核糖核苷酸和核糖核苷的N-羧酰咪唑选样性酰化

应用N-羧酰咪唑在合适的条件下可按制备性规模进行选择性地酰化核糖核苷酸和核糖核苷, 得率为50-80%. 对反应机制作了初步探讨.     

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 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.     

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.     

An effective and convenient synthesis of cordycepin from adenosine

Cordycepin is a purine nucleoside analog with potent and diverse biological activities. Herein, we designed two methods to synthesize cordycepin. One method mainly converted the 3′-OH group into an iodide group and further dehalogenation to yield the final product. Although this method presented a short synthetic procedure, the synthesis had a low overall yield, resulting in only 13.5% overall yield. To improve the overall yield of cordycepin, another synthetic route was studied, which consisted of four individual steps: (1) 5′-OH protection (2) esterification (3) -O-tosyl (-OTs) group removal (4) deprotection. The key step in the synthetic method involved the conversion of 5′-O-triphenylmethyladenosine to 3′-O-tosyl-5′-O-triphenylmethyladenosine, using LiAlH₄ as reducing agent. The main advantages of this route were an acceptable total product yield and the commercial availability of all starting materials. The optimal reaction conditions for each step of the route were identified. The overall yield of cordycepin obtained from adenosine as the starting material was 36%.     

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.     

Synthesis of (5R)- and (5S)-5-Methyl-5, 6-dihydrouridine Derivatives

The hydrogenation of 2′, 3′-O-isopropylidene-5-methyluridine (1) in water over 5% Rh/Al₂O₃ gave (5 R)- and (5 S)-5-methyl-5, 6-dihydrouridine (2) , separated as 5′-O-(p-tolylsulfonyl)- (3) and 5′-O-benzoyl- (5) derivatives by preparative TLC. on silica gel and ether/hexane developments. The diastereoisomeric differentiation at the C(5) chiral centre depends upon the reaction media and the nature of the protecting group attached to the ribosyl moiety. The synthesis of iodo derivatives (5 R)- and (5 S)- 4 is also described. The diastereoisomers 4 were converted into (5 R)- and (5 S)-2′, 3′,-O-isopropylidene-5-methyl-2, 5′-anhydro-5, 6-dihydrouridine (7) .     

Selective N3- and 5′-O-Alkylation of 2′,3′-O-isopropylideneuridine with methyl iodide

The 2′,3′-O-isopropylideneuridine ( 1 ) reacts with MeI in the presence of an excess of NaH in THF giving 2′,3′-O-isopropylidene-5′-O-methyluridine ( 2 ). Prolonged reaction time gives rise to 2′,3′-O-isopropylidene-3,5′-O-dimethyluridine ( 4 ). The use of an equimolar amount of base and alkylating agent results predominantly in methylation at N(3) (→ 3).     

The synthesis of ribonucleotide-5′-(5-Iodoindol-3-ol) and (4-methylcoumarin-7-ol) esters for the histochemical demonstration of nucleases

The syntheses of ribonucleotide-5′ monoesters with 5-iodoindol-3-ol and 5′-uridylic acid and 5′-adenylic acid monoesters with 4-methylcoumarin-7-ol has been accomplished by the reaction of phosphorodichloridates with various 2′,3′-O-isopropylidene ribonucleosides, followed by hydrolysis and anion exchange chromatography.     

Über Pterinchemie. 85. Mitteilung. Polyacetylierte 5,6,7,8-Tetrahydro-D- und -L-neopterine. Ein besonderer Fall von N(5)-Alkylierung des 5,6,7,8-Tetrahydroneopterin-Gerüstes

Polyacetylated 5,6,7,8-Tetrahydro-D - and L -neopterins. A Special Case of N(5)-Alkylation of 5,6,7,8-Tetrahydroneopterins Improved conditions are reported for the preparation of the earlier described (6R)- and (6S)-1′-O,2′-O,3′-O,2-N,5-pentaacetyl-5,6,7,8-tetrahydro-L -neopterins, one of which could be obtained as pure crystals. Its structure, determined by X-ray-diffraction analysis, corresponds to the (6R)-enantiomer. The method has also been used to make the corresponding D -diastereoisomers. Further acetylation of (6RS)-1′-O,2′-O,3′-O,2-N-tetraacetyl-5,6,7,8-tetrahydro-D -neopterin under drastic conditions yields a mixture of several polyacetylated D -neopterin derivatives and a polyacetylated ethyl-tetrahydro-D -neopterin which was isolated in crystalline form and established by X-ray-diffraction analysis to be (6R)-1′-O,2′-O,3′-O,4-O,2-N,2-N,8-heptaacetyl-5-ethyl-5,6,7,8-tetrahydro-D -neopterin.     

