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R B Meyer

Publications and source records attributed to R B Meyer.

At least 37 records · Page 2Linked to original sources
PubMed1995

Structure-activity relationships of cytotoxic cholesterol-modified DNA duplexes.

Short DNA duplexes with cholesterol linked at the 3'-terminus of each strand have unique, selective cytotoxic properties. The structural requirements for biological activity were explored through chemical synthesis of analogs and testing in cultured hepatoma cells. Effects of modifications to the sequence, backbone, 3'-sterol, 3'-linker, and 5'-terminus were evaluated. Self-complementary 3'-modified oligodeoxynucleotide (ODN) 10-mers were prepared from solid supports bearing the modification and linker of interest. Any changes to the normal phosphodiester backbone were poorly tolerated. The presence of cholesterol or a closely related sterol was an absolute requirement for activity. The length and position of attachment of the linker to cholesterol was important, with longer linkers showing reduced activity. Large, lipophilic groups at the 5'-terminus gave reduced cytotoxicity and poor solubility properties. The short length and unique structure of these ODNs allowed efficient automated synthesis on a 400 mumol scale and simplified purification.

Antineoplastic Agents↗
PubMed1995

Sequence-specific covalent modification of DNA by cross-linking oligonucleotides. Catalysis by RecA and implication for the mechanism of synaptic joint formation.

Oligodeoxynucleotides (ODNs) were conjugated to chlorambucil and used as affinity labeling reagents to study joint molecule formation by the Escherichia coli recombinase recA. Chlorambucil is a bifunctional nitrogen mustard which alkylates the N-7 position of guanine in the major groove of double-stranded DNA (dsDNA). Incoming ODNs at least 30 nucleotides long cross-linked to a long homologous duplex DNA in the presence of recA and ATP gamma S. Efficient cross-linkage to the complementary recipient strand of the joint occurred preferentially at guanines positioned 5' relative to the appended chlorambucil group. The pattern of recipient strand alkylation was identical to that observed within a protein-free duplex and indicated that strand exchange had occurred prior to alkylation. Modification of the outgoing homologous strand of the joint was less efficient and spanned a 15-20 nucleotide long region offset to the 3' side of the tethered chlorambucil. Alkylation of both recipient and outgoing strands in the same joint molecule occurred with low frequency. By contrast, no affinity alkylation of the displaced strand was observed within a synthetic D-loop. These reaction patterns suggest that the incoming ODN approaches from the minor groove of the duplex to yield a poststrand exchange joint in which the major groove of the newly formed heteroduplex harbors the outgoing strand in an unpaired state. No evidence was obtained for the involvement of a triple-stranded DNA intermediate in recombination.

Affinity Labels↗
PubMed1994

Discovery of short, 3'-cholesterol-modified DNA duplexes with unique antitumor cell activity.

A new class of modified oligodeoxynucleotides with unique, selective cytotoxic properties has been discovered. Self-complementary, 3'-cholesterol-modified oligodeoxynucleotides caused morphology changes and death in certain cancer cell lines, whereas other cell lines were unaffected. Susceptible cells were killed in a dose-dependent manner at submicromolar concentrations. Optimum potency was exhibited by phosphodiester duplexes approximately 10 base pairs in length, and base composition was important only in the context of duplex stability. Phosphorothioate analogues were less potent. Although the molecular mechanism of action of these unique compounds is not yet known, they offer potential applications in cancer therapy and in studies of cell death. In addition, the path toward elucidation of the structure-based biological activity of these oligonucleotides should be especially instructive for researchers studying sequence-specific effects.

Animals↗
PubMed1994

Factors influencing the extent and regiospecificity of cross-link formation between single-stranded DNA and reactive complementary oligodeoxynucleotides.

Cross-link formation, within the duplex, by oligodeoxynucleotides containing a 5-[omega-(omega-haloacylamido)alkyl]-2'-deoxyuridine to a complementary oligodeoxynucleotide was investigated under conditions approximating the physiologic environment. The site and extent of crosslinking to the target strand were determined for several electrophilic haloacylamidoalkyl structures. The regiospecificity of alkylation was primarily determined by the length of the electrophilic haloacylamidoalkyl group, while the extent of reaction was dependent upon both the structure of the acylamidoalkyl group and the reactivity of the electrophile. Cross-linking was additionally modulated by the sequence of the duplex in the vicinity of the alkylation site. The exact placement of the electrophile adjacent to the targeted nucleophile, an N-7 group on a specific guanine base in the target strand, was the most important factor in determining the rate of reaction. With the optimal haloacylamidoalkyl structure and duplex sequence, the most rapid rate obtained was t1/2 = 1.3 h at 37 degrees C.

Base Sequence↗
PubMed1993

Facile preparation of nuclease resistant 3' modified oligodeoxynucleotides.

