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L B Townsend

Publications and source records attributed to L B Townsend.

At least 73 records · Page 4Linked to original sources
PubMed1990

Synthesis and cytotoxicity studies of 8-amino-6-methyl-2-beta-D-ribofuranosyl-1,2,3,5,6,7-hexaazaacenaphthyle ne (7-aza-TCN) and the corresponding 2'-deoxy- and arabinonucleoside analogues.

The tricyclic nucleoside 8-amino-6-N-methyl-2-beta-D-ribofuranosyl-1,2,3,5,6, 7-hexaazaacenaphthylene was synthesized from 8-amino-6-N-methyl-4-(methylthio)-2-beta-D-ribofuranosyl-1,2,3,5,6, 7-hexaazaacenaphthylene. The 2'-deoxy analogue of 5, 8-amino-6-N-methyl-2-(2-deoxy-beta-D-ribofuranosyl)-1,2,3,5,6, 7-hexaazaacenaphthylene (11), and the arabino analogue of (5), 8-amino-6-N-methyl-2-beta-D-arabinofuranosyl-1,2,3,5,6, 7-hexaazaacenaphthylene (14) were synthesized from 5. Nucleosides 2,3,4,5,11, and 14 were evaluated for potential anticancer activity by measuring their ability to inhibit the growth of L1210 and H. Ep. 2 tumor cells in vitro.

Acenaphthenes↗
PubMed1989

Identification of 6-azauridine triphosphate in L1210 cells and its possible relevance to cytotoxicity.

L1210 cells treated with 1 mM 6-azauridine (AzUrd) (concentration causing 50% inhibition of cell growth, 3 microM) continued to divide at a reduced rate for 72 h before stopping. However, a 24-h treatment was lethal to 99% of the cells, as determined by colony formation. To investigate the mechanism for this delayed cytotoxicity, the metabolism of AzUrd was studied. Cells incubated with AzUrd contained a new 254 nm-absorbing component, not found in control cells. It appeared to be 6-azauridine-5'-triphosphate, since it was the only peak in the triphosphate region of the chromatogram which contained 3H after incubation of cells with [3H]AzUrd. Incorporation of [3H]AzUrd into the acid-insoluble fraction (nucleic acids) was also detected. A role for this incorporation in the mechanism of AzUrd cytotoxicity was strongly suggested by the observation that cordycepin (0.01 mM) partially protected cells from the lethality of AzUrd, presumably by preventing its incorporation into RNA. The previously known inhibition of pyrimidine de novo synthesis by AzUrd was confirmed by a decrease in the intracellular contents of UTP and CTP in AzUrd-treated cells. Therefore, we propose that the inhibition of pyrimidine de novo synthesis and the incorporation into nucleic acid(s) may act in concert to produce the cytotoxic effects of AzUrd.

Animals↗
PubMed1989

Low nanogram detection of nucleotides using fast atom bombardment-mass spectrometry.

The effect of trimethylsilyl (TMS) derivatization on detection limits of mononucleotides in fast atom bombardment-mass spectrometry (FAB-MS) was examined. FAB-MS methods were developed to optimize sensitivity using adenosine 5'-monophosphate as a model compound and then applied to reference standards of two clinically important nucleotides: tricyclic nucleoside-5'-monophosphate (TCNMP) and 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP). The detection limit for the TMS derivative of TCNMP was 2.5-5 ng/microliters and less than 2.5 ng/microliters for FdUMP as its TMS derivative. This is greater than two orders of magnitude more sensitive than the FAB-MS analysis of the corresponding free compounds. These low detection limits for the TMS derivatives were obtained using a narrow scan range, signal averaging, detection in the negative ion mode, and 3-nitrobenzyl alcohol as the matrix. Hydrolysis of one or more of the labile TMS groups did occur, with the extent of hydrolysis being greatest in the more protic matrices.

Gas Chromatography-Mass Spectrometry↗
PubMed1989

Synthesis, cytotoxicity, and antiviral activity of some acyclic analogues of the pyrrolo[2,3-d]pyrimidine nucleoside antibiotics tubercidin, toyocamycin, and sangivamycin.

