Enzymatic separation of epimeric 4-C-hydroxymethylated furanosugars: Synthesis of bicyclic nucleosides

• Neha Rana,
• Manish Kumar,
• Vinod Khatri,
• Jyotirmoy Maity and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2017, 13, 2078–2086, doi:10.3762/bjoc.13.205

• : bicyclonucleosides; biocatalysis; lipase; Novozyme®-435; separation of epimers; Introduction Sugar-modified bicyclic nucleosides have drawn the attention of synthetic chemists because of their effect on the conformational restriction of the furanose moiety of the nucleoside [1][2][3][4][5][6][7][8][9]. The

• conformational restriction has led to the enhancement in target selectivity and in vivo stability of the nucleoside-based drug candidates. One of the important precursors for the synthesis of different types of bicyclonucleosides is 4-C-hydroxymethyl-1,2-O-isopropylidene-α-D-ribofuranose. The synthesis of the

• sulfonate (TMS-triflate) in acetonitrile yielded the triacetylated nucleoside 8 in 94% yield. Subsequently, deacetylation of acetoxy groups in nucleoside 8 with 2 M NaOH solution in water/dioxane (1:1) also led to the concomitant cylization between suitably placed C-3′-OH and C-1′′-tosyl groups to afford 3

Effect of uridine protecting groups on the diastereoselectivity of uridine-derived aldehyde 5’-alkynylation

• Raja Ben Othman,
• Mickaël J. Fer,
• Laurent Le Corre,
• Sandrine Calvet-Vitale and
• Christine Gravier-Pelletier

Beilstein J. Org. Chem. 2017, 13, 1533–1541, doi:10.3762/bjoc.13.153

• ; nucleoside; protecting groups; uridine; Introduction Nucleoside and nucleotide derivatives or analogues are biologically active compounds of major interest [1][2]. Their widespread applications span from therapeutic agents, such as antibacterial [3][4][5], antiviral [6] or antitumor [7][8] drugs, to

• numerous approaches, this 5′ stereogenic center comes from the chiral pool and the nucleobase is introduced under Vorbrüggen conditions [20][21][22][23][24][25][26]. It can also be created directly on the nucleoside, either by functionalization of an alkene at C-5’ [27][28][29][30][31][32] or by the

• organometallic reagents onto nucleoside aldehyde (Table 1), we decided to investigate the influence of the protecting groups of the uridine aldehyde on the stereochemical outcome of the nucleophilic addition of a Grignard reagent and we wish to report herein the results of our study. Results and Discussion We

Synthesis of oligonucleotides on a soluble support

• Harri Lönnberg

Beilstein J. Org. Chem. 2017, 13, 1368–1387, doi:10.3762/bjoc.13.134

• order by esterification of phosphoric acid with the 3´-OH of one and the 5´-OH of the other nucleoside. Usually, the 3´-OH is first esterified with an appropriate derivative of phosphoric acid and the resulting building block is then reacted with the 5´-OH (Figure 1). Either a linear or a convergent

• protected nucleoside 3´-(2-cyanoethyl-N,N-dialkylphosphoramidite)s (1 in Scheme 1) or 3´-(H-phosphonate)s are usually preferred as building blocks [3] (2 in Scheme 1). The attacking 5´-OH apart, all other nucleophilic functionalities must be kept protected during the coupling. The primary amino groups of

• derivatives 2-ethyl- and 2-benzylthiotetrazole [8] or 4,5-dicyanoimidazole [9]. The activator has a dual role donating a proton to the departing dialkylamino group and attacking as an anionic species on phosphorus [10]. Nucleoside H-phosphonates are, in turn, converted in situ to reactive mixed anhydrides

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• nucleosides [23][24]. The enzymes typically employed for these purposes are nucleoside phosphorylases (NPs) or nucleoside deoxyribosyltransferases (NDTs) in the presence of inorganic phosphate in a tandem enzymatic process [25]. In Scheme 5 we highlight a very recent example of this methodology for the

