Nucleosides. IX. Synthesis of Purine N 3,5′‐Cyclonucleosides and N 3,5′‐Cyclo‐2′,3′‐seconucleosides via Mitsunobu Reaction as TIBO‐like Derivatives

The Mitsunobu reaction was applied to prepare, in one step, purine N ³,5′‐cyclonucleosides 10a–d. A subsequent ring opening in the ribose moiety of the resultant N ³,5′‐nucleosides by sodium periodate led to the corresponding N ³,5′‐cyclo‐2′,3′‐seconucleosides. These products consist of 5‐, 6‐, and 7‐membered tricyclic system which is the basic skeleton of TIBO derivatives, known antiviral agents.     

Improved and Reliable Synthesis of 3′‐Azido‐2′,3′‐dideoxyguanosine Derivatives

An improved synthesis of N²‐protected‐3′‐azido‐2′,3′‐dideoxyguanosine 20 and 23 is described. Deoxygenation of 2′‐O‐alkyl (and/or aryl) sulfonyl‐5′‐dimethoxytritylguanosine coupled with [1,2]‐hydride shift rearrangement gave protected 9‐(2‐deoxy‐threo‐pentofuranosyl)guanines ( 10 , 12 and 16 ). This rearrangement was accomplished in high yield with a high degree of stereoselectivity using lithium triisobutylborohydride (l‐Selectride®). Compounds 10 , 12 and 16 were transformed into 3′‐O‐mesylates ( 18 and 21 ), which can be used for 3′‐substitution. The 3′‐azido nucleosides were obtained by treatment of 18 and 21 with lithium azide. This procedure is reproducible with a good overall yield.     

Increased Cytotoxicity of 2′,2′‐Difluoro‐2′‐Deoxycytidine in Human Leukemic Cell‐Lines After a Preincubation with Cyclopentenyl Cytosine

The in vitro modulating effect of Cyclopentenyl cytosine (CPEC) on the metabolism of gemcitabine was studied in lymphocytic and myeloid leukemic cell‐lines. In MOLT‐3 cells, that were pretreated with CPEC, the incorporation of 2′,2′‐difluoro‐2′‐deoxycytidine triphosphate (dFdCTP) into DNA was significantly increased by 57–99% in comparison with cells that were only treated with gemcitabine. The increased incorporation of dFdCTP into DNA in CPEC pretreated cells was paralleled by an increase in apoptotic and necrotic cells of 17–34%. In HL‐60 cells that were preincubated with CPEC, increased concentrations of the mono‐/di‐ and triphosphate form of gemcitabine were observed, as well as an increased incorporation of dFdCTP into DNA (+ 773%). This increased incorporation was paralleled by a significant increase in apoptosis and necrosis. We conclude that CPEC enhances the incorporation of dFdCTP into DNA and thus increases the cytotoxicity of gemcitabine in lymphocytic and myeloid leukemic cell‐lines.     

Design,Efficient Synthesis,and Anti‐HIV Activity of 4′‐C‐Cyano‐ and 4′‐C‐Ethynyl‐2′‐deoxy Purine Nucleosides

Some 4′‐C‐ethynyl‐2′‐deoxy purine nucleosides showed the most potent anti‐HIV activity among the series of 4′‐C‐substituted 2′‐deoxynucleosides whose 4′‐C‐substituents were methyl, ethyl, ethynyl and so on. Our hypothesis is that the smaller the substituent at the C‐4′ position they have, the more acceptable biological activity they show. Thus, 4′‐C‐cyano‐2′‐deoxy purine nucleosides, whose substituent is smaller than the ethynyl group, will have more potent antiviral activity. To prove our hypothesis, we planned to develop an efficient synthesis of 4′‐C‐cyano‐2′‐deoxy purine nucleosides (4′‐CNdNs) and 4′‐C‐ethynyl‐2′‐deoxy purine nucleosides (4′‐EdNs). Consequently, we succeeded in developing an efficient synthesis of six 2′‐deoxy purine nucleosides bearing either a cyano or an ethynyl group at the C‐4′ position of the sugar moiety from 2′‐deoxyadenosine and 2,6‐diaminopurine 2′‐deoxyriboside. Unfortunately, 4′‐C‐cyano derivatives showed lower activity against HIV‐1, and two 4′‐C‐ethynyl derivatives suggested high toxicity in vivo.     

