Addition of 2,3-Dihydrofuran to N2-Acetyl-8-bromoguanine

Abstract

N₂-Acetyl-8-bromoguanine has been found to react readily with 2,3-dihydrofuran in DMF in the presence of acid catalyst at room temperature to give 9-(tetrahydrofuryl-2)-8-bromo-N₂-acetylguanine in high yield. The structures of this compound and its deacetylated derivative were assigned by H and C NMR spectroscopy.     

Improved Industrial Syntheses of Penciclovir and Famciclovir Using N2-Acetyl-7-Benzylguanine and a Cyclic Side Chain Precursor

We have established practical synthetic methods for penciclovir (PCV, 1) and famciclovir (FCV, 2) from N2-acetyl-7-benzylguanine (NAc7BnG, 3) and 6,6-dimethyl-5,7-dioxaspiro[2.5]octane-4,8-dione (4)—the latter being a more easily prepared cyclic precursor of the diacetate side chain (5) used in the conventional process. The coupling of 4 with 3 proceeded regioselectively at the N9 position of guanine in good yield. The coupling product was then successfully transformed into the known antiviral agents in a short number of steps.     

Nucleosides,XLVI1 Syntheses and Reactions of 6- and 7-p-Chlorophenyllumazine Nucleosides

Abstract

The syntheses of 6-(4) and 7-p-chlorphenyl-1-(2,3,5-tri-O-benzoyl-β-D-ribofuranosyl)-lumazine (6), was well as the debenzoylation to the corresponding free nucleosides 5 and 7, were improved. Thiation of 4 and 6 by P₄S₁₀ led in excellent yields to 4-thiolumazine nucleosides (8, 10) which could be deblocked to 9 and 11 and converted on treatment with ammonia into the isopterin-N-1- ribofuranosides 13 and 14. 2,2′-Anhydro-nucleoside formation worked well with 5 and 7 respectively to give 15 and 16, which formed on acid hydrolysis the 6- and 7-substituted 1-β-D-arabinofuranosyl-lumazines 18 and 19. The new nucleosides have been characterized by UV and ¹H-NMR spectra.     

SYNTHESIS AND BASE PAIRING PROPERTIES OF 9-DEAZAPURINE N7-NUCLEOSIDES IN OLIGONUCLEOTIDE DUPLEXES AND TRIPLEXES

The 9-deazaguanine N⁷-2′-deoxyribofuranoside (3) as well as the bromo and iodo derivatives 4a,b were synthesized and incorporated in oligonculeotide duplexes and triplexes. Their base pairing properties were investigated and compared with those of the parent purine N⁷-2′-deoxyribofuanosides.     

Preparation of N 2, N 2'7-Trimethylguanosine Affinity Columns

Abstract

2,2,7-trimethylguanosine (TMG) binding proteins from human cells were purified through TMG-affinity columns. TMG synthesis was improved and the TMG obtained was shown to be similar to the TMG in the 5′ cap of the UsnRNAs. The eluates obtained with TMG-affinity chromatographies were very different from those isolated with m⁷G-affinity columns, thus suggesting that specific TMG-binding proteins were obtained. The fraction may be enriched with factors associated with import and/or hypermethylation of UsnRNPs.     

The Synthesis of RNA Containing the Modified Nucleotides N 2-Methylguanosine and N 6, N 6-Dimethyladenosine

Abstract

The phosphoramidites of the naturally occurring modified nucleotides N ²-methylguanosine and N ⁶,N ⁶-dimethyladenosine were synthesized and incorporated into short oligoribonucleotides. Described are the syntheses of the phosphoramidites and the procedures used to deprotect oligoribonucleotides in which the O ⁶ of m²G is protected with a 2-(p-nitrophenyl)ethyl group.     

N6-Alkylthiomethyl and N6-Arylthiomethyl Derivatives of Adenosine and Their Cytokinin Activity

Five new derivatives of adenosine, N⁶-[(1-methylethyl)thiomethyl]-(1), N⁶-methyithiomethyl-(2), N⁶-phenylthiomethyl-(3), N⁶-[(3-amino-3-carboxypropyl)thiomethyl]-(4), and N⁶-[(2-amino-2-carboxyethyl)thiomethyl]adenosine (5), were synthesized and their cytokinin activity was tested in the Amaranthus betacyanin assay and the soybean callus growth.