First total synthesis of kipukasin A

• Chuang Li,
• Haixin Ding,
• Zhizhong Ruan,
• Yirong Zhou and
• Qiang Xiao

Beilstein J. Org. Chem. 2017, 13, 855–862, doi:10.3762/bjoc.13.86

• subsequent Vorbrüggen glycosylation, the protecting group could be removed smoothly in the presence of 5 mol % Ph3PAuOTf in dichloromethane to provide kipukasin A in high yield and regioselectivity. Keywords: gold catalysis; kipukasin A; marine nucleoside; total synthesis; Vorbrüggen glycosylation

• , ester protection is preferred for Vorbrüggen glycosylations in nucleoside syntheses. Very recently, ortho-alkynylbenzoate was successfully developed by our group as neighboring participation group to synthesize 2’-modified nucleosides [24], which could be removed smoothly in the presence of gold(I

• ) [36]. With glycosylation donor 16 in hand, we proceeded to investigate the crucial Vorbrüggen glycosylation with uracil (4). To our delight, in a similar manner as our described in [17], it proved to be efficient to give nucleoside 17 with exclusive β-configuration in 89% yield. At last, using our

Synthesis of ribavirin 2’-Me-C-nucleoside analogues

• Fanny Cosson,
• Aline Faroux,
• Jean-Pierre Baltaze,
• Jonathan Farjon,
• Régis Guillot,
• Jacques Uziel and
• Nadège Lubin-Germain

Beilstein J. Org. Chem. 2017, 13, 755–761, doi:10.3762/bjoc.13.74

• carbon atom in the 2’-position are an indium-mediated alkynylation and a 1,3-dipolar cyclization. Keywords: alkynylation; antiviral; cancer; C-nucleosides; ribavirin; Introduction The triazole nucleoside ribavirin (RBV, Figure 1) is used for the treatment of a number of viral infections and may be

• the combination, due to its particular role. Recently, we developed an alkynyl glycosylation protocol allowing us to obtain C-nucleoside derivatives and we turned our attention to ribavirin C-nucleoside analogues. Moreover, recently De Clerq [13] outlined the potential of C-nucleosides in the arsenal

N-Propargylamines: versatile building blocks in the construction of thiazole cores

• S. Arshadi,
• E. Vessally,
• L. Edjlali,
• R. Hosseinzadeh-Khanmiri and
• E. Ghorbani-Kalhor

Beilstein J. Org. Chem. 2017, 13, 625–638, doi:10.3762/bjoc.13.61

• prevent gout flare-ups [5][6][7]. Ritonavir (norvir), is an HIV protease inhibitor. It works by blocking the growth of HIV [8][9]. Tiazofurin is a C-nucleoside analogue with antineoplastic activity and acts by inhibition of the guanosine triphosphate (GTP) biosynthesis through a reduction of PI and PIP

Synthesis of 1-indanones with a broad range of biological activity

• Marika Turek,
• Dorota Szczęsna,
• Marek Koprowski and
• Piotr Bałczewski

Beilstein J. Org. Chem. 2017, 13, 451–494, doi:10.3762/bjoc.13.48

• as antiviral and antibacterial agents [5] (I and II), anticancer drugs [6] (VI), pharmaceuticals used in the Alzheimer’s disease treatment [7] (III), cardiovascular drugs [7] (IV), insecticides, fungicides, herbicides [8] (V) and non-nucleoside, low molecular drugs for the hepatitis C treatment

Revaluation of biomass-derived furfuryl alcohol derivatives for the synthesis of carbocyclic nucleoside phosphonate analogues

• Bemba Sidi Mohamed,
• Christian Périgaud and
• Christophe Mathé

Beilstein J. Org. Chem. 2017, 13, 251–256, doi:10.3762/bjoc.13.28

• carbocyclic nucleoside methylphosphonate analogues bearing purine bases (adenine and guanine) was accomplished using bio-sourced furfuryl alcohol derivatives. All compounds were prepared using a Mitsunobu coupling between the heterocyclic base and an appropriate carbocyclic precursor. After deprotection, the

• compounds were evaluated for their activity against a large number of viruses. However, none of them showed significant antiviral activity or cytotoxicity. Keywords: analogue; antiviral; carbocyclic; nucleoside; phosphonate; Introduction Biomass is a valuable resource in search of renewable organic carbon

• also the source of 4-hydroxy-2-cyclopentenone, which, in enantiopure form, has been used as an intermediate for the synthesis of natural products and pharmaceutical drugs [3]. Recently, racemic (+/−)-4-hydroxy-2-cyclopentenone has found application in the synthesis of nucleoside analogues [4][5] and

