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Biomedical subjects

R T Walker

Publications and source records attributed to R T Walker.

At least 127 records · Page 7Linked to original sources
PubMed1979

(E)-5-(2-Bromovinyl)-2'-deoxyuridine: a potent and selective anti-herpes agent.

Of a series of five newly synthesized 2'-deoxyuridine derivatives, including 5-vinyl-dUrd, 5-ethynyl-dUrd, 5-(1-chlorovinyl)-dUrd, (E)-5-(2-bromovinyl)-dUrd, and (E)-5-(2-iodovinyl)-dUrd, the last two compounds were found to exert a marked inhibitory effect on the replication of herpes simplex virus type 1 [ID50 (mean inhibitory dose), 0.004-0.02 microgram/ml]. Both (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd were highly selective in their anti-herpes activity in that they did not affect the growth or metabolism of the host (primary rabbit kidney) cells unless drug concentrations were used that were 5,000- to 10,000-fold greater than those required to inhibit virus multiplication. In this sense (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd proved more selective in their activity against herpes simplex virus type 1 than all other anti-herpes compounds that have been described so far. In animal model systems (namely, cutaneous herpes infections of athymic nude mice), (E)-5-(2-bromovinyl)-dUrd suppressed the development of herpetic skin lesions and mortality therewith associated, whether the compound was administered topically or systemically. Under the same conditions, the standard anti-herpes drug 5-iodo-dUrd (Idoxuridine) offered little, if any, protection. Although the precise mechanism of action of (E)-5-(2-bromovinyl)-dUrd and (E)-5-(2-iodovinyl)-dUrd remains to be established, preliminary findings indicate that they do not specifically act at the thymidylate synthetase step.

Animals↗
PubMed1979

Pharmacokinetics of E-5-(2-bromovinyl)-2'-deoxyuridine in mice.

The pharmacokinetics of the newly developed anti-herpes agent, E-5-(2-bromovinyl)-2'-deoxyuridine, was compared with that of the standard anti-herpes drug 5-iodo-2'-deoxyuridine. Both compounds were administered to mice at 100 mg/kg by either the intraperitoneal, subcutaneous, or oral route. The active blood drug levels achieved by E-5-(2-bromovinyl)-2'-deoxyuridine were considerably higher than those attained by 5-iodo-2'-deoxyuridine (serum peak concentrations: 40 to 100 and 4 to 10 mug/ml, respectively). Active blood drug levels could still be found 320 min after oral administration of E-5-(2-bromovinyl)-2'-deoxyuridine.

Animals↗
PubMed1979

Relative potencies of different anti-herpes agents in the topical treatment of cutaneous herpes simplex virus infection of athymic nude mice.

Thirteen established anti-herpes compounds have been directly compared in a single assay system for their effects on the development of herpetic skin lesions, and mortality associated therewith, in athymic nude (nu/nu) mice inoculated intracutaneously with herpes simplex virus type 1 (KOS). When applied topically (at 1% in a water-soluble ointment), phosphonoacetic acid, E-5-(2-bromovinyl)-2'-deoxyuridine, acycloguanosine, and trisodium phosphonoformate emerged as the most active agents.

Animals↗
PubMed1978

The nucleotide sequence of formylmethionine tRNA from Mycoplasma mycoides sp. capri.

The nucleotide sequence of Mycoplasma mycoides sp. capri PG3 formylmethionine tRNA has been determined, using in vitro labeling techniques, to be pC-G-C-G-G-G-G-s4U-A-G-A-G-C-A-G-U-D (U)-G-G-D-A-G-C-U-C-G-C-C-G-G-G-C-U-C-A-U-A-A-C-C-C-G-G-A-G-G-C-C-G-C-A-G-G-U-psi- C-G-A-G-U-C-C-U-G-C-C-C-C-C-G-C-A-A-C-C-AOH. This tRNA contains only three modified nucleosides s4U, D and psi, all of which are derived from uridine. Both in the structural features which distinguish eukaryotic from prokaryotic initiator RNAs and in the overall sequence, this tRNA resembles a typical prokaryotic initiator tRNA. A comparison of the sequence of this tRNA with those of other prokaryotic initiator tRNAs suggests that taxonomically the Mycoplasma may be less related to the Cyanophyta (Anacystis nidulans) than to the bacteria and less related to the Enterobacteriaceae (Escherichia coli) than to the Bacillaceae (Bacillus subtilis).

