Biomedical subjects
Publications and source records attributed to R T Walker.
A practical 7-step synthesis of benzyl 3,5-di-O-benzyl-2-deoxy-1,4-dithio-D-erythro-pentofuranoside is described and the product has been used in the synthesis of some 4'-thio-2'-deoxynucleosides. These novel nucleoside analogues have potentially useful biological activity and are resistant to phosphorolysis.
In the search for novel derivatives of 1-[2-(hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT), we have found that several 5-ethyl-6-(3,5-dimethylphenylthio)uracil and 5-ethyl-6-(3,5-dimethylbenzyl)uracil analogues are exquisitely potent and selective inhibitors of human immunodeficiency virus type 1 (HIV-1) replication in a variety of cell culture systems. Of this series, 5-ethyl-1-ethoxymethyl-6-(3,5-dimethylbenzyl)uracil (E-EBU-dM) emerged as the most active congener. Its 50% inhibitory concentration for HIV-1 (HTLV-IIIB) in MT-4 cells and peripheral blood lymphocytes is 2.2 and 0.45 nM, respectively. These concentrations are more than 10(5)-fold lower than the 50% cytotoxic concentrations of E-EBU-dM for the host cells. All compounds proved equally inhibitory to a number of clinical HIV-1 isolates, including a 3'-azido-2',3'-dideoxythymidine-resistant variant. However, as previously noted for HEPT, they do not inhibit human immunodeficiency virus type 2 replication. Reverse transcriptase assays have revealed that these HEPT derivatives act specifically on HIV-1 reverse transcriptase, according to a mechanism that is different from that of the dideoxynucleosides.
A series of aryl bis(3'-O-acetylthymidin-5'-yl) phosphate derivatives have been synthesized in order to find a suitable aryl derivative which would hydrolyze to the bis(nucleosid-5'-yl) phosphate under physiological conditions. The 4-(methylsulfonyl)phenyl derivative was selected and 4-(methylsulfonyl)phenyl bis[(E)-5-(2-bromovinyl)-2'-deoxyuridin-5'-yl] phosphate (6d) and bis[2-(guanin-9-ylmethoxy)ethoxy]-4-(methylsulfonyl)phenyl phosphate (7b) were prepared. The former compound (6d) was stable in human serum and only following hydrolysis to the 5'-5'-linked diester (half-life of 17 h at pH 7.7) was it enzymatically degraded very rapidly by phosphodiesterases. Compounds 6d and 7b were evaluated for antiherpesvirus effects, both in vitro and in vivo. Their antiviral spectrum and potency was remarkably similar to that of (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) and 9-[(2-hydroxyethoxy)-methyl]guanine (ACV), suggesting that they only act as prodrugs of BVDU and ACV, respectively. However, compound 6d did show unexpected toxicity, which could be explained by the liberation of BVDUMP following penetration of the triester into the cell.
(E)-5-(2-Bromovinyl)-2'-deoxy-5'-O-(3-methyl-2-oxo-5-formyl-1,3,2- oxazaphosphacyclopentan-2-yl)uridine has been synthesized and, under physiological conditions and without the necessity for enzyme activity, has been shown to yield the 5'-nucleotide in vitro. Unfortunately this compound is not sufficiently stable in solution for it to be tested in vivo. The biological properties of this and some related derivatives of (E)-5-(2-bromovinyl)-2'-deoxyuridine and acyclovir have been evaluated in in vitro and in vivo systems designed to show the effects of any intracellular liberation of the nucleotide. Although some of the derivatives are probably acting as prodrugs of the active nucleosides, there is no evidence for the liberation of meaningful concentrations of the 5'-nucleotide by any of the compounds.
