2,4-Disubstituted Pyrrolo[2,3-d]pyrimidine α-D- and β-D-Ribofuranosides Related to 7-Deazaguanosine

Nucleobase-anion glycosylation (KOH, tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1), MeCN) of the pyrrolo[2,3-d]pyrimidines 4a – d with 5-O-[(1,1-dimethylethyl)dimethylsilyl]-2,3-O-(1-methylethylidene)-α-D -ribo-furanosyl chloride ( 5 ) gave the protected β-D -nucleosides 6a – d stereoselectively (Scheme 1). Contrary, the β-D -halogenose 8 yielded the corresponding α-D -nucleosides ( 9a and 9b ) apart from minor amounts of the β-D -anomers. The deprotected nucleosides 10a and 11a were converted into 4-substituted 2-aminopyrrolo[2,3-d]-pyrimidine β-D -ribofuranosides 1 . 10c , 12 , 14 , and 16 and into their α-D -anomers, respectively (Scheme 2). From the reaction of 4b with 5 , the glycosylation product 7 was isolated, containing two nucleobase moieties.     

Stereoselective synthesis of pyrrolo[2,3-d]pyrimidine α- and β-D-ribonucleosides from anomerically pure D-ribofuranosyl chlorides: Solid-Liquid Phase-Transfer Glycosylation and 15N-NMR Spectra

Solid-liquid phase-transfer glycosylation (KOH, tris[2-(2-methoxyethoxy)ethye]amine ( = TDA-1), MeCN) of pyrrolo[2,3-d]pyrimidines such as 3a and 3b with an equimolar amount of 5-O-[(1,1 -dimethylethyl)dimethylsilyl]-2,3-O-(1-methylethylidene)-α-D -ribofuranosyl chloride (1) [6] gave the protected β-D -nucleosides 4a and 4b , respectively, stereoselectively (Scheme). The β-D -anomer 2 [6] yielded the corresponding α-D -nucleosides 5a and 5b with traces of the β-D -compounds. The 6-substituted 7-deazapurine nucleosides 6a , 7a , and 8 were converted into tubercidin (10) or its α-D -anomer (11) . Spin-lattice relaxation measurements of anomeric ribonucleosides revealed that T₁ values of H? C(8) in the α-D -series are significantly increased compared to H? C(8) in the β-D -series while the opposite is true for T₁ of H? C(1′). ¹⁵N-NMR data of 6-substituted 7-deazapurine D -ribofuranosides were assigned and compared with those of 2′-deoxy compounds. Furthermore, it was shown that 7-deaza-2′deoxyadenosine ( = 2′-deoxytubercidin; 12 ) is protonated at N(1), whereas the protonation site of 7-deaza-2′-deoxyguanosine ( 20 ) is N(3).     

Synthesis of New Nucleosides by coupling of chloropurines with 2- and 3-deoxy derivatives of N-methyl-D-ribofuranuronamide

The synthesis of new deoxyribose nucleosides by coupling chloropurines with modified D -ribose derivatives is reported. The methyl 2-deoxy-N-methyl-3-O-(p-toluoyl)-α-D -ribofuranosiduronamide (α-D - 8 ) and the corresponding anomer β-D - 8 were synthesized starting from the commercially available 2-deoxy-D -ribose ( 1 ) (Scheme 1). Reaction of α-D - 8 with the silylated derivative of 2,6-dichloro-9H-purine ( 9 ) afforded regioselectively the N⁹-(2′-deoxyribonucleoside) 10 as anomeric mixture (Scheme 2), whereas β-D - 8 did not react. Glycosylation of 9 or of 6-chloro-9H-purine ( 17 ) with 1,2-di-O-acetyl-3-deoxy-N-methyl-β-D -ribofuranuronamide ( 13 ) yielded only the protected β-D -anomers 14 and 18 , respectively (Scheme 3). Subsequent deacetylation and dechlorination afforded the desired nucleosides β-D - 11 , β-D - 12,15 , and 16 . The 3′-deoxy-2-chloroadenosine derivative 15 showed the highest affinity and selectivity for adenotin binding site vs. A₁ and A_2A adenosine receptor subtypes.     