Nucleosides and Nucleotides. 139. Stereoselective Synthesis of (2′S)-2′-C-Alkyl-2′-deoxyuridines

Abstract

A synthetic method for (2′S)-2′-C-alkyl-2′-deoxyuridines (9) has been described. Catalytic hydrogenation of 1-[2-C-alkynyl-2-O-methoxalyl-3,5-O-TIPDS-β-D-arabino-pentofuranosyl]uracils (5) gave 1-[2-C-(2-alkyl)-2-O-methoxalyl-3,5-O-TIPDS-β-D-arabino-pentofuranosyl]uracils (4) as a major product, which were then subjected to the radical deoxygenation, affording (2′S)-2′-alkyl-2′-deoxy-3′,5′-O-TIPDS-uridines (7) along with a small amount of their 2′R epimers.

     

C1′ Acylated Derivatives of 2′-Deoxyuridine. Photolabile Precursors of 2′-Deoxyuridin-1′-yl

Abstract

ABSTRACT

C1′ acylated derivatives of 2′-dcoxyuiidinc (1a-c) were synthesised from 1-[3-deoxy-β-D-psieofiiraiiosylliii.acil (6). The acyl group is introduced via the C1′ aldehyde (11). Following nucleophilic addition, the ketones (1a-c) are obtained via periodinane oxidation and desilylation with NH₄F.     

Nucleosides and Nucleotides. 232. Synthesis of 2′-C-Methyl-4′-thiocytidine: Unexpected Anomerization of the 2′-Keto-4′-thionucleoside Precursor

The synthesis of 2′-C-methyl-4′-thiocytidine (16) is described. Since the 2′-keto-4′-thiocytidine derivative 2β unexpectedly isomerized to 2α and the methylation of 2β proceeded predominantly from the less hindered α-face to give 7, the desired product 16 was synthesized via the Pummerer reaction of the sulfoxide 14 and N ⁴ -benzoylcytosine.     

Nucleosides and Nucleotides. 125. Synthesis and Biological Evaluation of 2′,3′-Dideoxy-3′-fluoro-2′-methylidene Pyrimidine Nucleosides

Abstract

Reaction of 2′-deoxy-2′-methylidene-5′-O-trityluridine (1) with diethylamino-sulfur trifluoride (DAST) in CH₂Cl₂ resulted in the formation of a mixture of (3′R)-2′,3′-dideoxy-3′-fluoro-2′-methylidene derivative 3 and 2′,3′-didehydro-2′,3′-dideoxy-2′-fluoromethyl derivative 4 (3:4 = 1:1.5) in 65% yield. A similar treatment of 1-(2-deoxy-2-methylidene-5-O-trityl-β-D-threo-pentofuranosyl)uracil (19) with DAST in CH₂Cl₂ afforded (3′S)-2′,3′-dideoxy-3′-fluoro-2′-methylidene derivatives 20 and 4 in 38% and 17% yields respectively. Transformation of the uracil nucleosides 4, 12, and 20 into cytosines followed by deprotection furnished the corresponding cytidine derivatives 29, 18, and 25, respectively. The corresponding thymidine congener 27 was also synthesized in a similar manner. All of the newly synthesized nucleosides were evaluated for their inhibitory activities against HIV and for their antiproliferative activities against L1210 and KB cells.     

