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P F Torrence

Publications and source records attributed to P F Torrence.

At least 55 records · Page 3Linked to original sources
PubMed1992

Synthesis and biological activity of uronic acid analogues of 2-5A[5'-O-triphosphoryladenylyl(2----5')adenylyl-(2'----5')adenosine].

The oligonucleotide ppp5'A2'p5'A2'p5'A, known as 2-5A, is a potent translational inhibitor involved in some aspects of interferon action. To explore the specific function of the charged 5'-triphosphate moiety, we prepared a series of congeners in which the 5' region was hypermodified. Thus, uronic acid derivatives were substituted for the 5' terminal adenosine residue of 2-5A. Compounds 9, 10, 11 and 12 carried adenosine 5'-uronic acid, ethyl adenosine 5'-uronate, adenosine 5'-uronamide, and adenosine 5'-(N-ethyl)uronamide, respectively, in place of the 5' terminal adenosine triphosphate moiety of 2-5A. While all the analogues showed some weak interaction with the 2-5A-dependent endonuclease (RNase L), compound 9 showed the strongest binding ability, and while unable to activate the mouse RNase L, could activate human RNase at a concentration 100-fold greater than that required for the parent 2-5A. This result suggests that the function of the 5'(poly)phosphate moiety of 2-5A may be fulfilled by some other anionic moiety.

Adenine Nucleotides↗
PubMed1991

8-Methyladenosine-substituted analogues of 2-5A: synthesis and their biological activities.

8-Methyladenosine-substituted analogues of 2-5A, p5'A2'p5'A2'p5'(me8A), p5'A2'p5'(me8A)2'p5'(me8A), p5'(me8A)2'p5'(me8A)2'p5'(me8A), and p5'(me8A) 2'p5'A2'p5'A, were prepared via a modification of a lead ion-catalyzed ligation reaction. These 2-5A monophosphates were converted into the corresponding 5'-triphosphates. Substitution of an 8-methyladenosine residue at the third position (2'-terminus) of the oligonucleotides increased the stability to snake venom phosphodiesterase digestion. Both binding and activation of mouse liver 2-5A dependent ribonuclease (RNase L) by the various 8-methyladenosine-substituted 2-5A analogues were examined. Among the 8-methyladenosine-substituted trimer analogues, the analogues with 8-methyladenosine residing in the 2'-terminal position showed the strongest binding affinity and were several times more effective than 2-5A itself as an inhibitor of translation.

Adenine Nucleotides↗
PubMed1991

Solid-state and solution conformation of 3'-amino-3'-deoxythymidine, precursor to a noncompetitive inhibitor of HIV-1 reverse transcriptase.

The recent finding that 3'-amino-3'-deoxythymidine 5'-triphosphate is a noncompetitive inhibitor of the HIV-1 reverse transcriptase (Kedar, P.S.; et al. Biochemistry 1990, 29, 3603-3611), prompted an investigation of the conformation of 3'-amino-3'-deoxythymidine. An X-ray diffraction study has revealed that the glycosidic torsion angle of the nucleoside is in the less common syn region and this solid-state geometry is stabilized by a three-dimensional network of self-associated hydrogen-bonded molecules. On the other hand, the aqueous solution conformation, as determined by 1H NMR, places the glycosidic torsion angle in the more usual anti region with the sugar in an equilibrium between C3'-endo and C2'-endo puckering. The energy barrier between the solid-state and solution conformation is relatively low as was demonstrated by the MM2 calculations.

Chemical Phenomena↗
PubMed1991

2',5'-oligoadenylates inhibit relaxation of supercoiled DNA by calf thymus DNA topoisomerase I.

DNA topoisomerases interconvert various topological isomers of DNA and play key roles in replication and gene expression. The possible involvement of the 2',5'-oligoadenylates (2-5A) system in cell growth, regulation, and cell differentiation led us to investigate the effects of 2-5A on mammalian topoisomerases. We found that the calf thymus type I topoisomerase was inhibited by a variety of 2-5A compounds. The level of inhibition was dependent upon the number of residues and the degree of phosphorylation at the 5' terminus. The 5'-triphosphorylated 2',5' hexamer, ppp(Ap)5A, was the most effective, strongly reducing relaxation at less than micromolar concentrations. These results raise the possibility that physiological concentrations of 2-5A of sufficient chain length may be capable of regulating gene expression by virtue of a direct inhibition of DNA topoisomerase I.

Adenine Nucleotides↗
PubMed1990

Photochemical crosslinking in oligonucleotide-protein complexes between a bromine-substituted 2-5A analog and 2-5A-dependent RNase by ultraviolet lamp or laser.

