halo-substituted compounds 16, 18, and 19 exhibited significant cytotoxicity (IC50 = 0.2, 0.1, 0.08 microM, respectively), in contrast to the 3-unsubstituted compound 3, which had only slight activity. The greater antiproliferative activity of 18 and 19 in contrast to 3 was confirmed in H. Ep. 2 cells and KB cells. The antiviral evaluation of these compounds revealed that compounds 16, 18, and 19 were active against human cytomegalovirus in both plaque- and yield-reduction assays. However, this activity was only partially separated from cytotoxicity in human cell lines.

Animals↗
PubMed1993

Synthesis of 2,4-disubstituted thiazoles and selenazoles as potential antitumor and antifilarial agents: 1. Methyl 4-(isothiocyanatomethyl)thiazole-2-carbamates, -selenazole-2- carbamates, and related derivatives.

Methyl 4-(isothiocyanatomethyl)thiazole-2-carbamate and methyl 4-(isothiocyanatomethyl)selenazole-2-carbamate have been prepared via chemical transformations involving 2-amino-4-(chloromethyl)thiazole (1) and 2-amino-4-(chloromethyl)selenazole (2), respectively, as starting materials. The homoanalog, methyl 4-(2-isothiocyanatoethyl)thiazole-2-carbamate, was prepared from (2-aminothiazol-4-yl)acetic acid. All compounds prepared were evaluated for their ability to inhibit leukemia L1210 cell proliferation. Methyl 4-(isothiocyanatomethyl)thiazole-2-carbamate (7) was the most active compound in this screen, inhibiting the growth of L1210 leukemic cells with an IC50 = 3.2 microM. Mitotic blocking appears to be its primary mechanism of cytotoxic activity. Compound 7 also was the only compound which demonstrated significant in vivo antifilarial activity against the adult worms of Acanthocheilonema viteae in experimentally infected jirds. This compound was inactive against Brugia pahangi at a dosage of 100 mg/kg x 5 days.

Animals↗
PubMed1993

Synthesis of 2,4-disubstituted thiazoles and selenazoles as potential antifilarial and antitumor agents. 2. 2-Arylamido and 2-alkylamido derivatives of 2-amino-4-(isothiocyanatomethyl)thiazole and 2-amino-4-(isothiocyanatomethyl)selenazole.

The synthesis of a series of 2-arylamido and 2-alkylamido derivatives of 2-amino-4-(isothiocyanatomethyl)thiazole and 2-amino-4-(isothiocyanatomethyl)selenazole is described. In vitro antiproliferative evaluations were carried out using L1210 cells. The 2-(alkylamido)thiazole derivatives were moderately antiproliferative, with IC50's of 4-8 microM. A significant increase in activity was obtained for the arylamido derivatives, with IC50's of 0.2-1 microM. The results obtained for the selenazoles were similar to those for the thiazoles. 2-Benzamido-4-(isothiocyanatomethyl)-thiazole (19) was found to be a potent inhibitor of GMP synthetase. None of the compounds prepared in this study demonstrated antifilarial activity.

Animals↗
PubMed1993

Nucleosides. 5. Synthesis of guanine and formycin B derivatives as potential inhibitors of purine nucleoside phosphorylase.

In an effort to develop potent human purine nucleoside phosphorylase (PNP) inhibitors as immunosuppressive and chemotherapeutic agents, several 8-aminoguanine derivatives were synthesized and evaluated as potential PNP inhibitors. These studies were designed to investigate the hydrophobic effect of a substituent on the N-9 of the purine heterocycle and/or the C-5' positions. Compounds such as 8-aminoguanosine, guanosine, formycin B, and 8-aminoacyclovir containing a p-(fluorosulfonyl)benzoyl moiety were synthesized. The affinity of these compounds to erythrocytic PNP was determined and none of these compounds showed a better affinity than those of the parent compounds. However, we found that the effect of hydrophobicity at the N-9 and the C-5' positions might play an important role in binding to the active site of PNP. Thus, 8-amino-5'-deoxy-5'-(phenylthio)guanosine (19) was found to be the best inhibitor in this series of compounds with a Ki = 0.45 microM.

Binding Sites↗
PubMed1992

Inhibition of adenosine deaminase by azapurine ribonucleosides.