Base Sequence↗
PubMed1976

Incorporation of 5-substituted uracil derivatives into nucleic acids. Part IV. The synthesis of 5-ethynyluracil.

5-Acetyluracil (I) has been treated with POCI3 to give 5-(1-chlorovinyl)-2,4-dichloropyrimidine (II). Treatment of II with KOEt gave a mixture of 2-ethoxy-5-ethynyl-4 (3H)-pyrimidinone (IIIA) and 4-ethoxy-5-ethynyl-2 (1H)-pyrimidinone (IIIB). IIIA and IIIB were isolated and characterised. The mixture of IIIA and IIIB upon treatment with HCI gave 5(1-chlorovinyl)uracil (IV). Reaction of IV with KOEt gave 5-ethynyluracil (V). 5-Ethynyluracil was more easily obtained by the treatment of II with KOH in aqueous dioxan.

Alkynes↗
PubMed1975

Formylatable methionine transfer RNA from Mycoplasma: purification and comparison of partial nucleotide sequences with those of other prokaryotic initiator tRNAs.

The major species of the formylatable methionine tRNA from Mycoplasma mycoides var capri has been purified. The 5'- and 3'-terminal sequences of the purified tRNA are pC-G- and C-A-A-C-C-AOH, respectively. Thus, this tRNA also contains the unique structural feature found in two other prokaryotic initiator tRNAs in that the first nucleotide at the 5'-end cannot form a Watson-Crick type of base-pair to the fifth nucleotide from the 3'-end. The Mycoplasma tRNA does not contain ribothymidine; however, a specific uridine residue in the sequence G-U-psi-C-G- can be enzymatically methylated by E. coli extracts to yield G-T-psi-C-G. Since ribothymidine is absent in crude tRNA from this strain of Mycoplasma, the absence of T is probably due to the lack of a U yields T modifying enzyme.

Base Sequence↗
PubMed1975

The preparation of 5-cyanouracil and 5-cyano-2'-deoxyuridine from the corresponding 5-iodo derivative and cuprous cyanide.

5-Cyanouracil has been prepared in high yield from cuprous cyanide and 5-iodouracil. The deoxynucleoside has been similarly prepared form 5-iodo-2'-deoxyuridine and this has enabled these compounds to be labelled with (14-C) cyanide. Attempts have been made to incorporate 5-cyanouracil into Escherichia coli 15T and into Mycoplasma mycoides var. capri DNA under conditions in which several other 5-substituted uracils have been incorporated, but without success. Similarly 5-cyano-2'-deoxyuridine could not be incorporated into the DNA of T3 phage under conditions in which 5-bromo-2'-deoxyuridine is easily incorporated. These results suggest that the criteria for a 5-substituted uracil to be incorporated into DNA in vivo depends on some factor other than the size of the substituent.

Chemical Phenomena↗
PubMed1975

Synthetic analogues of polynucleotides. (Part) XIV. The synthesis of poly (3'-0-carboxymethyl-2'-deoxycytidine) and its interaction with polyinosinic acid.

Poly (3'-O-carboxymethyl-2'-deoxyctidine) (VII) has been synthesised by the polymerisation of 3'-O-carboxymethyl-4-N-phenoxyacety-2'-deoxycytidine (V) and removal of the phenoxyacetyl groups under acidic conditions. V was obtained by the action of 2,4-dinitrophenyl phenylacetate on 3'-O-carboxymethyl-5'-O-triphenylmethyl-2'-deoxycytidine (III) followed by removal of the triphenylmethyl group under carefully controlled acidic conditions. The polymer, VII gave a hypochromic effect of about 20% at 250nm when mixed with poly (1) in 0.2Macetate, pH 5.0. It appeared, therefore, that a complex was formed. Upon heating a solution of this complex there was an initial decrease in optical density followed by a much larger increase to give a Tm of about 60 degrees. Attempts to form the 3'-O-carboxymethyl derivative of 4-N-phenoxyacetyl-5'-O-'triphenylmethyl-2'-deoxycytidine to give a shorter synthetic route to VII were not successful. 3'-O-Carboxymethyl-2'-deoxycytidine was obtained by removal of thetriphenylmethyl group from III. Attempts to polymerise this compound in concentrated aqueous solution with a water-soluble carbodiimide were not successful.

Deoxycytidine↗