The synthesis and antiviral activity of a number of 3'-C-difluoromethyl and 3'-deoxy-3'-C-fluoromethyl nucleosides are reported. The 3'-C-difluoromethyl nucleosides 26a and 26b were obtained by treatment of the corresponding 2',5'-di-O-protected-3'-C-formyl nucleosides 25a and 25b with (diethylamino)sulfur trifluoride (DAST). Removal of the 2'-O-protecting group from 26a and subsequent reaction with DAST furnished the 2'-deoxy-2'-fluoro-beta-D-ribo-pentofuranosyl nucleoside 29. Selective fluorination with DAST of the 5'-O-protected analogues 3'-deoxy-3'-C-hydroxymethyl derivatives 13a and 13b gave the 3'-deoxy-3'-C-fluoromethyl derivatives 30a and 30b, while nonselective fluorination afforded the 2',3'-dideoxy-2'-fluoro-3'-C-fluoromethyl analogues 31a and 31b. The deprotected uracil analogue 17a was iodinated to the 5-iodouracil derivative 18. The fully deprotected fluorinated 3'-C-branched nucleosides 14-18 and 32 were evaluated for their antiviral activity. None were active against human immunodeficiency virus type-1 (HIV-1) at concentrations up to 100 microM. However, 5-iodouracil analogue 18 showed activity, comparable to that of acyclovir, against varicella zoster virus without observed cytotoxicity.
A series of 3'-branched-chain sugar nucleosides, in particular 3'-deoxy-3'-C-hydroxmethyl nucleosides, have been synthesized and evaluated as antiviral agents. Reaction of 1-(2,3-epoxy-5-O-trityl-beta-D-lyxo-pentofuranosyl) derivatives 12 and 13, of uracil and thymine, respectively, with 5,6-dihydro-2-lithio-5-methyl-1,3,5-dithiazine 14 afforded the corresponding 3'-functionalized nucleosides 15 and 16, respectively. Replacement of the trityl group with tertbutyldiphenylsilyl allowed high yielding hydrolysis of the 3'-function to give the 3'-deoxy-3'-C-formyl-beta-D-arabino-pentofuranosyl nucleosides 21 and 22. Desilylation afforded the 1-(3-deoxy-3-C-formyl-beta- D-lyxo-pentofuranosyl) 3',5'-O-hemiacetal nucleosides 33 and 34, respectively. Reduction of the formyl group of 21 and 22, followed by desilylation, yielded the 3'-deoxy-3'-C-(hydroxymethyl)-beta-D-arabino- pentofuranosyl) analogues 7 and 8, respectively. The uracil base moiety of 7 was converted to 5-iodouracil and then to (E)-5-(2-bromovinyl)uracil to furnish an analogue 10 of BVaraU. The 1-(3-deoxy-3-C-(hydroxymethyl)-beta-D-lyxo-pentofuranosyl) and 1-(2,3-dideoxy-3-C-(hydroxymethyl)-beta-D-erythro-pentofuranosyl) derivatives of uracil (31 and 6, respectively) and 5-iodouracil (32 and 9, respectively) were also obtained. All novel, fully deprotected nucleoside analogues were evaluated for antiviral activity against human immunodeficiency virus type-1, herpes simplex virus types-1 and -2, varicella zoster virus, human cytomegalovirus and influenza A. Of the compounds tested only (E)-5-(2-bromovinyl)-1-[3-deoxy- 3-C-(hydroxymethyl)-beta-D-arabino-pentofuranosyl]uracil (10) inhibited VZV (alone), but did so at concentrations well below the cytotoxicity threshold.
Explore the source record for details and available documents.
To improve the anti-HIV activity of 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT), a variety of its analogues were synthesized. Introduction of SR group to the C-6 position was carried out based on LDA lithiation followed by the reaction of aryl- or alkyl disulfide. An addition-elimination reaction of a 6-phenylsulfinyl derivative was used for synthesizing the analogues having OR or NHR group at the C-6 position. The C-5 modified derivatives were synthesized mainly based on LTMP lithiation of a 6-phenylthio derivative. Modification at the 2- or 4-position was also carried out. Some compounds prepared in the present study showed higher activity than HEPT.