Nucleotides. Part LIV. Synthesis of condensed N1-(2′-deoxy-β-D-ribofuranosyl)lumazines,New fluorescent building blocks in oligonucleotide synthesis

Various condensed areno[g]lumazine derivatives 2 , 3 , and 5 – 7 were synthesized as new fluorescent aglycones for glycosylation reactions with 2-deoxy-3, 5-di-O-(p-toluoyl)-α/β-D -erythro-pentofuranosyl chloride ( 10 ) to form, in a Hilbert-Johnson-Birkofer reaction, the corresponding N¹-(2′-deoxyribonucleosides) 15 – 21 . The β-D -anomers 15 , 17 , 19 , and 21 were deblocked to 24 – 27 and, together with N¹-(2′-deoxy-β-D -ribofuranosyl)lumazine ( 22 ) and its 6, 7-diphenyl derivative 23 , dimethoxytritylated in 5′-position to 28–33. These intermediates were then converted into the 3′-(2-cyanoethyI diisopropylphosphoramidites) 34 – 39 which function as monomeric building block in oligonucleotide syntheses as well as into the 3′-(hydrogen succinates) 40 – 45 which can be used for coupling with the solid-support material. A series of lumazine-modified oligonucleotides were synthesized and the influence of the new nucleobases on the stability of duplex formation studied by measuring the T_m values in comparison to model sequences. A substantial increase in the T_m is observed on introduction of areno[g]lumazine moieties in the oligonucleotide chain stabilizing obviously the helical structures by improved stacking effects. Stabilization is strongly dependent on the site of the modified nucleobase in the chain.     

Nucleosides. Part LIX. The 2-(4-nitrophenyl)ethylsulfonyl (Npes) Group: A New Type of Protection in Nucleoside Chemistry

The 2-(4-nitrophenyl)ethylsulfonyl (npes) group is developed as a new sugar OH-blocking group in the ribonucleoside series. Its cleavage can be performed in a β-eliminating process under aprotic conditions using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as the most effective base. Since sulfonates do not show acyl migration, partial protection of 1,2-cis-diol moieties is possible leading to new types of oligonucleotide building blocks. A series of Markiewicz-protected ribonucleosides 1–10 is converted into their 2′-O-[2-(4-nitrophenyl)ethylsulfonyl] derivatives 29–38 in which the 5′-O? Si bond can be cleaved by acid hydrolysis forming 39–45 . Subsequent monomethoxytritylation leads to 46–50 , and desilylation affords the 5′-O-(monomethoxytrityl)-2′-O-[2-(4-nitrophenyl)ethylsulfonyl]ribonucleosides 51–55 . Acid treatment to remove trityl groups do also not harm the npes group (→ 56–58 ). Unambiguous syntheses of fully blocked 2′-O-[2-(4-nitrophenyl)ethylsulfonyl]ribonucleosides 96–102 are achieved from the corresponding 3′-O-(tert-butyl)dimethylsilyl derivatives. Furthermore, various base-protected 5′-O-(monomethoxytrityl)- and 5′-O-(dimethoxytrityl)ribonucleosides, i.e. 59–77 , are treated directly with 2-(4-nitrophenyl)ethylsulfonyl chloride forming in all cases a mixture of the 2′,3′-di-O- and the two possible 2′- and 3′-O-monosulfonates 107–148 which can be separated into the pure components by chromatographic methods. The npes group is more labile towards DBU cleavage than the corresponding base-protecting 2-(4-nitrophenyl)ethyl (npe) and 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) groups allowing selective deblocking which is of great synthetic potential.     

Ein neuer Zugang zu 2′-O-Alkylribonucleosiden und Eigenschaften deren Oligonucleotide

A New Access to 2′-O-Alkylated Ribonucleosides and Properties of 2′-O-Alkylated Oligoribonucleotides A general access to 2′-O-alkylated ribonucleosides using the key intermediate 5 is presented. The incorporation of 2′-O-‘ethyleneglycol’- and 2′-O-‘glycerol’-substituted (i.e., 2′-O-(2-hydroxyethyl)- and 2′-O-(2,3-dihydroxypropyl)-substituted) ribonucleosides into oligonucleotides affords a new generation of oligonucleotides with high affinity for RNA, high specificity, and increased nuclease resistance.     

Nucleosides. Part LXI. A Simple Procedure for the Monomethylation of Protected and Unprotected Ribonucleosides in the 2′-O- and 3′-O-Position Using Diazomethane and the Catalyst Stannous Chloride

Intensive studies on the diazomethane methylation of the common ribonucleosides uridine, cytidine, adenosine, and guanosine and its derivatives were performed to obtain preferentially the 2′-O-methyl isomers. Methylation of 5′-O-(monomethoxytrityl)-N²-(4-nitrophenyl)ethoxycarbonyl-O⁶-[2-(4-nitrophenyl)ethyl]-guanosine ( 1 ) with diazomethane resulted in an almost quantitative yield of the 2′- and 3′-O-methyl isomers which could be separated by simple silica-gel flash chromatography (Scheme 1). Adenosine, cytidine, and uridine were methylated with diazomethane with and without protection of the 5′ -O-position by a mono- or dimethoxytrityl group and the aglycone moiety of adenosine and cytidine by the 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) group (Schemes 2–4). Attempts to increase the formation of the 2′-O-methyl isomer as much as possible were based upon various solvents, temperatures, catalysts, and concentration of the catalysts during the methylation reaction.     