Conformationally Locked Nucleoside Analogs. Synthesis of 2′-Deoxy-2′-C, 4′-C-Bridged Bicyclic Nucleosides

Abstract

1-α-Methylarabinose was converted, in three steps, to 2-deoxy-2-methyleneribose derivative 3, which was subjected to hydroboration to give 2-α-hydroxymethyl derivative 4 exclusively. 4 was converted to 2,4-bis(hydroxymethyl)ribose derivative 6 in four steps. Mesylation, detritylation, and ring closure, followed by hydrolysis of the mesyl group at O5, gave 3,6-dioxabicyclo[3,2,1]octane derivative 8. After acetylation, 8 was coupled with silylated 6-chloropurine to give desired α- and β-bicyclic-sugar nucleosides.     

Effective Anomerisation of 2′‐Deoxyadenosine Derivatives During Disaccharide Nucleoside Synthesis

The formation of a disaccharide nucleoside (11) by O3′‐glycosylation of 5′‐O‐protected 2′‐deoxyadenosine or its N ⁶‐benzoylated derivative has been observed to be accompanied by anomerisation to the corresponding α‐anomeric product (12). The latter reaction can be explained by instability of the N‐glycosidic bond of purine 2′‐deoxynucleosides in the presence of Lewis acids. An independent study on the anomerisation of partly blocked 2′‐deoxyadenosine has been carried out. Additionally, transglycosylation has been utilized in the synthesis of 3′‐O‐β‐d‐ribofuranosyl‐2′‐deoxyadenosines and its α‐anomer.     

Molecular orbital studies on nucleoside antibiotics,VII. Conformation of 2′-amino- 2′-deoxyguanosine

Conformational properties of the nucleoside antibiotic 2-amino-2-deoxyguanosine have been investigated by the PCILO method along with those of its parent nucleoside, guanosine. This antibiotic, formed by replacement of the 2-hydroxyl group by an amino group in guanosine, shows anti-tumor activity and also inhibits RNA and protein syntheses. Both C(2)-endo and C(3)-endo sugar conformations have been considered in the computations. The results indicate striking similarity between the conformations of the antibiotic and the parent nucleoside, particularly in simulated aqueous environment. The biological implication of this result in terms of the antibiotic activity is discussed.     

Synthesis and Some Properties of Modified Oligonucleotides. II. Oligonucleotides Containing 2′-Deoxy-2′-fluoro-β-D-arabinofuranosyl Pyrimidine Nucleosides

Abstract

In order to find the effects of unnatural nucleosides on the stability of duplex, several oligonucleotides containing 1-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)-uracil(FAU),-cytosine (FAC) and -thymine (FMAU) were synthesized by two alternative approaches: phosphoramidite method on an ABI 392 synthesizer and H-phosphonate procedure on our GeneSyn I universal module synthesizer. It was shown from the melting profiles that the presence of FMAU has a large stabilizing effect on the duplex. Replacement of thymidine with FAU, or deoxycytidine with FAC resulted in the formation of less stable duplexes. Temperature-dependent CD spectroscopy demonstrated that the structures of the fluorine containing oligomers are very similar to those of unmodified oligomers.     

Biological Activity and Phosphorylation of 2′-Azido-2′-Deoxyuridine and 2′-Azido-2′-Deoxycytidlne

Abstract

2′-Azido-2′-deoxyuridine and 2′-azido-2′-deoxycytidine were evaluated for their inhibitory activity against ribonucleotide reductase and for subsequent cell growth inhibition. Their mono-and di-phosphates were synthesized and their inhibitory activities against the reductase were also determined in a permeabilized cell system, along with the two nucleosides. The results of the present study identify the first phosphorylation step involved in the conversion of the two azidonucleosides to the corresponding diphosphates to be rate-limiting in the overall activation.     

Synthesis of D‐Altritol Nucleosides with a 3′‐O‐Tert‐Butyldimethylsilyl Protecting Group

Four D‐altritol nucleosides with a 3′‐O‐tert‐butyldimethylsilyl protecting group are synthesized (base moieties are adenine, guanine, thymine and 5‐methylcytosine). The nucleosides are obtained by ring opening reaction of 1,5:2,3‐dianhydro‐4,6‐O‐benzylidene‐D‐allitol. Optimal reaction circumstances (NaH, LiH, DBU, phase transfer, microwave irridation) for the introduction of the heterocycles are base‐specific. For the introduction of the 3′‐O‐silyl protecting group, long reaction times and several equivalents of tert‐butyldimethylsilyl chloride are needed.     