A postsynthetically 2’-“clickable” uridine with arabino configuration and its application for fluorescent labeling and imaging of DNA

• Heidi-Kristin Walter,
• Bettina Olshausen,
• Ute Schepers and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2017, 13, 127–137, doi:10.3762/bjoc.13.16

• structure of double-helical DNA elucidates that the positioning of the fluorophores in the major groove may be improved by inversion of the configuration at the 2’-position of the anchor nucleoside sugar. In fact, arabino nucleic acids are an important class of antisense oligonucleotides [20] since their

• functions of nucleoside 3 were selectively protected by the Markiewicz silyl ether [22]. The central step of the whole synthetic procedure was the alkylation of the 2’-OH function of nucleoside 4 by propargylic bromide which worked in 65% yield in the presence of NaH as base. After removal of the silyl

• protecting group from nucleoside 5, the 5’-position of nucleoside 2 was again protected by 4,4’-dimethoxytrityl chloride (DMTr-Cl) and, finally, the 3’-position of nucleoside 6 was phosphitylated. Remarkably, the overall yield of phosphoramidite 7 with the optimized conditions over the described five steps

Nucleophilic displacement reactions of 5′-derivatised nucleosides in a vibration ball mill

• Olga Eguaogie,
• Patrick F. Conlon,
• Francesco Ravalico,
• Jamie S. T. Sweet,
• Thomas B. Elder,
• Louis P. Conway,
• Marc E. Lennon,
• David R. W. Hodgson and
• Joseph S. Vyle

Beilstein J. Org. Chem. 2017, 13, 87–92, doi:10.3762/bjoc.13.11

• University, Department of Chemistry, Lower Mountjoy, Stockton Road, Durham DH1 3LE, UK 10.3762/bjoc.13.11 Abstract Vibration ball-milling in a zirconia-lined vessel afforded clean and quantitative nucleophilic displacement reactions between 4-methoxybenzylthiolate salts and nucleoside 5′-halides or 5

• ′-tosylates in five to 60 minutes. Under these conditions, commonly-encountered nucleoside cyclisation byproducts (especially of purine nucleosides) were not observed. Liquid-assisted grinding of the same 5'-iodide and 5′-tosylate substrates with potassium selenocyanate in the presence of DMF produced the

• corresponding 5′-selenocyanates in variable yields over the course of between one and eleven hours thereby avoiding the preparation and use of hygroscopic tetrabutylammonium salts. Keywords: ball mill; chalcogen; mechanochemistry; nucleophilic substitution; nucleoside; Introduction Nucleophilic displacement

Enzymatic synthesis and phosphorolysis of 4(2)-thioxo- and 6(5)-azapyrimidine nucleosides by E. coli nucleoside phosphorylases

• Vladimir A. Stepchenko,
• Anatoly I. Miroshnikov,
• Frank Seela and
• Igor A. Mikhailopulo

Beilstein J. Org. Chem. 2016, 12, 2588–2601, doi:10.3762/bjoc.12.254

• , 6-azathymine and 6-aza-2-thiothymine was studied using dG and E. coli purine nucleoside phosphorylase (PNP) for the in situ generation of 2-deoxy-α-D-ribofuranose-1-phosphate (dRib-1P) followed by its coupling with the bases catalyzed by either E. coli thymidine (TP) or uridine (UP) phosphorylases

• only 5-phenyl- and 5-tert-butyl-6-azauracils displayed very low substrate activity. The role of structural peculiarities and electronic properties in the substrate recognition by E. coli nucleoside phosphorylases is discussed. Keywords: enzymatic glycosylation; PM3 and ab initio calculations

• ; recombinant E. coli uridine, thymidine and purine nucleoside phosphorylases; substrate properties; 4(2)-thioxo- and 6(5)-aza-uacil and -thymine; Introduction Nucleosides of 4- and 2-thioxopyrimidines and 6-azapyrimidines attract much attention from the time of pioneering works in the early 1950s on the

Facile synthesis of a 3-deazaadenosine phosphoramidite for RNA solid-phase synthesis