We have synthesized several 8-azapurine nucleosides as inhibitors of adenosine deaminase. The presence of a nitrogen on the imidazole ring decreased the Ki value for nebularine by 100-fold but did not lower the Ki value for coformycin. Evaluation of these compounds in a MOLT-4 growth assay revealed that 2-azacoformycin was as effective as 2'-deoxycoformycin in potentiating growth inhibition by 2'-deoxyadenosine. The azapurine nucleosides merit further study as antitumor agents.

Adenosine Deaminase Inhibitors↗
PubMed1992

Improved synthesis and biological evaluation of an acyclic thiosangivamycin active against human cytomegalovirus.

We previously described the synthesis and in vitro antiviral activity of an acyclic thiosangivamycin analog (Gupta et al., 1989a). In order to extend these initial studies, a new, multi-gram synthesis of 4-amino-7-[(2-hydroxy- ethoxy)methyl]pyrrolo]2,3-d]pyrimidine-5-thiocarboxamide (compound 229) was achieved in 5 steps from the known 5-amino-2-bromo-3,4-dicyanopyrrole in good overall yield. In plaque reduction assays with HCMV, compound 229 had an IC50 of 7 microM; in yield reduction assays the IC90 was 25 microM. The compound was less active against MCMV, HSV-1, HSV-2, and least active against VZV. Concentrations of compound 229 up to 32 microM did not affect the growth of KB cells for incubation periods up to 72 h. At 100 microM, a prolongation in population doubling time from 21 h (untreated) to 35 h was noted. This inhibition, however, was reversible upon removal of the compound suggesting the inhibition was cytostatic rather than cytotoxic. Flow cytometric studies with compound 229 in HFF cells revealed an accumulation of cells in S phase and a concurrent loss of cells in G2/M phase, suggesting an early S phase blockage. We conclude there is adequate separation between antiviral activity and cytotoxicity to merit further work with this class of pyrrolopyrimidines.

Antiviral Agents↗
PubMed1992

Synthesis, antiproliferative, and antiviral activity of certain 4-aminopyrrolo[2,3-d]pyridazine nucleosides: an entry into a novel series of adenosine analogues.

The preparation of novel heterocyclic base modified adenosine analogues, the 4-aminopyrrolo[2,3-d]pyridazine nucleosides, is described. Crucial to their successful preparation was the use of the pyrrole glycoside intermediates 3-cyano-2-formyl-1-(2,3,5-tri-O-benzyl-beta-D-ribofuranosyl)pyrrole (11) and 3-cyano-2-formyl-1-(2,3,5-tri-O-benzyl-beta-D-arabinofuranosyl)pyrrole (17). Treatment of 11 and 17 with hydrazine dihydrochloride followed by treatment with boron trichloride provided 4-amino-1-beta-D-ribofuranosylpyrrolo[2,3-d]pyridazine (2) and 4-amino-1-beta-D-arabinofuranosylpyrrolo[2,3-d]pyridazine (3), respectively. 4-Amino-3-bromo-1-beta-D-ribofuranosylpyrrolo[2,3-d]-pyridazine (4) was prepared by a bromination of 4-amino-1-(2,3,5-tri-O-benzyl-beta-D-ribofuranosyl)pyrrolo[2,3-d]pyri daz ine (12) and subsequent removal of the benzyl groups with boron trichloride. Compounds 2-4 were evaluated for antiproliferative and antiviral activity. The tubercidin analogue (2) and its arabinosyl derivative (3) were virtually inactive in all assays. In contrast, the 3-bromo analogue 4 inhibited growth of L1210 and H. Ep. 2 cells. Compound 4 was also active against human cytomegalovirus and herpes simplex virus type 1, but the antiviral activity was not completely separated from cytotoxicity.

Adenosine↗
PubMed1992

Synthesis and biological activity of certain alkyl 5-(alkoxycarbonyl)-1H-benzimidazole-2-carbamates and related derivatives: a new class of potential antineoplastic and antifilarial agents.

A series of methyl and ethyl 5-(alkoxycarbonyl)-1H-benzimidazole-2-carbamates (7-19) and methyl 5-carbamoyl-1H-benzimidazole-2-carbamates (24-34) have been synthesized via the reaction of an appropriate alcohol or amine with the acid chloride derivatives 6a or 6b at room temperature. Reaction of an alcohol with acid chloride 6a at reflux temperature afforded transesterified products 20-23 in good yield. Treatment of methyl 5-amino-1H-benzimidazole-2-carbamate with substituted benzoyl chlorides furnished the methyl 5-benzamido-1H-benzimidazole-2-carbamates (36-38). Compounds 9, 16, 20, and 22 demonstrated significant growth inhibition in L1210 cells with IC50's less than 1 microM. Growth inhibition by this series of compounds appears to be associated with mitotic spindle poisoning. All the compounds tested, 9, 10, 19, 20, 22, and 23, caused significant accumulation of L1210 cells in mitosis. Compounds 7, 9, 19, 25, 26, 27, and 36 showed significant in vivo antifilarial activity against adult worms of Brugia pahangi, Litomosoides carinii, and Acanthocheilonema viteae in experimentally infected jirds.