A number of 7-[(1,3-dihydroxy-2-propoxy)methyl]pyrrolo[2,3d-d]pyrimidine derivatives that are structurally related to toyocamycin and sangivamycin and the seco nucleosides of tubercidin, toyocamycin, and sangivamycin were prepared and tested for their biological activity. Treatment of the sodium salt of 4-amino-6-bromo-5-cyanopyrrolo[2,3-d]-pyrimidine with 1,3-bis(benzyloxy)-2-propoxymethyl chloride afforded compound 3, which without isolation was debrominated to obtain 4-amino-5-cyano-7-[[1,3-bis(benzyloxy)-2- propoxy]methyl]pyrrolo[2,3-d]pyrimidine. Although catalytic hydrogenolysis failed, the benzyl ether functionalities of 4 were successfully cleaved by boron trichloride to afford 4-amino-5-cyano-7-[(1,3-dihydroxy-2- propoxy)methyl]pyrrolo[2,3-d]pyrimidine. Conventional functional group transformation of the cyano group of 6 provided a number of novel 5-substituted derivatives. Tubercidin (8a), toyocamycin (8b), and sangivamycin (8c) were treated separately with sodium metaperiodate and then with sodium borohydride to afford the 2',3'-seco derivatives 9a-c, respectively. The acyclic nucleoside 4-chloro-2-(methylthio)-7-[[1,3-bis(benzyloxy)-2- propoxy]methyl]pyrrolo[2,3-d]pyrimidine was aminated, desulfurized with Raney Ni, and then debenzylated to provide the tubercidin analogue 11. Cytotoxicity evaluation against L1210 murine leukemic cells in vitro showed that although the parent compounds tubercidin (8a), toyocamycin (8b), and sangivamycin (8c) were very potent growth inhibitors, the acyclic derivatives 6, 7a-c, and 9a-c had only slight growth-inhibitory activity. Evaluation of compounds 6, 7a, 7b, 7c, 9a, 9b, 9c, 11 for cytoxicity and activity against human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1) revealed that only the carboxamide (7a) and the thioamide (7c) were active. Compound 7c was the more potent of the two, inhibiting HCMV but not HSV-1 at concentrations producing little cytotoxicity.

Aminoglycosides↗
PubMed1989

Synthesis, cytotoxicity, and antiviral activity of certain 7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine nucleosides related to toyocamycin and sangivamycin.

A number of 7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine derivatives related to the nucleoside antibiotics toyocamycin and sangivamycin were prepared and tested for their biological activity. Treatment of the sodium salt of 4-amino-6-bromo-5-cyanopyrrolo[2,3-d]pyrimidine (1) with (2-acetoxyethoxy)methyl bromide (2) afforded a mixture of 4-amino-6-bromo-5-cyano-7-[(2-acetoxyethoxy)methyl]pyrrolo[2,3-d] pyrimidine (3) and the corresponding N1 isomer. Debromination of this mixture gave the corresponding 4-amino-5-cyano-7-[(2-acetoxyethoxy)-methyl]pyrrolo[2,3-d]pyrimidi ne (4) and 4-amino-5-cyano-1-[(2-acetoxyethoxy)methyl]pyrrolo[2,3-d]pyrimidin e (5). Deacetylation of 4 and 5 furnished 4-amino-5-cyano-7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine (6) and the corresponding N1 isomer (7), respectively. The sites of attachment for the acyclic moiety for 6 and 7 were assigned on the basis of UV spectral studies as well as 13C NMR spectroscopy. Conventional functional group transformation of 6 provided a number of novel 5-substituted derivatives (8-10), including the sangivamycin derivative 8. The methyl formimidate derivative 10 was converted to the thioamide derivative 11 and the carbohydrazide derivative 12. Compounds 6 and 8-12 were tested for cytotoxicity to L1210 murine leukemic cells in vitro. None of these compounds caused significant inhibition of cell growth. Evaluation of compounds 4 and 6-12 for activity against human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1) revealed that only the thioamide (11) was active. It inhibited HCMV but not HSV-1 at concentrations producing only slight cytotoxicity in human foreskin fibroblasts (HFF cells) and KB cells.