1, 2, and 3 were active in the former assay and all five compounds were active in the latter assay. The activities of the compounds were, however, weaker than those of the reference derivatives, in which Sulfides were replaced by methylenes, N⁶-isopentyl-, N⁶-n-propyl-, N⁶-benzyl-, and N⁶-(5-amino-5-carboxypentyl)adenosine. This fact indicates that the sulfide structure introduced into the N⁶-side chains had the effect of reducing cytokinin activity.     

Aflatoxin B1 and DNA Adducts. Proposed Model for Surface Noncovalent and Covalent Complexes with N(7) of Guanine. II.

Abstract

An alternate model for surface noncovalent and surface covalent binding of aflatoxin B₁ to N(7) of guanine in DNA is proposed. This model considers the out-of-plane motions of C(8) of aflatoxin B₁ in those interactions.

The covalent intercalated fit of aflatoxin B₁ into DNA arises from steric adjustments made by DNA at the covalent intercalation site as well as local strain in the bond angles about N(7) of guanine and C(8) of aflatoxin B₁. The bond angle about N(7) deviates modestly from the sp² value toward the sp³ value.

This study suggests that the surface covalent aflatoxin B₁ -DNA complex serves only a minor role in aflatoxin's precarcinogenic interaction with DNA and is a likely correctable error.     

Synthesis and Triplex Forming Properties of an Acyclic N7-Glycosylated Guanine Nucleoside

Abstract

A chiral acyclic nucleoside, one in which the ribose carbohydrate has been replaced with a glycerol-based linker, is prepared by glycosylating guanine at the N⁷-nitrogen. The stereochemically pure derivative is converted to a DMT-protected phosphoramidite for incorporation into DNA sequences. Sequence containing the acyclic N⁷-dG nucleoside are capable of forming DNA triplexes in which it is likely that the N¹-H and N²-amino groups of the N⁷-dG are involved in recognition of the guanine base in G-C base pairs.     

Interaction ofN-acetyl-4-, 7-, 8- or 9-deoxyneuraminic acids andN-acetyl-4-, 7- or 8-mono-epi- and-7,8-di-epineuraminic acids withN-acetylneuraminate lyase

Various deoxy- and epi-derivatives ofN-acetylneuraminic acid were synthesized and tested for their substrate properties withN-acetylneuraminate lyase fromClostridium perfringens.N-Acetyl-9-deoxyneuraminic acid is a good substrate,N-acetylneuraminic acid derivatives with epimeric configuration at C-7, C-8 or both are cleaved slowly, whileN-acetyl-4-epi-,N-acetyl-4-deoxy-,N-acetyl-7-deoxy-andN-acetyl-8-deoxyneuraminic acid are resistant to enzyme action.N-Acetyl-4-deoxyneuraminic acid andN-acetyl-4-epineuraminic acid competitively inhibit the enzyme. These studies give further insight into a mechanism proposed for the reversible cleavage of sialic acids byN-acetylneuraminate lyase.     

Determination of N6-Threoninocarbonyladenosine,N2, N2-Dimethylguanosine,Pseudouridine and Other Ribonucleosides in Human Breast Milk

Abstract

Seven modified ribonucleosides from degraded tRNA and rRNA were quantified in milk from mothers with preterm infants. The amounts of N⁶-threoninocarbonyladenosine, N², N²-dimethylguanosine and pseudouridine supplied in the milk have been estimated and related to the respective urinary amounts excreted by preterm infants.     

Synthesis of Base-Modified Oligonucleotides Containing 6- and 7-Aryl Lumazines

Abstract

6-Phenyl, 7-phenyl, 6-(4-biphenyl)-, 7-(4-biphenyl)lumazine N¹-(2′-deoxy-D-ribofuranosides) were synthesized and incorporated in the different positions of self-complementary oligodeoxyribonucleotides, and the influence of modifications on the melting points of duplexes was studied.     

Protonation and quaternization of 1, N6-ethenoadenosine: What are the species responsible for the fluorescence of 1, N6-ethenoadenosine?

