Synthesis of Branched-Chain and Bicyclic Thiosugar Nucleosides

Abstract

The synthesis of strategically protected nucleosides bearing β-mercaptoethyl chains at the α-C-3′ position from 1,2-di-O-acetyl-2′-S-acetyl-5-t?butyldiphenylsilyl-3-deoxy-3-C-(2′-mercaptoethyl)-α-D-ribofuranose 1 is described. It was found that treatment of the 5-O-methanesulfonyl sugar 19 or nucleoside 5 with either benzylmercaptan or methoxide resulted in rapid cleavage of the thiolester followed by intramolecular cyclization. This was used to prepare the novel trans?fused oxathiahydrindane nucleosides 7 and 27 as well as the cAMP analogue 29.     

Synthetic Studies on the Acyclic Nucleosides of 5-Substituted-6-Azauracils

Abstract

A number of acyclic nucleosides have been prepared. 5-substituted-6-azauracils were persilylated with HMDS and then alkylated with aliphatic side chains e.g., (2-acetoxyethoxy)methyl bromide, 1,3-dibenzuloxy-2-chloromethoxypropane, (1-benzyloxy-3-phthalimido-2-propoxy)methyl chloride, and 1-benzyloxy-2-chloro-methoxybutane to yield protected acyclic nucleosides which were deprotected by Lewis acid or palladium to give various 6-azauracil acyclonucleosides.     

Synthetic Approach to D-Psicofuranosyl Nucleosides and Their 1-Deoxy Analogues

Abstract

The sugar moiety of ketofuranosyl nucleosides derived from D-psicofuranose and 1-deoxy-D-psicofuranose are readily available through nucleophilic addition of D-ribono-1,4 -lactone with lithiated reagents.     

Synthetic and Antiviral Studies of Carboacyclic 6- and 2,6-Substituted Purine Nucleosides

Abstract

Chiral purine derivatives containing a carboacyclic chain mimicking the ribose ring, but lacking the C(3′)-C(4′) bond have been prepared from (2S, 3R)-3-amino-1,2,6-tribenzyloxyhexane 15. The synthesis of this amine via an hex-2-enopyranoside utilizes the absolute configuration defined by carbons 4 and 5 of D-glucose. None of these compounds exhibited any antiviral activity against HIV.     

Conformational Studies on Nucleosides with Furanose Ring Modifications. 1.

Abstract

Conformational energy calculations have been presented on adenine and thymine nucleosides in which the furanose ring is replaced by 2′,3′-dideoxy-2′,3′-didehydrofuran using molecular mechanics and conformational analysis. Conformational energies have been evaluated using the MM2 and AMBER94 force field parameters at two different dielectric constants. The results are presented in terms of isoenergy contours in the conformational space of the glycosidic (χ) and C4′-C5′ (γ) bonds torsions. In general, the χ-γ interrelationships exhibit similarities with the corresponding plots for unmodified nucleosides and nucleotides, reported previously. Consistency of the calculated preferred conformations with the X-ray data is sensitive to the force field employed.     

Synthetic Studies on Guanofosfocin: Glycosylation of 8-Oxo-purine Nucleosides via Mitsunobu Reaction

Abstract

In model studies directed to the total synthesis of guanofosfocins, a unique glycosidic bond formation between the 8-oxo-purine nucleosides and mannopyranose derivatives under Mistunobu conditions is described.     

Synthetic and Antiviral Studies on Certain Acyclic Nucleosides of 5-Benzyl-6-Azauracil Derivatives

Abstract

Several 5-(4-substituted benzyl)-6-azauracils have been synthesized from the corresponding benzaldehydes. The 5-benzyl-6-azauracils were silylated with hexamethyldisilazane and then glycosylated with aliphatic halides, e.g., (2-acetoxyethoxy)methyl bromide and 1,3-dibenzyloxy-2-chloromethoxypropane, to give protected acyclic nucleosides which were deprotected to afford acyclonucleosides of 5-(4-substituted benzyl)-6-azauracils. None of the compounds exhibited significant antiviral activity against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) in vitro.     

Synthetic Approaches to Rare 2-Substituted Purine Nucleosides

Abstract

The syntheses of several novel functional1zed 2-subst1tuted purine nucleosides are described. Key reactions In these transformations Include photolnduced reductive dehalogenatlon, radical deamlnatlon-halogenatlon, and functional1zed carbon-carbon bond formation Involving palladium catalysis. An Interesting ring opening reaction of 2-iodopur1ne nucleoside to an Imidazole derivative under S_RN conditions is mentioned. High-f1eld ¹³C NMR data suggest that the 2-subst1tuted purine nucleosides prefer the anti conformation 1n solution. Biological evaluation of these compounds is currently being carried out.     

Nucleosides Containing Selenium1 II

Abstract

The chemistry of nucleoside analogs with antiviral and antitumor activity is well known. These properties have prompted considerable attention to new developments in synthetic methodology, especially in the field of modification of heterocyclic functions. One such class of methods is introduction of sulfur and selenium into the purine or pyrimidine bases. While thio-substituted nuclesides, are well known, their selenium counterparts are relatively less known in contrast to their potential importance as antitumor agents, as has been reported. The fact that the chemistry of selenium nucleosides is relatively unexplored encouraged review of the literature in this field.     