2',5'-oligoadenylates known as 2-5A [px(A2'p)nA; chi = 2 or 3, n greater than or equal to 2] are produced in interferon-treated cells in response to double-stranded RNA. 2-5A binds with high affinity to a 2-5A-dependent RNase resulting in the cleavage of single-stranded RNA. An efficient, rapid, and extremely sensitive photoaffinity labeling method was developed to facilitate detection of 2-5A-dependent RNase. A bromine-substituted and radioactive derivative of 2-5A, the 5'-monophosphate, p(A2'p)2(br8A2'p)2A3'-[32P]Cp, was synthesized as probe for 2-5A-dependent RNase. Even though this bromine-substituted analog of 2-5A bore no 5'-terminal triphosphate or diphosphate, it bound to 2-5A-dependent RNase with the same high affinity as did 2-5A per se but it was a less effective activator of the RNase under the present assay conditions. The presence of bromine atoms in the 2-5A analog enhanced by more than 200-fold crosslinking to 2-5A-dependent RNase under a uv lamp; many additional polypeptides were also labeled but at much lower levels. Furthermore, using high-intensity uv laser irradiation (308 nm) covalent attachment of the bromine-substituted 2-5A analog to 2-5A-dependent RNase was readily achieved within 10(-6) s.

Adenine Nucleotides↗
PubMed1990

Inhibition of the RNA polymerase of vesicular stomatitis virus by ppp5'A2'p5'A and related compounds.

The diadenylate triphosphates ppp5'A2'p5'A and ppp5'A3'p5'A were found to inhibit the purified RNA polymerase ('nucleocapsid') complex from vesicular stomatitis virus (VSV). The corresponding diadenylate monophosphate p5'A2'p5'A did not inhibit, nor did the triadenylate triphosphate ppp5'A2'p5'A2'p5'A; the diadenylate diphosphate pp5'A2'p5'A had intermediate inhibitory activity. Increasing the concentration of ATP, GTP or CTP in the reaction mixture decreased inhibition by ppp5'A2'p5'A, while UTP had minimal or no protective effect. ppp5'A2'p5'A did not protect the RNA polymerase from inactivation by N-ethylmaleimide. This suggests that the action of ppp5'A2'p5'A occurs at a site on the enzyme that is distinct from the N-ethylmaleimide-protecting, ATP-binding site characterized previously.

Adenine Nucleotides↗
PubMed1989

Conformational analysis of brominated pA2'-5'A2'-5'A analogs. An NMR and model-building study.

NMR and model-building studies were carried out on pA2'-5'A2'-5'A and analogs in which one or more of the A residues were replaced by 8-bromoadenosine. Chemical shifts, coupling constants and NOE data were used to obtain structural information. The N/S equilibrium constant of the ribose rings as well as the phase angles and puckering amplitudes were determined from the experimental coupling constants with the aid of an improved version of the PSEUROT program. Chemical shifts in combination with NOE data were used to monitor base-base interactions and the orientation of the bases (syn or anti). The combined data suggest that different types of stacking interactions are present in the various compounds. Bromination of the first or second residue in the trimers results in a preference for N-type sugar and syn orientation of the base in these residues. When A(3) is brominated, an S-type sugar conformation together with a syn orientation of the base is favoured at the 2' terminus. Energy-minimized models of the different stacking interactions are presented which fit the present collection of data. The possible correlation between biological activity of these compounds and their conformation is briefly discussed.

Adenosine↗
PubMed1989

8-Methyladenosine-substituted analogs of 2-5A: synthesis and properties.

Four 8-methyladenosine-substituted analogs of 2-5A were obtained by a synthesis which involved a modification of the lead ion-catalyzed ligation reaction. Substituent of an 8-methyladenosine residue at the third position (2'-terminal) of the oligonucleotides increased the stability to snake venom phosphodiesterase digestion.

Adenine Nucleotides↗
PubMed1988

AIDS dementia: synthesis and properties of a derivative of 3'-azido-3'-deoxythymidine (AZT) that may become 'locked' in the central nervous system.

In an attempt to provide a derivative of 3'-azido-3'-deoxythymidine (AZT) which might be sequestered in the central nervous system and release AZT, the dihydropyridine ester 5'-(1,4-dihydro-1-methyl-3-pyridinylcarbonyl)-3'-deoxythymidine, was synthesized in a three step sequence. This material showed potent anti-HIV-1 activity in MT-4 cells most probably by hydrolysis to the parent nucleoside, AZT. This dihydropyridine derivative of AZT could be easily oxidized to a positively charged pyridinium derivative of AZT in rat brain cytosol. In turn the pyridinium form could be hydrolyzed, non-enzymatically, to AZT.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Only one 3'-hydroxyl group of ppp5' A2'p5'A2'p5' A (2-5A) is required for activation of the 2-5A-dependent endonuclease.