Methylation of 1,N⁶-ethenoadenosine (εAdo) gives a mixture of N1- and N9-quaternized methyl-3-β-D -ribofuranosylimidazo[2,1-i] purinium salts (m¹εAdo⁺ and m⁹εAdo⁺, respectively). The ratio of the two forms of the protonated εAdo [H¹εAdo⁺]/[H⁹εAdo⁺] has been estimated to be approximately 0.10 by comparing the uv absorption spectra of the protonated species of εAdo and the two nontautomerizable model compounds. In relation to a study on the protonation effect on the fluorescence of εAdo, we have now determined the effect of quaternization on the fluorescence spectra at 293 and 77 K. We have found that m¹εAdo⁺ and m⁹εAdo⁺ are both fluorescent, and the high degree of coincidence between the fluorescence spectra of εAdo and m¹εAdo⁺ at pH 7 is noted. The m¹εAdo⁺ singlet form is a more efficient fluorescer than the m⁹εAdo⁺ ion at room temperature (quantum yields of 0.43 and 0.11, respectively). All the results which are presented in this paper are consistent with the picture that there exist more than one species responsible for the fluorescence of εAdo, depending on the environment of the molecule in aqueous solution (temperature and pH of solvent).     

Oligonucleotides Containing N7-Cyanoborane-2′-deoxyguanosine

Abstract

For synthesis of N⁷-cyanoborane-containing oligonucleotides, the 5′-DMT protecting group is not a suitable precursor because the boronated nucleoside is incompatible with DMT cations released during deprotection of the oligonucleotide. As an alternative to DMT, we have investigated use of the 5′-Fmoc protecting group. We found that the cyanoborane group is stable during synthesis and deprotection conditions used with Fmoc derivatives.     

Synthesis of new N,N′-bis[1-aryl-3-(piperidine-1-yl)propylidene]hydrazine dihydrochlorides and evaluation of their cytotoxicity against human hepatoma and breast cancer cells

Abstract

N,N′-Bis[1-aryl-3-(piperidine-1-yl)propylidene]hydrazine dihydrochlorides were synthesized by the reaction of 2 mols of 1-aryl-3-(piperidine-1-yl)-1-propanone hydrochlorides with 1?mol of hydrazine hydrate. Aryl part was C₆H₅ (P1), 4-CH₃C₆H₄ (P2), 4-CH₃OC₆H₄ (P3), 4-HOC₆H₄ (P4), 4-ClC₆H₄ (P5), 3-CH₃OC₆H₄ (P6), 4-FC₆H₄ (P7) and 4-BrC₆H₄ (P8). Except P1, all compounds were reported for the first time. The chemical structures were confirmed by UV, ¹H NMR, ¹³C NMR and HRMS spectra. P1, P2, P7 and P8 against human hepatoma (Huh7) cells and P1, P2, P4, P5, P6, P7 and P8 against breast cancer (T47D) cells have shown cytotoxicity. P1, P2 and P7 had more potent cytotoxicity against Huh7 cells than the reference compound 5-FU, whereas only P2 was more potent than the 5-FU against T47D cells. Representative compound P7 inhibited the mitochondrial respiration at 144, 264 and 424?µM concentrations dose-dependantly in liver homogenates. The results suggest that P1, P2, P7 and P8 may serve as model compounds for further synthetic studies.     

B7-H1和B7-H4在口腔鳞状细胞癌组织中的表达及临床意义

目的:探讨口腔鳞状细胞癌(Oral Squamous Cell Carcinoma,OSCC)中B7-H1和B7-H4的表达及其临床意义,并为OSCC的临床诊断、治疗、判断预后及预防等提供依据。方法:采用免疫组织化学S-P法检测B7-H1及B7-H4在60例OSCC及20例非肿瘤患者正常口腔黏膜组织(NOM)中的表达情况,分析两者与OSCC临床病理特征的相关性。结果:B7-H1在OSCC组织中表达显著高于在NOM组织中表达(29例,48.3%v4例,20%,x~2=4.969,P0.05);B7-H4在OSCC组织中表达亦显著高于在NOM组织中表达(31例,51.7%v5例,25%,x~2=4.310,P0.05)。B7-H1与B7-H4在OSCC组织的表达都与TNM分期、淋巴结转移和肿瘤分化程度显著相关(P0.05),而与年龄、性别及肿瘤直径大小等无关。OSCC组织中B7-H1和B7-H4的高表达呈显著性正相关性(x~2=5.613 P0.05),60例组织中B7-H1和B7-H4共表达现象有11例(18.3%),NOM中未发现两者共表达现象。结论:B7-H1和B7-H4过表达与OSCC发生、发展及预后有关,可以作为预后指标。     