• Elisabeth Mairhofer,
• Elisabeth Fuchs and
• Ronald Micura

Beilstein J. Org. Chem. 2016, 12, 2556–2562, doi:10.3762/bjoc.12.250

• -amino-3-deazapurine and benzoyl-protected 1-O-acetylribose. The novel path is superior to previously described syntheses in terms of efficacy and ease of laboratory handling. Keywords: deazapurine nucleoside; nucleosidation; protection groups; ribozymes; Introduction The synthesis of 3-deazaadenosine

• mechanisms. Therefore, 1-deazaadenosine (c1A), 1-deaza-2’-deoxyadenosine (c1dA), 3-deazaadenosine (c3A), and 3-deaza-2’-deoxyadenosine (c3dA), and the corresponding phosphoramidites to prepare oligoribonucleotides are highly requested nucleoside modifications. Unfortunately, synthetic approaches to achieve

• them are troublesome and time consuming, in particular for c3A. To the best of our knowledge, only two papers have reported the synthesis of c3A phosphoramidites so far [16][17]. Thereby, the major bottleneck is access to the naked nucleoside. Although the c3A nucleoside is commercially available

Synthesis of medronic acid monoesters and their purification by high-performance countercurrent chromatography or by hydroxyapatite

• Elina Puljula,
• Jouko Vepsäläinen and
• Petri A. Turhanen

Beilstein J. Org. Chem. 2016, 12, 2145–2149, doi:10.3762/bjoc.12.204

• could prove the achieved degree of purity. Some other methods have also been used for the synthesis of nucleoside methylene-BPs which could structurally be considered as medronic acid monoesters [21][22]. Interestingly, there are only a few publications describing the synthesis of medronic acid

Synthesis of the C8’-epimeric thymine pyranosyl amino acid core of amipurimycin

• Pramod R. Markad,
• Navanath Kumbhar and
• Dilip D. Dhavale

Beilstein J. Org. Chem. 2016, 12, 1765–1771, doi:10.3762/bjoc.12.165

• the formation of the pyranose ring skeleton to give 2,7-dioxabicyclo[3.2.1]octane 12. Functional group manipulation in 12 gave 21 that on stereoselective β-glycosylation afforded the pyranosyl thymine nucleoside 2 – a core of amipurimycin. Keywords: amipurimycin; 1,3-anhydrosugar; anti-fungal agent

• ; carbohydrate; peptidyl nucleosides; Introduction Peptidyl nucleoside antibiotics are a class of complex molecules that encompass an extensive array of natural products [1]. The notable structural features of peptidyl nucleosides are responsible for their miscellaneous biological activities such as antitumor

• -dioxabicyclo[3.2.1]octane A could be glycosylated stereoselectively with the requisite nucleobase to give β-nucleoside pyranosyl skeleton 2. The bridged bicyclic system A was visualized from the azido diol B. Thus, hydrolysis of the 1,2-acetonide functionality in B will lead to in situ generation of

Dinuclear thiazolylidene copper complex as highly active catalyst for azid–alkyne cycloadditions

• Anne L. Schöffler,
• Ata Makarem,
• Frank Rominger and
• Bernd F. Straub

Beilstein J. Org. Chem. 2016, 12, 1566–1572, doi:10.3762/bjoc.12.151

• ][22][23][24][25][26], nucleoside, nucleotide, and oligonucleotide chemistry [27][28][29], in fluorogenic reactions [30], and in the syntheses of dendrimers [25][31]. The detailed mechanism of this reaction and the exact role of copper(I) and the species involved in the catalytic cycle had remained

Beta-hydroxyphosphonate ribonucleoside analogues derived from 4-substituted-1,2,3-triazoles as IMP/GMP mimics: synthesis and biological evaluation

• Tai Nguyen Van,
• Audrey Hospital,
• Corinne Lionne,
• Lars P. Jordheim,
• Charles Dumontet,
• Christian Périgaud,
• Laurent Chaloin and
• Suzanne Peyrottes

Beilstein J. Org. Chem. 2016, 12, 1476–1486, doi:10.3762/bjoc.12.144

• “click-fleximer” as expanded nucleobase mimicking the purine [14]. “Click-fleximer” nucleoside analogues are easily accessible derivatives using copper-catalysed alkyne–azide cycloaddition (CuAAC) and this synthetic methodology allows generating a small library of derivatives depending on the nature of