To investigate the relative importance of each of the ribose 3'-hydroxyl groups of 2-5A (ppp5' A2'p5'A2'-p5' A) in determining binding to and activation of the 2-5A-dependent endonuclease (RNase L), the 3'-hydroxyl functionality of each adenosine moiety of 2-5A trimer triphosphate was sequentially replaced by hydrogen. The analog in which the 5'-terminal adenosine was replaced by 3'-deoxyadenosine (viz. ppp5'(3'dA)-2'p5' A2'p5' A) was bound to RNase L as well as 2-5A itself and was only 3 times less potent than 2-5A as an activator of RNase L. On the other hand, when the second adenosine unit was replaced by 3'-deoxyadenosine (viz. ppp5' A2'p5'(3'dA)2'p5' A), binding to RNase L was decreased by a factor of eight relative to 2-5A trimer and, even more dramatically, there was a 500-1000-fold drop in ability to activate the 2-5A-dependent endonuclease. Finally, when the 3'-hydroxyl substituent was converted to hydrogen in the 2'-terminal residue of 2-5A, a significant increase in both binding and activation ability occurred. We conclude that only the 3'-hydroxyl group of the second (from the terminus) nucleotide residue of 2-5A is needed for effective activation of RNase L.

Adenine Nucleotides↗
PubMed1987

Degradation by the 2',5'-phosphodiesterase activity of mouse cells requires the presence of a ribo hydroxyl group in the penultimate position of the oligonucleotide substrate.

A series of 9-beta-D-xylofuranosyladenine (xyloA or xyloadenosine) substituted analogs of 2-5A core trimer and tetramer were examined for their ability to be degraded by the 2',5'-phosphodiesterase activity of cytoplasmic extracts of mouse L cells. Two distinct groups of xyloA-substituted analogs could be readily discriminated. The first group contained xyloadenosine at the 2'-termini and included A2'p5'A2'p5'(xyloA) and A2'p5'A2'p5'A2'p5'(xyloA). These oligomers behaved as did their parent oligoadenylates in that they were equally sensitive to degradation by the 2',5'-phosphodiesterase activity. The second group of oligonucleotides bore a xyloadenosine residue in the penultimate nucleotide residues of the oligomers and included A2'p5'(xyloA)2'p5'(xyloA), (xyloA)2'p5'(xyloA)2'p5'(xyloA), A2'p5'A2'p5'(xyloA)2'p5'(xyloA) and (xyloA)2'p5' (xyloA)2'p5'(xyloA)2'p5'(xyloA). This group was quite resistant to 2',5'-phosphodiesterase activity. In all, the findings demonstrate that the ribo configuration 3'-hydroxyl group in the penultimate nucleotide of the oligonucleotide substrate is a prerequisite for the 2',5'-phosphodiesterase activity.

Adenine Nucleotides↗
PubMed1987

Purine 8-bromination modulates the ribonuclease L binding and activation abilities of 2',5'-oligoadenylates. Possible influence of glycosyl torsion angle.

Analogs of the 2',5'-linked adenylate trimer diphosphate (pp5'A2'p5'A2'p5'A or 2-5A) containing 8-bromoadenosine in the first, second, third, first and third, or second and third nucleotide positions (from the 5' terminus) were synthesized and found to vary dramatically in their ability to bind to and activate the RNase L of mouse L cells. Whenever the 8-bromoadenosine residue was substituted for adenosine in the first or 5'-terminal residue, there resulted a marked decrease in ability to bind to the 2-5A-dependent endonuclease. A similar result was obtained when the second adenosine nucleotide was replaced by 8-bromoadenosine. To the contrary, all analogs that bore an 8-bromoadenosine (br8A) in the third or 2'-terminal position were bound about as well as parent 2-5A to RNase L. Additionally, the 5'-diphosphate pp5'A2'p5'A2'p5' (br8A) was 10 times more effective than 2-5A as an inhibitor of translation. An increase in stability could not explain this significantly enhanced ability since the 2'-terminally brominated analog showed a similar half-life to 2-5A itself. Finally of particular interest was the analog monophosphate p5'A2'p5'(br8A)2'p5'(br8A) which possessed nearly 10% of the translational inhibitory activity of 2-5A triphosphate itself. These results suggest that changes in the base-sugar torsion angles of 2-5A may modulate both binding to and activation of mouse L cell RNase L.

Adenine Nucleotides↗
PubMed1987

Respective role of each of the purine N7 nitrogens of 5'-O-triphosphoadenylyl(2'----5')adenylyl(2'----5')adenosine in binding to and activation of the RNase L of mouse cells.