Synthetic,Structural, and Conformational Studies of Methylated Ring-Expanded Nucleosides Containing the Ihidazo[4, 5-e][1, 4]Diazepine Ring System

Abstract

Syntheses of 4- and 7-methyl 4, 5, 7, 8-tetrahydro-6H-3-(β-ribofuranosyl)imidazo[4, 5-e] [1, 4]diazepine-5, 8-dione, 3 and 1, respectively, are reported. Single-crystal X-ray diffraction analysis of the aglycon of 3 aided in confirming the site of methylation in 3, and that of 4 in elucidating the solid state conformation of 4. Solution conformations of 3 and 4, along with their parent nucleoside 1 and the latter's 1-glycosyl regioisomer 2, were investigated by NOE and CD measurements.     

Nucleosides,XLIV1 Synthesis,Properties and Biological Activity of Indazole Nucleosides

Abstract

Various new haloindazole-1-β-D-ribofuranosides (10-17,20,21) and a 2-β-D-ribofuranoside (18) have been synthesized by the fusion method and by direct halogenations, respectively. The new nucleosides have been characterized by UV and ¹H NMR spectra as well as pK_a determinations. Indazole ribofuranosides behave in aqueous acid like purine and benzimidazole nucleosides showing the same mechanism of cleavage of the glycosidic bonds. Toxicity studies against various cell populations indicate only little biological activities.     

A Convenient Synthesis of D-Psicofuranosyl Nucleosides1

Abstract

As part of our studies on the synthesis of conformationally restricted nucleosides of types 1 and 2, where X = CH₂, O or S, we required access to differentially substituted D-psicofuranosyl nucleosides such as 3. As shown in the table, we have developed a convenient approach to such compounds that depends on the direct condensation of the 1,2:3,4-di-O-isopropylidene-β-D-psicofuranose derivative 4 with an appropriate silylated purine or pyrimidine base.² Although the α and β anomers of 3 are formed in a 1:1 ratio, the yields of the β anomers are generally comparable with earlier condensation methods that use psicofuranosyl- halide², 2-benzoates⁴ or 2-nitro derivative⁵. However, the present method has the advantage that the starting sugar 4 is more readily accessible. The precursor 6′-alcohol can be prepared in very large amounts from D-fructose using the method of Prisbe et al.⁴     

Synthetic Studies on Rotenoids

A new synthetic method of (±)-munduserone has been developed.     

Studies on Synthetic Nucleotides

A direct synthetic method of adenine nucleotides has been described. Treatment of adenine with 2,3-di-O-benzoyl-5-diphenylphosphoryl-d-ribofuranosyl bromide in acetonitrile at 40°C, followed by removal of the protecting groups gave AMP and 3-iso-AMP. The structure and configuration in glycosidic center of the latter was established by UV and NMR spectral studies. Furthermore, treatment of 3-iso-AMP with 5′-nucleotidase gave the nucleoside, which is identical with 3-isoadenosine in its physical properties.     

Synthetic Studies on Dehydrorotenone

The condensation of acetylsalicylchloride with the morpholine enamine of cyclohexanone in the presence of triethylamine gave an adduct which was converted into tetrahydroxanthone (X) by treating with aqueous pyridine containing piperidine. The reaction was applied to condensation of the pyrrolidine enamine (VI) of 6,7-dimethoxychroman-3-one with acetyl tubaic acid chloride to afford dehydrorotenone (II).     

Synthetic Studies on Rotenoids

A general cyclization reaction to dehydrorotenoids has been developed. Dehydrorotenone (III) and dehydrodeguelin (IV) were obtained in high yield from methyl derrisate (Vb) and methyl deguelate (VIb), respectively, by treatment with sodium ethoxide.     

Studies on Synthetic Pyrethroid

Methyl αδ-dimethylsorbate, when submitted to the selective oxidation sequence by the actions of perbenzoic acid, mineral acid, lead tetraacetate and peracetic acid in this order, finally gives β-monomethyl mesaconate, which is converted after hydrolysis to mesaconic acid of the well-defined trans-configuration. The reaction sequence involves no process likely to invert the configuration, and thus another cogent chemical evidence for the trans-configuration of αδ-dimethylsorbic acid is obtained in agreement with the physico-chemical conclusion, previously reported.     

Synthetic Studies on C-Nucleosides

Chenopodium album has a non-photosynthetic chlorophyll protein known as the water-soluble chlorophyll (Chl)-binding protein (WSCP). The C. album WSCP (CaWSCP) is able to photoconvert the chlorin skeleton of Chl a into a bacteriochlorin-like skeleton. Reducing reagents such as β-mercaptoethanol or dithiothreitol inhibit photoconversion, indicating that S–S bridge(s) in CaWSCP are quite important for it. Recently, we found that the mature region of CaWSCP contains five cysteine residues; Cys2, Cys30, Cys48, Cys63, and Cys144. To identify which cysteine residues are involved in the photoconversion, we generated five mutants (C2S, C30S, C48S, C63S, and C144S) by site-directed mutagenesis. Interestingly, C48S, C63S, and C144S mutants showed the same Chl-binding activity and photoconvertibility as those of the recombinant wild-type CaWSCP-His, while the C2S and C30S mutants completely lost Chl-binding activity. Our findings indicated that the S–S bridge between Cys2 and Cys30 in each CaWSCP subunit is essential for Chl-binding activity.     

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.