• acids. Thus, nucleoside phosphonate analogues 1a–q (Scheme 2) were isolated as their sodium salts with yields ranging from 21 to 77% over three steps. Structures of all final compounds were unambiguously confirmed on the basis of NMR (1H, 13C and 31P) and MS (MS and HRMS) data analysis (see Supporting

Synthesis of a deuterated probe for the confocal Raman microscopy imaging of squalenoyl nanomedicines

• Eric Buchy,
• Branko Vukosavljevic,
• Maike Windbergs,
• Dunja Sobot,
• Camille Dejean,
• Simona Mura,
• Patrick Couvreur and
• Didier Desmaële

Beilstein J. Org. Chem. 2016, 12, 1127–1135, doi:10.3762/bjoc.12.109

• was extended to other nucleoside analogues such as antiretroviral agents, ddC, ddI and AZT [14] and to siRNA oligonucleotides [15]. More notably, squalenoylation of adenosine and the subsequent formation of NAs, allowed prolonged circulation of this nucleoside, providing neuroprotection in mice with

• when dealing with low drug concentrations or biological-like structures such as peptide drugs or nucleoside analogues. To overcome this issue, deuterium can be introduced to a sample molecule, as it exhibits a significant Raman signal at around 2200 cm−1, which is in a so called “silent region” (1800

The role of alkyl substituents in deazaadenine-based diarylethene photoswitches

• Christopher Sarter,
• Michael Heimes and
• Andres Jäschke

Beilstein J. Org. Chem. 2016, 12, 1103–1110, doi:10.3762/bjoc.12.106

• DNA photoswitches for the application in bionanotechnology and synthetic biology. Keywords: diarylethene; nucleoside; electrocyclic rearrangement; photochromism; photoswitch; Introduction Most biomacromolecules are per se not responsive to light. Their conversion into photoresponsive molecules opens

Muraymycin nucleoside-peptide antibiotics: uridine-derived natural products as lead structures for the development of novel antibacterial agents

• Daniel Wiegmann,
• Stefan Koppermann,
• Marius Wirth,
• Giuliana Niro,
• Kristin Leyerer and
• Christian Ducho

Beilstein J. Org. Chem. 2016, 12, 769–795, doi:10.3762/bjoc.12.77

• natural products. These uridine-derived nucleoside-peptide antibiotics inhibit the bacterial membrane protein translocase I (MraY), a key enzyme in the intracellular part of peptidoglycan biosynthesis. This review describes the structures of naturally occurring muraymycins, their mode of action, synthetic

• replication and folate metabolism [21]. Promising candidates meeting the requirements for new drugs are nucleoside antibiotics, i.e., uridine-derived compounds that address the enzyme translocase I (MraY) as a novel target, thereby interfering with a membrane-associated intracellular step of peptidoglycan

• biosynthesis. This review will focus on muraymycins as a subclass of nucleoside antibiotics, covering their mode of action, synthetic approaches as well as SAR studies on several derivatives. Furthermore, first insights into the biosynthesis of these Streptomyces-produced secondary metabolites will be

Interactions between 4-thiothymidine and water-soluble cyclodextrins: Evidence for supramolecular structures in aqueous solutions

• Vito Rizzi,
• Sergio Matera,
• Paola Semeraro,
• Paola Fini and
• Pinalysa Cosma

Beilstein J. Org. Chem. 2016, 12, 549–563, doi:10.3762/bjoc.12.54

• described in [18], the preparation of simple physical mixtures with CDs was already shown to be effective in terms of protective activity. Starting from these considerations, the main goal of this work is to study the ability of the modified nucleoside S4TdR to form inclusion complexes with five CDs: 2-HP-α

• carefully investigated by some authors of this paper elucidating the behavior of such a nucleoside in aqueous solution. The main form of the nucleoside, absorbing at 337 nm, is the protonated structure reported in Figure 1. The deprotonation, on the nitrogen atom in position 3, started only at pH values

• nucleoside (indicated by an asterisk in Figure 5, in the wavenumber region of 1700–1600 cm−1) changed distinctly. The dip between the two signals is reduced with important variations of the C=O vibration mode. The effect is even stronger with TRIMEB and DIMEB CDs (Figure 5D,E). Moreover, when inclusion