A novel 6-substituted acyclouridine derivative, 1-[(2-hydroxy-ethoxy) methyl]-6-phenylthiothymine (HEPT), has proved to be a potent and selective inhibitor of human immunodeficiency virus type 1 (HIV-1) in vitro. HEPT inhibits HIV-1 replication in various T4 cell cultures as well as peripheral blood lymphocytes and macrophages. The 50% antiviral effective concentration for HIV-1 (HTLV-IIIB) in MT-4 cells is 7.0 microM, while the 50% cytotoxic concentration for mock-infected MT-4 cells is 740 microM. Although HEPT is inhibitory to various strains of HIV-1, it has no effect on the replication of other retroviruses including HIV type 2. In contrast with the dideoxynucleoside (i.e. azidothymidine) 5'-triphosphates, the triphosphate of HEPT does not interact with HIV-1 reverse transcriptase. The mechanism of action of HEPT remains subject of further study.
Explore the source record for details and available documents.
Racial differences in dental crown morphology have long been recognized, but the frequency of genetically determined variations in root form and root canal anatomy has not been established. The features of root and root canal morphology occurring at particularly high frequency in Mongoloid populations are now being documented, and the implications that such features may have upon clinical endodontics are now being reported. This paper reviews the endodontic morphology studies which have been conducted in the past and emphasizes the way in which racial divergence has had a direct influence upon the root and root canal anatomy of teeth of the adult dentition.
Bacillus stearothermophilus large ribosomal subunits were reconstituted in the presence of 5S rRNAs from different origins and tested for their biological activities. The results obtained have shown that eubacterial and archaebacterial 5S rRNAs can easily substitute for B. stearothermophilus 5S rRNA in the reconstitution, while eukaryotic 5S rRNAs yield ribosomal subunits with reduced biological activities. From our results we propose an interaction between nucleotides 42-47 of 5S rRNA and nucleotides 2603-2608 of 23S rRNA during the assembly of the 50S ribosomal subunit. Other experiments with eukaryotic 5.8S rRNAs reveal, if at all, a very low incorporation of these RNA species into the reconstituted ribosomes.
Explore the source record for details and available documents.
Treatment of 3',5'-di-O-acetyl-(E)-5-(2-bromovinyl)-2'-deoxyuridine (2) with p-chlorophenyl phosphorodichloridate and 1,2,4-triazole gave 1-(3,5-di-O-acetyl-2-deoxy-beta-D-erythro-pentofuranosyl)-(E)-5-(2-br o movinyl)- 4-(1,2,4-triazol-1-yl)pyrimidin-2(1H)-one (3). Reaction of 3 with ammonia gave (E)-5-(2-bromovinyl)-2'-deoxycytidine (1), the overall yield from 2 being 60%. A similar 4-(1,2,4-triazol-1-yl) derivative (4) was obtained from 3',5'-di-O-acetyl-thymidine by the use of phosphoryl chloride as the condensing agent. Treatment of thymidine with trimethylsilyl chloride and then with phosphoryl chloride and 1,2,4-triazole gave upon workup 1-(2-deoxy-beta-D-erythro-pentofuranosyl)-5-methyl-4(1,2,4-triazol -1-yl) pyrimidin-2(1H)-one (5). (E)-5-(2-Bromovinyl)-2'-deoxyuridine (BVDU) when similarly treated gave the corresponding (E)-5-(2-bromovinyl) compound 7. A minor product formed in both cases was a 4-(1,2,4-triazol-1-yl) derivative in which the nucleoside 5'-hydroxyl group had been replaced by chlorine (6 and 8). Whereas compounds 4-6 and 8 did not exhibit a selective antiviral effect, compounds 1-3 and 7 proved almost as active as the reference compound BVDU. In particular, compound 7, the 4-triazolyl derivative of BVDU, would seem worth pursuing for its potential as an inhibitor of herpes simplex virus type 1 and varicella-zoster virus.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.