Through a combination of chemical and enzymatic approaches a series of sequence-specific tubercidin-substituted ppp5'A2'p(5'A2'p)n5'A (n = 1 to about 10; 2-5A) analogues were generated. In addition to the previously developed methodology of Imai and Torrence [Imai, J., & Torrence, P.F. (1985) J. Org. Chem. 50, 1418-1420], a new approach to synthesis of 2',5'-linked oligonucleotides utilized adenosine in 3',5' linkage as a precursor to the targeted 5'-terminus of the desired product. For instance, A3'p5'A could be condensed under conditions of lead ion catalysis with tubercidin 5'-phosphate to give A3'p5'A2'p5'(c7A). Treatment with the 3',5'-specific nuclease P1 led to p5'A2'p5'(c7A). The combined use of the above procedures led to the synthesis of p5'(c7A)2'p5'A2'p5'A, p5'A2'p5'(c7A)2'p5'A, p5'A2'p5'A2'p5'(c7A), and p5'A2p5'(c7A)2'p5'(c7A), which were converted to their corresponding 5'-triphosphates by the usual methods. Evaluation of these analogues for their ability to bind to and activate the 2-5A-dependent endonuclease (RNase L) of mouse L cells showed that there were small changes (less than or equal to 10-fold) in the ability of the four tubercidin analogues to bind to RNase L. However, whenever the first and/or third adenosine nucleotide units were replaced by tubercidin, a dramatic decrease in ability to activate RNase L occurred. Only the second (from the 5'-terminus) adenosine residue could be replaced by tubercidin without any effect on RNase L activation ability.

Adenine Nucleotides↗
PubMed1986

2',5'-Phosphodiesterase activity depends upon the presence of a 3'-hydroxyl moiety in the penultimate position of the oligonucleotide substrate.

3'-Deoxyadenosine (3'dA, cordycepin)-substituted analogs of 2-5A core 5'-monophosphate (p5'A2'p5'A2'p5'A) were examined for their sensitivity toward degradation by the 2'-phosphodiesterase activity in cytoplasmic extracts of mouse L cells. The analogs, p5'(3'dA)-2'p5'A2'p5'A, p5'(3'dA)2'p5'A2'p5'(3'dA) and p5'A2'p5'A2'p5'(3'dA) were degraded at a rate comparable to p5'A2'p5'A2'p5'A itself. On the other hand, under the assay conditions examined p5'A2'p5'(3'dA)2'p5'A, like p5'(3'dA)2'p5'(3'dA)2'p5'(3'dA), was completely resistant to degradation. The data imply that sensitivity to the 2',5'-phosphodiesterase activity of mouse L cells requires the presence of 3'-hydroxyl moiety in the penultimate nucleotide.

Adenine Nucleotides↗
PubMed1986

Activation of 2-5A-dependent RNase by analogs of 2-5A (5'-O-triphosphoryladenylyl(2'----5')adenylyl(2'----5')adenosine ) using 2',5'-tetraadenylate (core)-cellulose.

A variety of 2-5A (px(A2'p)nA; x = 2 or 3, n greater than or equal to 2) analogs were assayed for their abilities to activate murine 2-5A-dependent RNase (subsequently "the nuclease") using a recently developed method. This technique consists of immobilizing and partially purifying the nuclease using core-cellulose [A2'p)3A-cellulose) and then monitoring the breakdown of poly(U)-3'-[32P]Cp into acid-soluble fragments. Several 5'-adenosinecapped analogs of 2-5A (containing a tetra-, tri-, or diphosphate) were analyzed, and it was found that reducing the number of phosphoryl groups between the 5' to 5'-diadenosine linkages resulted in a progressive loss of activity. Because A5' pppp(A2'p)3A was a potent activator of the nuclease yet stable during the assay these results suggested that a free 5'-phosphoryl group may not be required for the activation of the nuclease. A number of 8-bromoadenosine-substituted analogs of 2-5A were also studied. Curiously, the brominations decreased the activities of the 5'-di- and triphosphorylated molecules while substantially increasing the activities of the 5'-monophosphorylated species. The results indicated that a tri- or diphosphate moiety on the 5'-end of 2-5A or the presence of ATP is not absolutely required for the nuclease to be active. Furthermore, the ATP analog, beta, gamma-methylene ATP, did not inhibit the activity of the nuclease. Finally, a 3',5'-phosphodiester linkage isomer of 2-5A and a 3'-deoxy (cordycepin) analog of 2-5A were tested, and both were found to be completely without activity.

Adenine Nucleotides↗