Versatile synthesis and biological evaluation of novel 3’-fluorinated purine nucleosides

• Hang Ren,
• Haoyun An,
• Paul J. Hatala,
• William C. Stevens Jr,
• Jingchao Tao and
• Baicheng He

Beilstein J. Org. Chem. 2015, 11, 2509–2520, doi:10.3762/bjoc.11.272

• University of Chicago Medical Center, Chicago, Illinois 60637, USA 10.3762/bjoc.11.272 Abstract A unified synthetic strategy accessing novel 3'-fluorinated purine nucleoside derivatives and their biological evaluation were achieved. Novel 3’-fluorinated analogues were constructed from a common 3’-deoxy-3

• analogs of natural products nebularine and 6-methylpurine riboside were constructed via our convergent synthetic strategy. Synthesized nucleosides were tested against HT116 (colon cancer) and 143B (osteosarcoma cancer) tumor cell lines. We have demonstrated 3’-fluorine purine nucleoside analogues display

• potent tumor cell growth inhibition activity at sub- or low micromolar concentration. Keywords: anticancer; 3’-fluororibonucleoside; purine nucleoside; 6-substituted purine; synthesis; Introduction Antimetabolites are extremely useful for the treatment of cancers and viral infections and are one of the

Dicarboxylic esters: Useful tools for the biocatalyzed synthesis of hybrid compounds and polymers

• Ivan Bassanini,
• Karl Hult and
• Sergio Riva

Beilstein J. Org. Chem. 2015, 11, 1583–1595, doi:10.3762/bjoc.11.174

• parent compound 12. A similar approach was followed later on by Lin and coworkers, who described the enzymatic esterification of the nucleoside 5-fluorouridine (13) and of other polyhydroxylated bioactive molecules with divinyl esters of dicarboxylic acids [31][32][33][34][35]. The monovinyl esters

Preparation of a disulfide-linked precipitative soluble support for solution-phase synthesis of trimeric oligodeoxyribonucleotide 3´-(2-chlorophenylphosphate) building blocks

• Amit M. Jabgunde,
• Alejandro Gimenez Molina,
• Pasi Virta and
• Harri Lönnberg

Beilstein J. Org. Chem. 2015, 11, 1553–1560, doi:10.3762/bjoc.11.171

• previously shown [26] that the disulfide linkage may be cleaved by reduction with dithiotreitol or TCEP at pH buffered to 7.6 without detritylation taking place. Elongated treatment with TCEP appeared, however, to be too harsh. Evidently, the 5´-terminal nucleoside should be inserted as a more acid tolerant

• support enabled efficient purification of the support-bound intermediates and product by virtually quantitative precipitation from MeOH after each coupling and 5´-O-deprotection. However, on assembling the trimeric 3´-(2-chlorophenyl phosphate) building blocks, the 5´-terminal nucleoside should be

• 2 h to obtain the tetravalent nucleoside cluster 7a, transferred to a stoppered 50 mL plastic tube, and MeOH (46 mL) was added. The precipitate formed was kept at −20 °C overnight, isolated by centrifugation, and dried to give 7a (0.20 g, 70%) as a white solid. The precipitate and supernatant were

Synthesis of novel N-cyclopentenyl-lactams using the Aubé reaction

• Madhuri V. Shinde,
• Rohini S. Ople,
• Ekta Sangtani,
• Rajesh Gonnade and
• D. Srinivasa Reddy

Beilstein J. Org. Chem. 2015, 11, 1060–1067, doi:10.3762/bjoc.11.119

• cyclopentenyl-substituted lactams. Upon dihydroxylation, this affords the N-cyclopentenyl-lactam compounds in racemic form. Given the numerous uses of nucleosides and related compounds, we were interested in the synthesis of carbocylic nucleoside mimics. The attempts and results are described herein. Keywords

• –1.83 (series of multiplets, 5H), 1.74–1.61 (series of multiplets, 3H); 13C NMR (100 MHz, CD3OD) δ 178.6, 73.7, 70.5, 62.6, 61.8, 47.3, 37.5, 37.0, 32.9 29.3, 28.0, 23.0; HRMS calculated for C12H21NO4, [M + Na]+: 266.1363, found 266.1358. Selective carbocyclic nucleoside analogues from the literature