Aminoglycosides↗
PubMed1989

Antagonism of the cytotoxic but not antiviral effects of ara-sangivamycin by adenosine.

Inhibition of DNA synthesis by ara-sangivamycin was antagonized by adenosine. The 50% inhibitory concentrations increased 1.6- to 32-fold in the presence of 1.0 to 50 microM adenosine, respectively. In contrast, the inhibition of human cytomegalovirus replication by ara-sangivamycin was not antagonized by as much as 50 microM adenosine. This suggests that different enzymes were responsible for the phosphorylation of ara-sangivamycin in uninfected and infected cells.

Adenosine↗
PubMed1988

A rapid and sensitive screening method for the detection of anti-2-acetylaminofluorene immunoglobulins.

A method is described in which anti-2-acetylaminofluorene immunoglobulins may be detected using a simple and sensitive screening procedure. The method is based on immunoglobulin binding of an 125I derivatized 2-aminofluorene radiotracer. Tracer binding is not isotype specific, and thus the method is useful for the detection of either IgG or IgA. Competitive binding experiments with the radiotracer were used to determine the specificity of immunoglobulin response by measurement of cross-reactivity with related ligands. This method allows quantitation of the immune response to the carcinogen in serum and other biological fluids (i.e., intestinal secretions).

2-Acetylaminofluorene↗
PubMed1988

Synthesis and antiviral activity of certain 4- and 4,5-disubstituted 7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidines.

In vitro evaluation of a series of previously prepared tubercidin analogues revealed that certain 5-halogen-substituted analogues were active against human cytomegalovirus (HCMV) at concentrations lower than those that produced comparable cytotoxicity in uninfected cells. In contrast, tubercidin was cytotoxic at all antiviral concentrations. Even though the antiviral selectivity of the 5-substituted compounds was slight, this observation led us to prepare a series of acyclic analogues. Treatment of the sodium salt of 4-chloropyrrolo[2,3-d]pyrimidine (2) with (2-acetoxyethoxy)methyl bromide (2a) provided the acyclic nucleoside 4-chloro-7-[(2-acetoxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine (3). A nucleophilic displacement of the 4-chloro group with methoxide, methylamine, and dimethylamine yielded the corresponding 4-substituted compounds 4, 5, and 6, respectively, in good yield. Electrophilic substitution (chlorination, bromination, and iodination) was effected at the C-5 position of compound 3 with N-chlorosuccinimide, N-bromosuccinimide, and iodine monochloride, respectively, in methylene chloride. Removal of the acetyl group from these intermediates (7a-9a) with methanolic ammonia at room temperature afforded the 5-chloro (7b), 5-bromo (8b), and 5-iodo (9b) derivatives of 4-chloro-7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine. Treatment of compounds 7b-9b with methanolic ammonia at an elevated temperature produced the corresponding 5-halotubercidin analogues 10, 11, and 12, respectively. An alternate procedure for the preparation of these 4,5-disubstituted 7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidines involved an electrophilic substitution prior to the condensation of the heterocycle with 2a. Treatment of 2 with N-chlorosuccinimide and N-bromosuccinimide gave compounds 13a and 13b, respectively. The condensation of 13a and 13b with 2a and subsequent treatment with methylamine and ethylamine furnished the corresponding 5-halo-4-substituted-pyrrolo[2,3-d]pyrimidines 14a, 14b, 14c, and 14d, respectively. Evaluation of the target compounds (4-6, 7b-9b, 10-12, and 14a-14d) for cytotoxicity and activity against HCMV and herpes simplex virus type 1 (HSV-1) revealed that all compounds except the 5-halogen-substituted compounds 10, 11, and 12 were inactive. Compounds 10, 11, and 12 were active against both viruses at noncytotoxic concentrations. The activity of compound 11 was particularly noteworthy, being at least 10-fold more potent than acyclovir.