Synthesis and Biological Evaluation of 2-(2-Deoxy-β-D-ribofuranosyl)pyridine-4-carboxamide

A new protected 2-deoxy-D -ribose derivative, 5-O-[(tert-butyl)diphenylsilyl]-2-deoxy-3,4-O- isopropylidene-aldehydo-D -ribose ( 5 ), was synthesized starting from 2-deoxy-D -ribose. This compound was coupled with 2-lithio-4-(4,5-dihydro-4,4-dimethyloxazol-2-yl)pyridine giving a D /L -glycero-mixture 7 of 5-O-[(tert-butyl)diphenylsilyl]-2-deoxy-1-C-[4-(4,5 -dihydro-4,4-dimethyloxazol-2-yl)pyridin-2-yl]-3,4-O-isopropylidene- D -erythro-pentitol. The mixture 7 was 1-O-mesylated with methanesulfonyl chloride and subsequently treated with CF₃COOH/H₂O and ammonia to afford the α/β-D -anomers 10 of 2-(2-deoxy-D -ribofuranosyl)pyridine-4-carboxamide. Both anomers were purified and separated by HPLC and identified by NMR and DCI-MS. Anomer β-D - 10 was evaluated against a series of tumor-cell lines and a variety of viral strains. No antitumor or antiviral activity was observed.     

A comparison of two methods for the preparation of 3-Deazapurine ribonucleosides

The reaction of the trimethylsilyl derivative of 4,6-dichloroimidazo[4,5-c]pyridine with 2,3,5-tri-O-benzoyl- D -ribofuranosyl bromide gave four nucleosides-the α- and β-anomers of the 1-isomer and the α- and β-anomers of the 3-isomer (3.9:2.7:1.5:1). In contrast, the fusion reaction of 4,6-dichloroimidazo[4,5-c ]pyridine with 1,2,3,5-tetra-O-acetyl-β- D -ribofuranose gave a high yield of the 1-β-isomer, which was converted to the known 3-deazaadenosine (4-amino-l-β- D -ribofuranosylimidazo[4,5-c]pyridine).     

The relationship between proton–proton NMR coupling constants and substituent electronegativities. II—conformational analysis of the sugar ring in nucleosides and nucleotides in solution using a generalized Karplus equation

The relationship between vicinal NMR proton–proton coupling constants and the pseudorotational properties of the sugar ring in nucleosides and nucleotides is reinvestigated. Compared with our earlier study several important improvements are introduced: first, a new empirical generalization of the classical Karplus equation is utilized, which allows an accurate correction for the effects of electronegativity and orientation of substituents on ³J(HH); second, empirical correlations between the parameters governing the conformation of β-D -furanosides (taken from an analysis of 178 crystal structures) were used to define proton–proton torsion angles as a function of the pseudorotation parameters P and Φ_m; and, third an iterative least-squares computer program was devised to obtain the best fit of the conformational parameters to the experimental coupling constants. NMR data for the sugar ring in the following compounds were taken from the literature and analysed: 3′,5′-cyclic nucleotides, a base-stacked ribonucleotide, 2′-anhydroarabinonucleosides, α-D -2′,2-O-cyclouridine, 2′- and 3′-aminosubstituted ribonucleosides, 2′- and 3′-deoxyribonucleosides. The present results confirm that the conformational properties found in the solid state are, on the whole, preserved in solution.     

Stereoselective Synthesis of Indazole 2′-Deoxy-β-D-ribonucleosides: Glycosylation of the Nucleobase Anion

The glycosylation of indazolyl anions derived from 4a , b with 2-deoxy-3,5-bis-O-(4-methylbenzoyl)-α-D -erythro-pentofuranosyl chloride ( 5 ) is described. The reaction was Stereoselective – exclusive β-D -anomer formation – but regioisomeric N¹- and N²-(2′-deoxy-β-D -ribofuranosides) (i.e. 6a and 7a , resp., and 6b and 7b , resp.) were formed in about equal amounts. They were deprotected to yield 8a , b and 9a , b . Compound 1 , related to 2′-deoxyadenosine ( 3 ), and its regioisomer 2 were obtained from 8b and 9b , respectively, by catalytic hydrogenation. The anomeric configuration as well as the position of glycosylation were determined by 1D NOE-difference spectroscopy. The first protonation site of 1 and 2 was found to be the NH₂ group. The N-glycosylic bond of 1H-indazole N¹-(2′-deoxyribofuranosides) is more stable than that of the parent purine nucleosides. Compound 1 is no substrate for adenosine deaminase.     