An efficient chemical procedure for the immobilization of carboxylate containing conjugate groups onto controlled pore glass (CPG) is described. The derivatized supports were used in the automated synthesis of an oligodeoxynucleotide (20-mer ODN) containing a 3' phosphodiester linked hexanol, aminohexyl, acridine, or cholesterol group. The stability of the oligomer in a hepatoma cell culture was found to be prolonged two to three fold by the presence of any of the 3' tails. By contrast, an aminohexyl group appended to the 5' terminus of the ODN only marginally improved its nuclease resistance. These data support the notion that antisense ODNs are primarily degraded by 3' exonucleases. Introduction of simple 3' tails which incorporate a normal phosphodiester linkage can increase ODN stability by interfering with these enzymes.

Base Sequence↗
PubMed1991

Preparation and hybridization properties of oligonucleotides containing 1-alpha-D-arabinofuranosylthymine.

A pentadecanucleotide was prepared from 1-alpha-arabinofuranosylthymine. This novel oligonucleotide was found to hybridize to oligodeoxyadenylate, although not a s strongly as pentadecathymidylate. It formed duplex hybrids with both DNA and RNA complements, and triplex structures with a duplex containing a (dT)15-(dA)15 tract within a more complex strand. The Tm of the duplex with polyadenylate was almost the same as that of (dT)15 and polyadenylate, while its Tm with (dA)15 was substantially lower than that of the natural counterpart. A selective benzoylation of the 2'-O of a 5'-blocked alpha-ara-thymine was developed to greatly simplify the preparation of suitable blocked material for use in preparation of oligonucleotides on the automated DNA synthesizer.

Arabinonucleosides↗
PubMed1988

Synthesis, intramolecular hydrogen bonding, and biochemical studies of clitocine, a naturally occurring exocyclic amino nucleoside.

The total synthesis of clitocine [6-amino-5-nitro-4-(beta-D-ribofuranosylamino)pyrimidine] (1), a nucleoside recently isolated from the mushroom Clitocybe inversa, has been accomplished. Glycosylation of 4,6-diamino-5-nitropyrimidine (4) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose afforded the protected nucleoside 6-amino-5-nitro-4-[(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl) amino]pyrimidine (5) in good yield exclusively as the beta-anomer. Deprotection of 5 with NaOMe/MeOH gave 1 as an 11.5:1 mixture of the beta- and alpha-anomers, respectively. Recrystallization from MeOH, followed by chromatography, afforded 1 containing less than 1% of its alpha-anomer. X-ray crystal data revealed a planar aglycon moiety in clitocine with each oxygen atom of the nitro group intramolecularly hydrogen bonded to the hydrogen atoms of the two adjacent amino functions. Clitocine inhibited L1210 cells in vitro with an ID50 of 3 X 10(-8) M. Clitocine was also found to be a substrate and inhibitor of adenosine kinase with a Ki value of 3 X 10(-6) M.

Adenosine Kinase↗
PubMed1988

Nucleosides of 1,4-thiazin-3-one and derivatives as tetrahedral intermediate analogues of enzymes in pyrimidine nucleoside metabolism.

Reaction of the trimethylsilylated derivative of 1,4-thiazin-3-one with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose in the presence of SnCl4 gave, after deblocking, 4-beta-ribofuranosyl-1,4-thiazin-3-one (8). Treatment of 1,4-thiazin-3-one with 1-chloro-2-deoxy-3,5-di-O-p-toluoyl-alpha-D-erythro-pentofuranose in the presence of sodium hydride provided, after deblocking, the corresponding 2-deoxy-beta-D-ribofuranosyl derivatives (19). Oxidation of 4-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)-1,4-thiazin-3-one (7) with 1 equiv of m-chloroperbenzoic acid resulted in 4-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)-1,4-thiazine-2,3-dione (9) and 4-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)-1,4-thiazin-3-one 1-oxide (10). Evidence is presented that indicates that the oxidation of the thiazine at the 2-position is due to a Pummerere rearrangement. The new compounds failed to show significant activity against tumor cell lines in culture, L1210 cells in vivo, virus cytotoxicity in cell culture, or cytidine deaminase.

Animals↗
PubMed1984

Design and synthesis of tetrahedral intermediate analogues as potential dihydroorotase inhibitors.

Three new heterocyclic analogues (4-6) of dihydroorotic acid were designed, synthesized, and tested as inhibitors of dihydroorotase. Each compound possessed a tetrahedral sulfur atom at the position equivalent to carbon 4 in the dihydroorotate ring in an attempt to mimic the presumed tetrahedral transition state in the course of the enzymatic reaction. Additionally, N-carbamyl-3-phosphonoalanine was prepared and evaluated as a dihydroorotase inhibitor. Compounds 4 and 6 were modest inhibitors (I50's of 0.52 and 0.18 mM, respectively), but the other candidate inhibitors showed little inhibition at 1 mM.