Acyclovir↗
PubMed1988

Synthesis and antiviral activity of certain 4-substituted and 2,4-disubstituted 7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidines.

Treatment of the sodium salt of 4-chloro-2-(methylthio)pyrrolo[2,3-d]pyrimidine (2) with (2-acetoxyethoxy)methyl bromide (3) has provided 4-chloro-2-(methylthio)-7[(2-acetoxyethoxy)methyl]pyrrolo[2,3- d]pyrimidine (4). Ammonolysis of 4 at room temperature gave 4-chloro-2-(methylthio)-7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3- d]pyrimidine (5). However, ammonolysis of 5 at 130 degrees C furnished 4-amino-2-(methylthio)-7-[(2-hydroxyethoxy)methyl]-pyrrolo[2,3- d]pyrimidine (6), which on desulfurization with Raney Ni yielded 4-amino-7-[(2-hydroxyethoxy)-methyl]pyrrolo[2,3-d]pyrimidine (7) (acyclic analogue of tubercidin). The oxidation of 6 with m-chloroperbenzoic acid provided the sulfone derivative 8. A nucleophilic displacement of the 2-methylsulfonyl group from 8 with methoxide anion provided 4-amino-2-methoxy-7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine (9). Demethylation of 9 with iodotrimethylsilane gave 4-amino-2-hydroxy-7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine (10). Treatment of 2,4-dichloropyrrolo[2,3-d]pyrimidine (11) with 3 gave the protected acyclic compound 12, which on deacetylation and ammonolysis under controlled reaction conditions gave 2,4-dichloro-7-[(2-hydroxyethoxy)-methyl]pyrrolo[2,3-d]pyrimidine (13) and 4-amino-2-chloro-7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3- d]pyrimidine (14), respectively. The condensation of 2-acetamido-4-chloropyrrolo[2,3-d]pyrimidine (15) with 3 gave the protected acyclic compound 16, which on concomitant deacetylation and ammonolysis with methanolic ammonia at an elevated temperature yielded 2,4-diamino-7-[(2-hydroxyethoxy)methyl]pyrrolo[2,3-d]pyrimidine (17) in moderate yield. In tests involving human cytomegalovirus (HCMV) and herpes simplex virus type 1 (HSV-1), only slight activity and cytotoxicity were observed. The most active compounds (12 and 13) were slightly more active against HCMV than acyclovir, but both compounds were inactive against HSV-1. The activity against HCMV, however, was not well separated from cytotoxicity leading to the conclusion that these compounds did not merit further study.

Animals↗
PubMed1987

Pyrrolo[2,3-d]pyrimidine nucleosides as inhibitors of human cytomegalovirus.

Seven arabinosyl, 2'-deoxyribosyl, and ribosyl pyrrolo[2,3-d]pyrimidines were evaluated in vitro for activity against human cytomegalovirus and for cytotoxicity in primary and established cell lines of human origin. The parent ribosyl analogs exhibited little antiviral selectivity owing to high cytotoxicity. In contrast, ara-tubercidin, ara-toyocamycin, ara-sangivamycin, and deoxysangivamycin exhibited selectivity between antiviral effect (measured by plaque or titer reduction or both) and cytotoxicity (measured microscopically and by incorporation of radioactive precursors into DNA, RNA, and protein). The selectivity (in vitro therapeutic indexes) for these four compounds ranged from 2 to 40. The two sangivamycin analogs were the most potent and selective. Ara-sangivamycin, for example, inhibited virus replication 10(5)-fold at a concentration (10 microM) which produced only partial inhibition of cell growth and labeled precursor incorporation. The four arabinosyl and deoxyribosyl nucleosides appeared to act by inhibition of viral DNA synthesis as quantitated by DNA-DNA dot blot hybridization. These four analogs also were tested for activity against two strains of type 1 herpes simplex virus by a plaque reduction assay. Unexpectedly, all compounds inhibited herpes simplex virus to a lesser extent than human cytomegalovirus.

Animals↗
PubMed1986

Expression of human malaria parasite purine nucleoside phosphorylase in host enzyme-deficient erythrocyte culture. Enzyme characterization and identification of novel inhibitors.