Preparation and Transmetallation of a Triphenylstannyl β-D-Glucopyranoside: A highly stereoselective route to β-D-C-glycosides via glycosyl dianions

The triphenylstannyl β-D -glucopyranoside 4 was synthesized in one step from the 1,2-anhydro-α-D -glucopyranose 3 with (triphenylstannyl)lithium (Scheme 1). Transmetallation of 4 with excess BuLi, followed by quenching the dianion 7 with CD₃OD gave (1S)-1,5-anhydro-3,4,6-tri-O-benzyl-[1-²H]-D - glucitol ( 8 ) in 81% yield (Scheme 2). Trapping of 7 with benzaldehyde, isobutyraldehyde, or acroleine gave the expected β-D -configurated products 11, 12 , and 13 in good yields. Preparation of C-acyl glycosides from acid chlorides, such as acetyl or benzoyl chloride was not practicable, but addition of benzonitrile to 7 yielded 84% of the benzoylated product 14 . Treatment of 7 with MeI led to 15 (30%) along with 40% of 18 , C-alkylation being accompanied by halogen-metal exchange. Prior addition of lithium 2-thienylcyanocuprate increased the yield of 15 to 50% and using dimethyl sulfate instead of MeI led to 77% of 15 . No α-D -anomers could be detected, except with allyl bromide as the electrophile, which yielded in a 1:1 mixture of the anomers 16 and 17 .     

Nucleosides and nucleotides. Part 25.. Synthesis of a protected 1-(2′-deoxy-β-D-ribofuranosyl)-1 H-benzimidazole 3′-phosphate

1-(2′-Deoxy-5′-O-dimethoxytrityl-′-D -ribofuranosyl)-1 H-benzimidazole 3′-[(p-chlorophenyl)(2-cyanoethyl) phosphate] ( 6 ) has been synthesized from 1-(β-D -ribofuranosyl)-1H-benzimidazole ( 3b ) using regiospecific 2′-deoxygenation. The latter compound was obtained by glycosylation of benzimidazole with the D -ribose derivative 2 leading exclusively of the β-D -anomer.     

Synthesis of 5′-C- and 2′-O-(Bromoalkyl)-Substituted Ribonucleoside Phosphoramidites for the Post-synthetic Functionalization of Oligonucleotides on Solid Support

The preparation of building blocks for the incorporation of 6′-O-(5-bromopentyl)-substituted β-D -allofuranosylnucleosides and 2′-O-[(3-bromopropoxy)methyl]-substituted ribonucleosides into oligonucleotide sequences is presented (Schemes 1 and 2). These reactive building blocks can be modified with a variety of soft nucleophiles while the (fully protected) sequence is still attached to the solid support. As an example of this strategy, we carried out some preliminary solid-phase substitution and conjugation reactions with DNA sequences containing a 2′-O-[(3-bromopropoxy)methyl]-substituted ribonucleoside (Scheme 3) and determined the pairing properties of duplexes obtained therefrom.     

A Versatile and Convenient Regioselective Acylation of 2′-Deoxynucleosides and Ribonucleosides by Supported Lipases of Pseudomonas Cepacia

Pseudomonas Cepacia lipase supported on ceramic particles (lipase PS-C) and on diatomite (lipase PS-D) regioselectively acylated 2′-deoxynucleosides and ribonucleosides to 3′-O-acetyl-2′-deoxynucleosides and 3′-O-acetyl-ribonucleosides with oxime esters in organic solvents at room temperature. This enzymatic reaction was significant because the regioselectivity was total; as any other regioisomer nor the N-acylated product were observed.     