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 of porphyrinyl-nucleosides

Several porphyrinyl-nucleosides were prepared in the reaction of the OH group of one, two or four meso-p-hydroxyphenyl substituents of porphyrin with 5′-O-tosylates of 2′,3′-O-isopropylidene-adenosine or -uridine, or 5′-O-tosylthymidine; the remaining porphyrin meso-substituents were p-tolyl, p-hydroxyphenyl or 4-pyridyl. The following porphyrinyl-nucleosides were obtained with 8–17% yield: meso-di(p-tolyl)di(p-phenylene-5′-O-2′,3′-O-isopropylidene-adenosine) (or -uridine)porphyrins 1,2 , the respective meso-tetranucleosideporphyrins 3,4 -meso-mono(p-phenylene-5′-O-thymidine)porphyrins 5–7 , meso-di(p-tolyl)di(p-phenylene-5′-O-thymidine)porphyrins 8,9 and the meso-di(p-hydroxyphenyl)di(p-phenylene-5′-O-thymidine)porphyrins 10. Other compounds prepared belonged to the series: meso(4-pyridyl)_4?n(p-phenylene-5′-O-2′,3′-O-isopropylideneuridine)_nporphyrin, n = 1, 2 or 4, 11–13. N-Methylation gave the water soluble iodide salts: (N-methyl-4-pyridinium)4_4?n(p-phenylene-5′-O-2′,3′-isopropylideneuridine)_nporphyrins, n = 1, 2 or 4, 14–16. The ms fab showed in most cases stepwise detachment of the CH₂(5′)-nucleoside fragments. The porphyrins meso disubstituted by thymidine represent a convenient substrate for the build-up of both nucleoside units into the oligo/polynucleotide chains.     

Synthesis of 5-Methyluridine and Its 5′-Mercapto-, 2-Amino-, and 4′,5′-Unsaturated Analogues

The stereospecific cis-hydroxylation of 1-(2,3-dideoxy-β-D -glyceropent-2-enofuranosyl)thymine (1) into 1-β-D -ribofuranosylthymine (2) by osmium tetroxide is described. Treatment of 2′,3′-O, O-isopropylidene-5-methyl-2,5′-anhydrouridine (8) with hydrogen sulfide or methanolic ammonia afforded 5′-deoxy-2′,3′-O, O-isopropylidene-5′-mercapto-5-methyluridine (9) and 2′,3′-O, O-isopropylidene-5-methyl-isocytidine (10) , respectively. The action of ethanolic potassium hydroxide on 5′-deoxy-5′-iodo-2′,3′-O, O-isopropylidene-5-methyluridine (7) gave rise to the corresponding 1-(5-deoxy-β-D -erythropent-4-enofuranosyl)5-methyluracil (13) and 2-O-ethyl-5-methyluridine (14) . The hydrogenation of 2 and its 2′,3′-O, O-isopropylidene derivative 4 over 5% Rh/Al₂O₃ as catalyst generated diastereoisomers of the corresponding 5-methyl-5,6-dihydrouridine ( 17 and 18 ).     

Ein neuer Zugang zu 2′‐O‐(2‐Methoxyethyl)ribonucleosiden ausgehend von D‐Glucose

A New Access to 2′‐ O ‐(2‐Methoxyethyl)ribonucleosides Starting from D ‐Glucose A new synthesis of 2′‐O‐(2‐methoxyethyl)ribonucleosides, building blocks for second‐generation antisense oligonucleotides, starting from D ‐glucose is presented. The key‐step is the transformation of 3‐O‐methoxyethylallofuranose to 2‐O‐(2‐methoxyethyl)ribose by NaIO₄ oxidation. Together with the 4′‐phenylbenzoyl protecting group, which results in crystalline intermediates, this synthesis provides an easy and cheap access to 2′‐O‐(2‐methoxyethyl)‐substituted ribonucleosides.     