Animals↗
PubMed1991

Activity of acyclic halogenated tubercidin analogs against human cytomegalovirus and in uninfected cells.

Novel acyclic halogenated tubercidins (4-amino-5-halo-7-[(2-hydroxyethoxy)-methyl]pyrrolo[2,3-d]pyrimidines) were examined for their ability to inhibit human cytomegalovirus (HCMV) in yield reduction assays. 5-Bromo acyclic tubercidin (compound 102) was a more potent inhibitor of virus replication than the chloro- and iodo-substituted analogs (compounds 100 and 104). At a 100 microM concentration, the bromo and chloro compounds were more potent than acyclovir but not ganciclovir. Virus titers were reduced more than 99% by compounds 102 and 104 whereas compound 100 and the equally potent acyclovir reduced titers by only 90%. Quantitation of viral DNA by DNA hybridization demonstrated strong inhibition of HCMV DNA synthesis by these compounds. The most potent inhibitor, compound 102, had a 50% inhibitory (I50) concentration (1.6 microM) comparable to that of ganciclovir (1.8 microM). Cytotoxicity in uninfected human cells was evaluated and revealed the following: cell growth rates slowed markedly in the presence of 10 microM compound 102 whereas the same concentration of compounds 100 and 104 led to only a slight prolongation of population doubling time; these compounds inhibited cellular DNA synthesis but not RNA or protein synthesis, as measured by incorporation of radiolabeled precursors into acid-precipitable macromolecules; flow cytometry indicated that compound 102 was a mid-S phase blocker, and adenosine antagonized the inhibition of [3H]dThd incorporation by compound 102. Together, these results demonstrate that compound 102 is a potent and selective inhibitor of viral and cellular DNA synthesis and that acyclic halogenated pyrrolo-pyrimidine nucleosides may have therapeutic potential.

Adenosine↗
PubMed1991

Synthetic approaches to the guanosine and xanthosine analogues 5-amino-3-beta-D-ribofuranosylpyrazolo[3,4-e][1,3]oxazin-7-one and 3-beta-D-ribofuranosylpyrazolo[3,4-e][1,3]oxazine-5,7-dione and studies of their antitumor potential.

5-Amino-3-beta-D-ribofuranosylpyrazolo[3,4-e][1,3]oxazin-7-o ne has been synthesized via cyclization of the appropriately protected pyrazofurin derivatives and subsequent transformations of the heterocyclic moiety. This guanosine analogue was marginally cytotoxic to L1210 cells in vitro. The xanthosine analogue 3-beta-D-ribofuranosylpyrazolo[3,4-e][1,3]oxazine-5,7-dione was also synthesized, and was found to be highly cytotoxic. It appeared to act as a prodrug of pyrazofurin.

Animals↗
PubMed1990

Dual mechanisms of inhibition of DNA synthesis by triciribine.

The inhibition of DNA synthesis in triciribine (TCN)-treated L1210 cells was shown to involve two mechanisms, with different concentration dependence. (a) Initiation of new replicons and possibly of Okazaki fragments was inhibited when the cells were treated with 0.1 microM TCN. The inhibition of replicon initiation was shown by the rate of alkaline elution of [3H]DNA from 15-min-[3H]thymidine-labeled cells being slower if the cells had been pretreated with TCN, indicating that the average size of actively replicating DNA strands was increased. (b) At 1 microM TCN elongation of previously initiated DNA chains was also inhibited. This conclusion was suggested by the decrease in the rate of alkaline elution of [3H]DNA, during postlabeling incubation, being less if TCN was included in the medium. The mechanism of inhibition of DNA synthesis by TCN was shown not to involve DNA strand breakage or cross-linking, inhibition of polyamine biosynthesis, inhibition of purine de novo biosynthesis, inhibition of DNA polymerase alpha or DNA primase, or inhibition of ligation of Okazaki fragments. The effects of TCN on the incorporation of [3H]thymidine into Okazaki fragments and higher molecular weight DNA suggested the possibilities of inhibition of Okazaki fragment initiation and/or DNA polymerase delta.