Amidohydrolases↗
PubMed1984

Inhibitors of inosinic acid dehydrogenase. 2-Substituted inosinic acids.

A series of 2-substituted inosine monophosphate (IMP) and inosine derivatives were synthesized and tested for inhibitory activity against IMP dehydrogenase from Escherichia coli. All of the IMP analogues that possessed electron-withdrawing substituents on the phenyl ring of a benzylthio group placed at the 2-position of IMP showed strong inhibition, which was competitive with IMP. No evidence of hydrophobic interactions of the 2-substituent with the enzyme was observed.

Escherichia coli↗
PubMed1984

2,5-Anhydro-1-deoxy-1-phosphono-D-altritol, an isosteric analogue of alpha-D-ribofuranose 1-phosphate.

Condensation of tetramethyl methylenebisphosphonate with 2,3-O-isopropylidene-5-O-trityl-D-ribose gave a mixture of 2,5-anhydro-1-deoxy-1-(diethoxyphosphinyl)-2,3 -O-isopropylidene-5-O-trityl-D-altritol and -allitol. Separation of the isomers and deprotection gave 2,5-anhydro-1-deoxy-1-phosphono-D-altritol and -allitol. The former is the stable isosteric methylenephosphonate analogue of alpha-D-ribose 1-phosphate, the ribose donor in nucleoside phosphorylase catalyzed nucleoside biosynthetic reactions. It did not, however, inhibit purine nucleoside phosphorylase at concentrations of 6 mM.

Animals↗
PubMed1981

Inhibition of inosinic acid dehydrogenase by 8-substituted purine nucleotides.

A series of 8-substituted derivatives of adenosine monophosphate (AMP) and inosine monophosphate (IMP) were synthesized and examined for their ability to inhibit Escherichia coli IMP dehydrogenase. All compounds studied were competitive inhibitors in IMP-dependent competition studies and lacked substrate activity. In oxidized nicotinamide adenine dinucleotide dependent studies, 8-(p-NO2PhCH2S)-IMP was noncompetitive and 8-(p-NO2PhCH2S)-AMP showed mixed inhibition. Multiple regression analysis showed that for the series of 8-(para-substituted-benzylthio)-AMPs and -IMPs, the electron-withdrawing ability of the para substituent on the benzylthio moiety correlated best with log Ki of the analogues.

Adenosine Monophosphate↗
PubMed1980

Synthesis and enzymatic and inotropic activity of some new 8-substituted and 6,8-disubstituted derivatives of adenosine cyclic 3',5'-monophosphate.

The synthesis of certain new 8-(arythio)- and 8-(alkylthio)-cAMP derivatives and N6-alkyl- and N6-dialkyl-8-(arylthio) and -8-(alkylthio) derivatives of cAMP is reported. On the basis of activation of protein kinase, several N6-alkyl-8-(benzylthio)-cAMP derivatives were selected for evaluation as inotropic agents using cat papillary muscle in vitro. Activity in these studies resulted in the selection of several analogues for in vivo studies in the anesthetized dogs. The best inotropic agent selected on the basis of in vivo studies was N6-butyl-8-(benzylthio)-cAMP (26), which exhibited an increase in blood-flow rate of 85% with no increase in heart rate. A large-scale synthesis of 26 from cAMP is reported via N1-alkylation, followed by a Dimroth rearrangement, reduction, bromination, and nucleophilic displacement via benzyl mercaptan. The N6-alkyl-8-substituted-cAMP derivatives represent a new class of potent inotropic agents. The direct mechanism of action of 26 suggests the possible utility of this cyclic nucleotide to treat clinical myocardial infarction by rapid intravenous infusion.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1979

2'-O-Acyl-6-thioinosine cyclic 3',5'-phosphates as prodrugs of thioinosinic acid.

A series of 2'-O-acyl derivatives of 6-thioinosine cyclic 3',5'-phosphate (6-HS-cRMP) were prepared and examined for their cytotoxic effects on S49 mouse lymphoma cells which were deficient in hypoxanthine-guanine phosphoribosyltransferase (HGPRTase). Cytotoxicity increased with the lipophilicity of the acyl group to a lowest EC50 of 65 micrometer for the 2'-O-palmityl derivative. Addition of a mutation in the gene for cAMP-dependent protein kinase to the HGPRTase-deficient cell line confers resistance to 2'-O-butyryl-cAMP but not to 2'-O-butyryl-6-HS-cRMP, indicating that the latter does not exert its toxic effect via activation of protein kinase. The time course of cell kill by 2'-O-palmityl-6-HS-cRMP resembled that of 6-mercaptopurine and not that of cyclic AMP in these cells. The data suggest that the intact cyclic nucleotides are penetrating the cells and being converted, by phosphodiesterase action and deacylation, to the first toxic metabolite of 6-mercaptopurine, thioinosinic acid.

Animals↗