Nucleotides Part XL. Synthesis and Characterization of Modified 2′–5′ Adenylate Trimers–Potential Antiviral Agents

2′–5′ Adenylate trimers 41–44 carrying the (tert-butyl)dimethylsilyl (tbds) group at the 3′-OH position of various sugar moieties were synthesized via the phosphoramidite method. The use of the (tert-butyloxy)carbonyl (boc) and 2-(4-nitrophenyl)ethylsulfonyl (npes) groups for 2′-OH protection in neighbourhood to the 3′-O-tbds residue was compared during the synthesis of the target trimers. For other functional positions, the use of the 2-(4-nitrophenyl)ethyl (npe) and 2-(4-nitrophenyl)ethoxycarbonyl (npeoc) blocking groups were favoured.     

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.     

Nucleotide Coupling in Reverse Micelles

Nucleotide coupling was investigated in reverse micelles formed by (cetyl)trimethylammonium bromide (CTAB), in hexane/pentan-1-o1. In particular, the coupling of 2′ -deoxy-5′-O-methylcytidine 3′ O-phosphate, prepared by phosphoramidite chemistry, with 5′-amino-5-deoxythymidine was studied in the presence of a H₂O-soluble carbodiimide at (w_o) = 11 and 22 (w_o=[H₂O]/[CTAB]). The effect of w_o on the reaction rate was investigated. A solid-phase strategy was developed for the synthesis of 2′-deoxy-5′O-methyl-cytidyl-(3′-5′)-5′-amino-5′deoxythymidine. The nucleotide coupling yieldig the expected product occurred readily in reverse micelles. Nucleotide coupling is thus possible in reverse micelles, and this is discussed in connection with the micellar self-replication program.     

Regioselective Transformations of 2′,3′-Seconucleosides into Anhydro Structures and Chiral Crown Ethers

Intramolecular cyclisation of properly protected and activated derivatives of 2′,3′-secouridine ( = 1-{2-hydroxy-1-[2-hydroxy-1-(hydroxymethyl)ethoxy]-ethyl}uracil; 1 ) provided access to the 2,2′-, 2,3′-, 2,5′-, 2′,5′-, 3′,5′-, and 2′,3′-anhydro-2′,3′-secouridines 5, 16, 17, 26, 28 , and 31 , respectively (Schemes 1–3). Reaction of 2′,5′-anhydro-3′-O-(methylsulfonyl)- ( 25 ) and 2′,3′-anhydro-5′-O-(methylsulfonyl)-2′,3′-secouridine ( 32 ) with CH₂CI₂ in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene generated the N(3)-methylene-bridged bis-uridine structure 37 and 36 , respectively (Scheme 3). Novel chiral 18-crown-6 ethers 40 and 44 , containing a hydroxymethyl and a uracil-1-yl or adenin-9-yl as the pendant groups in a 1,3-cis relationship, were synthesized from 5′-O-(triphenylmethyl)-2′,3′-secouridine ( 2 ) and 5′-O,N⁶-bis(triphenylmethyl)-2′,3′-secoadenosine ( 41 ) on reaction with 3,6,9-trioxaundecane-1,11-diyl bis(4-toluenesulfonate) and detritylation of the thus obtained (triphenylmethoxy) methylcompound 39 and 43 , respectively (Scheme 4).     

Novel Selectivity in Carbohydrate Reactions Ii. Selective 6-O-Glycosylation of a Partially Protected Lactoside 1 2

Abstract

A novel regioselectivity was observed in the silver salt promoted glycosylation of 2-(trimethylsilyl)ethyl 3′-O-benzyl-β-D-lactoside using acetobromogalactose as the glycosyl donor. The resulting trisaccharide, obtained in 67% yield, was shown to have the newly formed β-glycosidic linkage at the O-6 position of the lactoside. This was confirmed by synthesis of the authentic product by an alternate route. The novel regioselectivity observed is attributed to the presence of the axially disposed 4′-OH group in the lactoside acceptor.

     

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).