Animals↗
PubMed1990

Flow cytometric evaluation of the cytotoxicity of novel antiviral compounds.

Two acyclic analogs of bromotubercidin were tested for cytotoxic effects on uninfected cells by monitoring cell growth and measuring cell cycle perturbations using flow cytometry. As reported elsewhere, 5-bromotubercidin analogs in which ribose was replaced by 2-hydroxyethoxymethyl (compound 102) or by 1,3-dihydroxypropoxymethyl (compound 183) were potent inhibitors of human cytomegalovirus (HCMV) replication in vitro (Pudlo et al.: Journal of Medicinal Chemistry 31:2086-2092, 1988). Because these compounds also inhibited the growth of uninfected cells, we performed kinetic studies with an established neoplastic line of human cells (KB) using flow cytometry. Growth of KB cells treated with either compound 102 or 183 were inhibited in a dose-dependent manner. Growth inhibition by compound 183, however, was not fully expressed for at least 24 h. DNA analysis by flow cytometry showed that a 4-h incubation with 10 microM compound 102 caused a decrease of cells in G2/M phase. Cells began to accumulate in early S phase by 12 h of incubation, leading to mid S phase accumulation at 21 h. Compound 183 at 10 microM slightly decreased the number of cells in G2/M phase after a 4-h incubation, and led to accumulation of DNA in S phase after a 12-h incubation. By 24 and 30 h, DNA histograms appeared similar to those of control cells but with a slight accumulation of the population in early S phase. In separate experiments, drugs were removed following a 24-h incubation. After removal of compound 102, KB cell growth resumed with a normal population doubling time. In contrast, the effects of compound 183 were not reversible, suggesting the two compounds acted by different biochemical mechanisms.

Antiviral Agents↗
PubMed1990

The synthesis and chemistry of certain anthelmintic benzimidazoles.

A basis for interest in the benzimidazole ring system as a nucleus from which to develop potential chemotherapeutic agents was established in the 1950s when it was found that 5,6-dimethyl-l-(alpha-D-ribofuranosyl)benzimidazole (I) was an integral part of the [structure: see text] structure of vitamin B(12). As a result of these interests and extensive studies, one health related arena that has benefited greatly has been the treatment of parasitic diseases. The discovery of thiabendazole in 1961 further spurred chemists around the world to design and synthesize several thousand benzimidazoles for screening for anthelmintic activity but less than twenty of them have reached commercial use. Much of this work has been done by pharmaceutical companies and is only reported in the patent literature. In this paper, Leroy Townsend and Dean Wise review the development of some of the synthetic methods that have been critical to the preparation of the benzimidazoles of anthelmintic importance. Only a few molecules that demonstrate the processes are discussed here, but numerous reviews of the synthesis and chemistry of other benzimidazoles are available.

Journal Article↗
PubMed1990

Synthesis and antiviral activity of some 7-[(2-hydroxyethoxy)methyl]pyrazolo[3,4-d]pyrimidine analogues of sangivamycin and toyocamycin.

The sodium salt of 4-amino-3-cyanopyrazolo[3,4-d]pyrimidine (1) was condensed with (2-acetoxyethoxy)methyl bromide (2) to provide the corresponding protected acyclic nucleoside, 4-amino-3-cyano-1-[(2-acetoxyethoxy)methyl]-pyrazolo[3,4-d]pyrimid ine (3). Treatment of 3 with sodium methoxide in methanol provided a good yield of methyl 4-amino-1-[(2-hydroxyethoxy)methyl]pyrazolo[3,4-d]pyrimidine-3- formimidate (4). Treatment of the imidate (4) with sodium hydrogen sulfide gave the thiocarboxamide derivative 5. Aqueous base transformed 4 into 4-amino-1-[(2-hydroxyethoxy)methyl]pyrazolo[3,4-d]pyrimidine-3- carboxamide (6) in good yield. Treatment of 5 with mercuric chloride furnished the toyocamycin analogue 7. Evaluation of compounds 1, 3-7 revealed that only the heterocycle (1) and the thiocarboxamide acyclic nucleoside (5) were active. Compound 5 was the more potent with activity against human cytomegalovirus and herpes simplex virus type 1.

Aminoglycosides↗
PubMed1990

Synthesis, antiproliferative, and antiviral activity of certain 4-substituted and 4,5-disubstituted 7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3-d]pyrimidines.