Synthese von Nucleosiden aus 2-substituierten Imidazolen

Synthesis of 2-Substituted Imidazole Nucleosides Condensation of the trimethylsilyl derivatives of 2-substituted diethyl and dimethyl imidazole-4,5-dicarboxylates ( 3–5 and 7–9 ) with 1-O-acetyl-2,3,5-tri-O-benzoyl-β-D -ribofuranose ( 2 ) in the presence of trimethysilyl trifluoromethanesulfonate provided the 2-substituted diethyl and dimethyl 1-(2′,3′, 5′-tri-O-benzoyl-β-D -ribofuranosyl)imidazole-4, 5-dicarboxylates 10–15 . These were treated with ammonia to afford the 2-substituted 1-(β-D -ribofuranosyl)imidazole-4,5-dicarboxamides 16–21 . Treatment of 2-methyl-( 16 ) and 2-ethyl-1-(β-D -ribofuranosyl)imidazole-4,5-dicarboxamide ( 17 ) with fuming nitric acid in oleum at ?30° yielded the nitric acid esters 23 and 24 . Besides the esterification of the sugar hydroxyl groups one H-atom of the imidazolecarboxamide function at C(5) in these nucleosides was also substituted by the NO₂ group. The conformations in solution of 16 and 23 have been determined by ¹H- and ¹³C-NMR. spectroscopy. These studies indicate that the nucleosides exist in dimethyl-sulfoxide solution preferentially in the S-gg-syn-conformation ( 16 ) and N-gt-conformation ( 23 ). In the crystal structure of nucleoside 23 , the ribose was found to be in the O(1′)_endo, C(1′)_exo twist conformation. The conformation about C(4′), C(5′) is gauche-trans and the molecule exists in the syn form.     

Nucleoside und Nucleotide. Teil 15. Synthese von Desoxyribonucleosid-monophosphaten und -triphosphaten mit 2(1H)-Pyrimidinon, 2(1H)-Pyridinon und 4-Amino-2(1H)-pyridinon als Basen

Nucleosides and Nucleotide. Part 15. Synthesis of Deoxyribonucleoside Monophosphates and Triphosphates with 2(1H)-Pyrimidinone, 2(1H)-Pyridinone and 4-Amino-2(1H)-pyridinone as the Bases The phosphorylation of the modified nucleosides 1-(2′-deoxy-β-D -ribofuranosyl)-2(1 H)-pyrimidinone (M_d, 4 ), 4-amino-1-(2′-deoxy-β-D -ribofuranosyl)-2(1 H)-pyridinone (Z_d, 6 ) and the synthesis of 1–2′-deoxy-β-D -ribofuranosyl-2(1 H)-pyrimidinone-5′-O-triphosphate (pppM_d, 1 ), 1-(2′-deoxy-β-D ribofuranosyl)-2(1 H)-pyridinone-5′-O-triphosphate (pppII_d, 2 ), and 4-amino-1-(2′-deoxy-βD -ribofuranosyl)-2(1 H)-pyridinone-5′-O-triphosphate (pppZ_d, 3 ) are described. The nucleoside-5′-monophosphates pM_d (5) and pZ_d (7) were obtained by selective phosphorylation of M_d (4) and Z_d (6) , respectively, using phosphorylchloride in triethyl phosphate or in acetonitril. The reaction of pM_d (5) pII _d (8) or pZ_d (7) with morpholine in the presence of DCC led to the phosphoric amides 9, 10 and 11 , respectively, which were converted with tributylammonium pyrophosphate in dried dimethylsulfoxide to the nucleoside-5′triphosphates 1, 2 and 3 , respectively.     

The use of the wittig reaction in the modification of purine nucleosides

The Pfitzner-Moffatt oxidation of 6-chloro-9-(2,3-O-isopropylidene-β-D-ribofuranosyl)purine, 9-(2,3-O-isopropylidene-β-D-ribofuranosyl)-6-(methylthio)purine, and 2′,3′-O-isopropylideneadenosine gave the corresponding 5′-aldehydes (3, 13, and 4), which were allowed to react with a number of Wittig ylids. The resulting olefins, primarily trans, were reduced either catalytically or with diimide before removal of the 2′,3′-O-isopropylidene groups to give the desired 5′-substituted purine ribonucleosides.     

Trennung und Charakterisierung von β-Carotin-Isomeren

Separation and Characterization of the cis-Isomers of β,β-Carotene A stable HPLC. system is described allowing the excellent separation of 11 different cis-isomers of β,β-carotene from the all-trans compound. The system is applied to the analysis of cis/trans mixtures obtained from plant extracts and by photoisomerization of the all-trans isomer. Al₂O₃ is used as the stationary phase while hexane with controlled H₂O content is utilized as the mobile phase. With the aid of the optimum conditions 8 sufficiently stable cis isomers were isolated and their structures shown to be the 9-, 13- and 15-cis, the 9,9′-, 9, 13-, 9, 13′- and 13,13′-di-cis and, tentatively, the 9,13,13′-tri-cis β,β-carotenes by application of 270-MHz-FT.-¹H-NMR. spectroscopy.