The intraerythrocytic human malaria parasite, Plasmodium falciparum, requires a source of hypoxanthine for nucleic acid synthesis and energy metabolism. Adenosine has been implicated as a major source for intraerythrocytic hypoxanthine production via deamination and phosphorolysis, utilizing adenosine deaminase and purine nucleoside phosphorylase, respectively. To study the expression and characteristics of human malaria purine nucleoside phosphorylase, P. falciparum was successfully cultured in purine nucleoside phosphorylase-deficient human erythrocytes to an 8% parasitemia level. Purine nucleoside phosphorylase activity was undetectable in the uninfected enzyme-deficient host red cells but after parasite infection rose to 1.5% of normal erythrocyte levels. The parasite purine nucleoside phosphorylase was not cross-reactive with antibody against human enzyme, exhibited a calculated native molecular weight of 147,000, and showed a single major electrophoretic form of pI 5.4 and substrate specificity for inosine, guanosine and deoxyguanosine but not xanthosine or adenosine. The Km values for substrates, inosine and guanosine, were 4-fold lower than that for the human erythrocyte enzyme. In these studies we have identified two novel potent inhibitors of both human erythrocyte and parasite purine nucleoside phosphorylase, 8-amino-5'-deoxy-5'-chloroguanosine and 8-amino-9-benzylguanine. These enzyme inhibitors may have some antimalarial potential by limiting hypoxanthine production in the parasite-infected erythrocyte.

Animals↗
PubMed1986

Potentiation of 2'-deoxyguanosine cytotoxicity by a novel inhibitor of purine nucleoside phosphorylase, 8-amino-9-benzylguanine.

We have synthesized and evaluated a series of 9-substituted analogues of 8-aminoguanine, a known inhibitor of human purine nucleoside phosphorylase (PNP) activity. The ability of these agents to inhibit PNP has been investigated. All compounds were found to act as competitive (with inosine) inhibitors of PNP, with Ki values ranging from 0.2 to 290 microM. The most potent of these analogues, 8-amino-9-benzylguanine; exhibited a Ki value that was 4-fold lower than that determined for the parent base, 8-aminoguanine. As a metabolically stable compound in human blood, 8-amino-9-benzylguanine was more effective than 8-aminoguanine at potentiating the toxicity of 2'-deoxyguanosine to MOLT-4 T-lymphoblasts in culture. 8-Amino-9-benzylguanine is the most potent base or nucleoside inhibitor of human PNP reported to date, and it is a promising lead compound in the development of more effective PNP inhibitors.

Antimetabolites, Antineoplastic↗
PubMed1986

The synthesis and biological activity of certain pentaazaacenaphthylenes, hexaazaacenaphthylenes and their corresponding nucleosides.

Synthesis of the tricyclic nucleoside 8-amino-6-N-methyl-2-(beta-D-ribo-furanosyl)-1,2,3,5,6,7-hexaazaacena phthylene (5) has been accomplished by the ring closure of an appropriately substituted pyrazolo[3,4-d]-pyrimidine nucleoside followed by the requisite chemical conversions. The formation, isolation and structural elucidation of two unexpected nucleosides formed by a reductive ring cleavage of the hexaazaacenaphthylene ring system is discussed. A comparison of the antitumor and biological activity of 5 with the structurally related tricyclic pentaazaacenaphthylene nucleoside which is currently in phase II clinical trials at the 5'-phosphate pro-drug is also presented.

Acenaphthenes↗
PubMed1986

Mechanism of activation of triciribine phosphate (TCN-P) as a prodrug form of TCN.