The sodium salts of 4-chloro- and several 4-chloro-5-substituted-7H-pyrrolo[2,3-d]pyrimidines were treated with [1,3-bis(benzyloxy)-2-propoxy]methyl chloride (6) to provide the corresponding 4-chloro- and 4-chloro-5-substituted-7-[[1,3-bis(benzyloxy)-2-propoxy]methyl]pyrrolo [2,3-d]pyrimidines (7-11). Debenzylation with boron trichloride at -78 degrees C furnished 4-chloro- and several 4-chloro-5-substituted-7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3- d]pyrimidines (12.16). Subsequent amination of 12-16 yielded the 4-amino-5-substituted-7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3- d]pyrimidines (17-21). Treatment of 14 with methylamine and 13 and 14 with ethylamine yielded the 4-(alkylamino)-5-halo-7-[(1,3-dihydroxy-2- propoxy)methyl]pyrrolo[2,3-d]pyrimidines (22-24). Treatment of 12-15 with hydroxylamine in refluxing 2-propanol yielded the 5-substituted-4-(hydroxyamino)-7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrol o [2,3-d]pyrimidines (25-28). Treatment of compound 12 with Pd/C under a hydrogen atmosphere has furnished the nebularine analogue 31. The antiproliferative activity of compounds 17-28 and 31 was studied using L1210 cells in vitro. The 4-amino- and 4-(hydroxyamino)-5-halogenated derivatives (compounds 18-20, 26-28) inhibited cell growth. Although the effect of compounds 18-20 and 27 on final growth rate was pronounced (IC50 = 2.3, 0.7, 2.8, and 3.7 microM, respectively), cells underwent at least one doubling before cell division stopped. The remaining compounds were less cytotoxic, with IC50's greater than 30 microM for 21, 23, 26, and 28, whereas no inhibition of L1210 cell growth was observed with compounds 17, 22, 24, 25, and 31 at 100 microM. The antiviral activity of these compounds also was tested. Compounds 18-20 and 26-28 were active against human cytomegalovirus and herpes simplex type 1. The 4-amino derivatives (18-20) were more active than the 4-hydroxyamino derivatives (26-28), the 4-amino-5-bromo and 4-amino-5-iodo derivatives produced more than five log reductions in virus titer at concentrations of 10-100 microM. Although some cytotoxicity was observed at these concentrations, compound 19 was active against murine cytomegalovirus in vivo. At 5.6 mg/kg, 14/15 animals survived compared to 10/15 treated with 5.6 mg/kg of ganciclovir or 1/15 treated with placebo.

Animals↗
PubMed1990

Arabinofuranosylpyrrolo[2,3-d]pyrimidines as potential agents for human cytomegalovirus infections.

Protection of the 3'- and 5'-hydroxyl groups of the nucleoside antibiotic toyocamycin (1) with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane was followed by (trifluoromethyl)sulfonylation of the 2'-hydroxyl group. A displacement of the resulting triflate ester moiety with lithium chloride, lithium bromide, sodium iodide, and lithium azide in hexamethylphosphoramide was followed by a removal of the disilyl moiety with tetra-n-butylammonium fluoride to afford the appropriate (2'-deoxy-2'-substituted-arabinofuranosyl)toyocamycin analogues 6a-d. Hydrolysis of the carbonitrile moieties of 6a-d with hydrogen peroxide gave the corresponding sangivamycin analogues (7a-d). A reduction of the azido moiety of 6a and 7a with 1,3-propanedithiol furnished the corresponding amino derivatives (6e and 7e). The antiproliferative activity of 6a-e and 7a-e was evaluated in L1210 cell cultures. None of these compounds caused significant inhibition of cell growth. Evaluation of these compounds for antiviral activity showed that all the toyocamycin analogues were active against human CMV, but of the sangivamycin analogues, only (2'-deoxy-2'-azidoarabinosyl)sangivamycin (7a) was active against this virus. None of the compounds were active against HSV-1 or HSV-2. (2'-Deoxy-2'-aminoarabinofuranosyl)toyocamycin (6e) was studied more extensively and showed some separation between antiviral activity and cytotoxicity as measured by effects on DNA synthesis, cell growth, and cell-plating efficiency. Although 6e also was active against murine CMV in vitro, it was not active against this virus in infected mice. We conclude that arabinosylpyrrolopyrimidines have potential as antivirals, but no members of the current series are potent enough to show significant activity in vivo.

Animals↗