Synthesis and Antiviral Activity of Novel Fluorinated 2′,3′‐Dideoxynucleosides

A series of 5‐(trifluoroethoxymethyl)‐2′,3′‐dideoxyuridines and 5‐[bis(trifluoroethoxy)‐methyl]‐2′,3′‐dideoxyuridines have been prepared and screened for antiviral activity. The conformations of these compounds are discussed on the bases of NOE studies and the MO calculations. Modelling and NOE studies suggest both syn‐ and anti conformations for these 5‐(2,2,2‐trifluoroethoxymethyl)‐ and 5‐[bis(2,2,2‐trifluoroethoxy)‐methyl]‐ derivatives. The NOE parameters are also suggested to be more attributable to the nature of the fluorine atom than to structural or conformational changes. Compounds 17, 26 and 30 showed some activity in anti‐HIV‐1 and anti‐HIV‐2 assays, but the compounds were devoid of activity against HSV and human rhinovirus. The compounds tested exhibited low cytotoxicity and were inactive against a bank of cancer cells in vitro.     

TheS,X-acetals in nucleoside chemistry. I. The synthesis of 2′- and 5′-O-methylthiomethylribonucleosides

Ribonucleoside 2′- and 5′-O-methylthiomethyl derivatives were synthesized from selectively protected nucleosides by the action of a dimethyl sulfoxide-acetic anhydride-acetic acid mixture.     

Polynucleotides. LII1 Synthesis and properties of poly(2′-deoxy-2′-fluoroadenylic acid)

2′-Deoxy-2′-fluoroadenosine was chemically transformed to its 5′-diphosphate and polymerized with polynucleotide phosphorylase to give poly(2′-deoxy-2′-fluoroadenylic acid) [poly(Af)]. Polymerization proceeded smoothly as in the case of poly(A) and the yield of the polymerization was 55%. The UV absorption spectra of poly(Af) closely resembled those of poly(A) and the hypochromicity was 32% at pH 7.0. The CD profile at 25° and neutrality showed similar pattern to that of other poly(2′-deoxy-2′-halogenoadenylic acids) with somewhat larger [θ] values both in the positive and negative maxima. Acid titration of poly(Af) showed a transition point at pH 5.2 and the Tm of the acid form was 37° which was significantly lower than that of poly(A), but similar to that of poly(2′-azido-2′-deoxyadenylic acid). Poly(Af) formed 1:1 and 1:2 complexes with poly-(U) having Tm of 49° and 62° at 0.04M and 0.15M Na⁺ concentration, respectively. Poly(Af) also formed a 1:2 complex with poly(I) and its Tm was 36° at 0.05M Na⁺ concentration. These data showed that poly(Af) has rather similar properties to those of poly(A), but not to poly(dA).     

N2-Substituted-2′-deoxyguanosine 5′-Triphosphates as Substrates for E. coli DNA Polymerase I

Abstract

Several N²-alkyl and N²-phenyl 2′-deoxyguanosine 5′-triphosphates and 2-bromo-2′-deoxyinosine 5′-triphosphate were synthesized and tested as substrates for E. coli DNA polymerase I with a template: primer system requiring incorporation of 85 nucleotides. N²-Methyl-dGTP and N²-ethyl-dGTP were found to be efficiently incorporated in place of dGTP to give full length product. N²-n-Hexyl-dGTP supported limited full length synthesis at high concentration, but N²-phenyl- and N²-(p-n-butylphenyl)-dGTP were poor substrates. 2-Bromo-2′-deoxyinosine 5′-triphosphate was a good substrate for pol I, and it was a replacement only for dGTP. Melting temperatures of oligodeoxyribonucleotides containing N²-alkyl-dG residues, annealed to complementary single stranded DNA, were lower than that of the normal oligomer.