Metabolism of 1,N6-Ethenoadenosine

The metabolic fate of 1,N⁶-ethenoadenosine (I) has been studied in rat. The predominant metabolic pathway is the scission of the glycosidic bond in I to yield the free base, 1,N⁶-ethenoadenine (III). Incubation of I with the extract of sarcoma-180 cells in presence of ATP and Mg²⁺ did not result in phosphorylation of the nucleoside. No significant uptake of this compound was observed in L-1210 mouse leukemia cells grown in culture.     

Effects of N7-methylation, N7-platination, and C8-hydroxylation of guanine on H-bond formation with cytosine: platinum coordination strengthens the Watson-Crick pair

d ₆, applying concentration-dependent ¹H NMR spectroscopy: 9-ethylguanine, 7,9-dimethylguanine (7,9-DimeGH⁺), and 7,8-dihydro-8-oxo-9-methylguanine (8-O-9-MeGH), as well as three 9-ethylguanine complexes carrying different Pt(II) moieties at the N7 position. The association constants K for the Watson-Crick pairing schemes are by a factor 2–3 higher in the cases of platinated guanine complexes compared to the Watson-Crick pair between 9-ethylguanine and 1-methylcytosine (K=6.9±1.3 M⁻¹). Similar enhanced stabilities are observed for the pairs formed between 1-MeC and 7,9-DimeGH⁺ or 8-O-9-MeGH. The increase in N1H acidity of the guanine derivative upon modification at the N7 or C8 positions can be correlated with the association constants K; the result is a bell-shaped curve meaning that acidification initially stabilizes hydrogen bond formation up to a certain maximum; further acidification then leads to a destabilization. For two of the examples studied in solution, hydrogen bonding according to Watson-Crick between N7-platinated 9-ethylguanine and 1-methylcytosine has also been established by X-ray crystallography. Received: 29 December 1999 / Accepted: 15 February 2000     

Harmonic Analysis of the Fluorescence Response of Bimane Adducts of Colicin E1 at Helices 6, 7, and 10

The pre-channel state of helices 6, 7, and 10 (Val⁴⁴⁷–Gly⁴⁷⁵ and Ile⁵⁰⁸–Ile⁵²²) of colicin E1 was investigated by a site-directed fluorescence labeling technique. A total of 44 cysteine variants were purified and covalently labeled with monobromobimane fluorescent probe. A variety of fluorescence properties of the bimane fluorophore were measured for both the soluble and membrane-bound states of the channel peptide, including the fluorescence emission maximum, fluorescence anisotropy, and membrane bilayer penetration depth. Using site-directed fluorescence labeling combined with our novel helical periodicity analysis method, the data revealed that helices 6, 7, and 10 are separate amphipathic α-helices with a calculated periodicity of T = 3.34 ± 0.08 for helix 6, T = 3.56 ± 0.03 for helix 7, and T = 2.99 ± 0.12 for helix 10 in the soluble state. In the membrane-bound state, the helical periodicity was determined to be T = 3.00 ± 0.15 for helix 6, T = 3.68 ± 0.03 for helix 7, and T = 3.47 ± 0.04 for helix 10. Dual fluorescence quencher analysis showed that both helices 6 and 7 adopt a tilted topology that correlates well with the analysis based on the fluorescence anisotropy profile. These data provide further support for the umbrella model of the colicin E1 channel domain.     

Backbone and sidechain 1H, 15N and 13C assignments of the NLRP7 pyrin domain

The resonance assignments of the human NLRP7 PYD domain have been determined based on triple-resonance experiments using uniformly [¹³C,¹⁵N]-labeled protein. This assignment is the first step towards the 3D structure determination of the NLRP7 PYD domain.