The tricyclic nucleotide triciribine phosphate (TCN-P) was synthesized as a water-soluble derivative of the tricyclic nucleoside TCN (L. B. Townsend et al, INSERM 81:37, 1978). Growth of L1210 cells in vitro was inhibited equally by TCN and TCN-P. A requirement for adenosine kinase activity for activation of both TCN and TCN-P was established by the observation that growth inhibition by either compound was decreased 200-fold by the adenosine kinase inhibitor 5-iodotubercidin and greater than 5000-fold in L1210/T, an adenosine kinase-deficient subline. The TCN/TCN-P resistance of L1210/T cells was correlated with lack of formation of intracellular TCN-P from either TCN or TCN-P. Thus, it appeared that TCN-P was hydrolyzed to TCN and then rephosphorylated intracellularly. Both the horse serum-containing culture medium and the intact cells possessed nucleotide phosphatase activity, which may contribute to the hydrolysis of TCN-P to TCN in the L1210 cell cultures. The requirement for hydrolysis of TCN-P to TCN for formation of intracellular TCN-P from exogenous TCN-P was also shown directly by the observation that human erythrocytes, which lack ectophosphatases, readily formed intracellular TCN-P from TCN but not from TCN-P when incubated in buffer.

Acenaphthenes↗
PubMed1985

Synthesis and biological activity of a novel adenosine analogue, 3-beta-D-ribofuranosylthieno[2,3-d]pyrimidin-4-one.

The title nucleoside 5 was prepared by a condensation of the silylated heterocycle thieno[2,3-d]pyrimidin-4-one (1) with 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranose (2a) in the presence of a Lewis acid or with 2,3,5-tri-O-acetyl-D-ribofuranosyl bromide (2b) in the presence of mercuric oxide and mercuric bromide. The site of ribosylation and anomeric configuration of this nucleoside were established by 1H NMR. The synthesis of 3-beta-D-ribofuranosylpyrrolo[2,3-d]pyrimidin-4-one (8), 1-phenyl-5-beta-D-ribofuranosylpyrazolo[3,4-d]pyrimidin-4-one (9), 5-methyl-3-beta-D-ribofuranosylthieno[2,3-d]pyrimidin-4-one (10), and 2-methyl-6-beta-D-ribofuranosyltriazolo[5,4-d]pyrimidin-7-one (11) is also described. The title compound inhibited the growth of murine L-1210 leukemic cells in vitro with an ID50 of 3 X 10(-5)M. The growth inhibition could not be prevented by uridine, cytidine, thymidine, deoxycytidine, cytosine, hypoxanthine, or uridine and hypoxanthine together. On the other hand, inhibition of adenosine kinase by 10(-7) M 5-iodotubercidin prevented the cytotoxic effect. Also a subline of L-1210 cells resistant to several cytotoxic adenosine analogues was also resistant to this nucleoside. Thus it appears that this compound 5 may act as an adenosine analogue.

Adenosine↗
PubMed1985

Effects of the tricyclic nucleoside 6-amino-4-methyl-8-(beta-D-ribofuranosyl)- pyrrolo[4,3,2-de]pyrimido[4,5-c]pyridazine on the viability and cell cycle distribution of L1210 cells in vitro.

TCN (1 microM) totally inhibited the growth of L1210 cells in culture and caused progressive loss of cellular viability, as indicated by a decreased clonogenicity and nigrosin dye exclusion. After 24 h or more of TCN treatment, a significant fraction of the cells had shrunk in size but did not fragment into dye-impermeable vesicles as reported previously for N1S1-67 hepatoma cells (P. G. W. Plagemann, J. Natl. Cancer Inst., 57: 1283-1295, 1976). TCN-induced growth inhibition was accompanied by a block of cell cycle progression in G1 or at the G1-S boundary. At all TCN concentrations studied, progression of cells out from behind this block was evident as a depletion of the early S-phase population in comparison to controls, while increasing the concentration of TCN (0.1 to 1 microM) led to a progressive retention of cells in S phase, suggesting a slowing of progression through S phase. The fraction of S-phase cells incorporating [methyl-3H]thymidine and the amount of [methyl-3H]thymidine incorporated per labeled cell were both decreased by TCN treatment. Increasing the concentration of TCN (0.1 to 1 microM) progressively decreased DNA synthesis and increased cell lethality. Thus it appeared that inhibition of DNA synthesis might cause the retention of cells in S phase which is associated with TCN lethality.

Animals↗