Synthesis of 5-homologous AZT and D4T derivatives.

The 3'-iodonucleosides 4 have been synthesized by condensation of silylated 5-alkyluracils 2 with methyl 5-O-tert-butyldiphenylsilyl-2,3-dideoxy-3-iodo-D-threo-pentofur anoside (3). 4 was treated with sodium azide and the deprotected nucleoside 5 was subsequently obtained by treatment with tetrabutylammonium fluoride. The nucleoside 4 produced the corresponding 2',3'-didehydro-2',3'-dideoxy nucleoside 6 and 3',4'-didehydro-2',3'-dideoxy nucleoside 7 in elimination reactions on treatment with sodium methoxide.     

Unsaturated didehydrodeoxycytidine drugs. 1. Impact of C=C positions in the sugar ring

The chemical names of a pair of recently synthesized antitumor drugs are given in the present study as 1',2'-didehydro-3',4'-deoxycytidine and 3',4'-didehydro-2',4'-deoxycytidine. The order of stabilities, geometries, and ionization potentials of the unsaturated sugar-modified cytidine derivatives is investigated quantum mechanically. Our density functional theory calculations based on the B3LYP/6-311++G** model reveal that 3',4'-didehydro-2',4'-deoxycytidine (SD-C2) is slightly more stable than its isomer, 1',2'-didehydro-3',4'-deoxycytidine, by an energy of 5.28 kJ x mol(-1) in isolation. The isomers structurally differ by only the C=C location in the sugar ring. However, the compounds exhibit an unusual orientation with a less puckered sugar ring; that is, 3',4'-didehydro-2',4'-deoxycytidine is determined to be a beta-nucleoside, which is a C1'-endo, north conformer with an anticlinal sugar ring, whereas 1',2'-didehydro-3',4'-deoxycytidine is neither an alpha-nucleoside nor a beta-nucleoside but is a C4'-endo, south conformer with an antiperiplanar sugar ring. The present study further indicates that the C=C double bond location imposes significant effects on their ionization potentials (IPs) and other important molecular properties such as molecular electrostatic potential (MEP). In addition, inner shell binding energy spectral variations with respect to the C=C bond exhibit more site dependence. The valence shell binding energy spectral changes are, on the other hand, significant and delocalized. The latter indicates that such changes in valence space are not isolated effects but are within the entire nucleoside. Finally, the present study suggests that the nearly 0.6 eV difference in the first ionization potentials (highest occupied molecular orbital) of the isomers is sufficiently large to identify them by further spectroscopic measures.     

New synthesis of 2',3'-didehydro-2',3'-dideoxynucleosides.

The 3'-iodonucleoside 4 and the 3'-O-methylsulfonylthymidine 9 have been synthesized by condensation of silylated uracils 2 with methyl 5-O-tert-butyldiphensilyl-2,3-dideoxy-3-iodo-D-threo-pentofuran oside (3) and methyl 5-O-tert-butyldiphenylsilyl-2-deoxy-3-methylsulfonyl-D-erythro- pentofuranoside (8), respectively. The nucleoside 4 and 9 produced the corresponding 2',3'-didehydro-2',3'-dideoxynucleosides 5 in an elimination reaction on treatment with sodium methoxide. The compounds 5b showed no antiviral activity against HIV-1.     

New telluride-mediated elimination for novel synthesis of 2',3'-didehydro-2',3'-dideoxynucleosides

Several 2',3'-dideoxynucleosides (ddNs) and 2',3'-didehydro-2',3'-dideoxynucleosides (d4Ns) are FDA-approved anti-HIV drugs. Via conveniently synthesized 2,2'-anhydronucleosides, we have developed a novel synthesis of d4Ns by discovering and applying a new telluride-mediated elimination reaction. Our experiment results show that after substitution of 2,2'-anhydronucleosides with a telluride monoanion, a telluride intermediate is formed, and its elimination leads to formation of the olefin products (d4Ns). Our mechanistic study indicates that this telluride-assisted reaction consists of two steps: substitution (or addition) and elimination. By using dimethyl ditelluride (0.1 equiv) as the reagent, d4Ns can be synthesized with yields up to 90% via this telluride-mediated elimination. Our novel strategy has great potential to simplify synthesis of these drugs and to further reduce cost of AIDS treatment and will also facilitate development of novel d4N and ddN analogues.     

含长碳烷基核苷氢亚磷酸酯衍生物的合成与表征

通过将抗病毒药物核苷(3'-叠氮-2',3'-二脱氧胸苷AZT或2',3'-二脱氢-2',3'-二脱氧胸苷d4T)与三氯化磷反应, 然后在不同的醇解试剂作用下, 一锅法合成得到6个含长链烷基的核苷氢亚磷酸二酯衍生物, 并采用³¹P NMR, ¹H NMR, ¹³C NMR和ESI-MS对其结构进行了表征.     

Novel benzyl rearrangements in electrospray ionization multistage tandem mass spectra of benzyl 2',3'- didehydro-2',3'-dideoxythymidin-5'-yl H-phosphonate

Several alkyl 2',3'-didehydro-2',3'-dideoxythymidin-5'-yl H-phosphonates were synthesized and analyzed by electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). Two kinds of novel benzyl rearrangement reactions were observed in ESI - MS(2) of [M + H](+), [M + Na](+) and [M + K](+) of benzyl 2',3'-didehydro-2',3'-dideoxythymidin-5' yl H-phosphonate. Results from tandem mass spectrometry, high-resolution mass spectrometry and control experiments showed that the benzyl migration could undergo a four-membered cyclic rearrangement reaction, and benzyl was essential in the process.     

De novo synthesis of 4'-ethoxy nucleoside analogues

Butenolides 5a and 13 were used as optically active templates in the de novo synthesis of 4'-disubstituted nucleoside analogues. The butenolides were reduced and acylated in situ to give acetates 10 and 14. Vorbrüggen coupling gave the protected nucleoside analogues 11 and 15. Reduction of 11 gave 4'-ethoxy-2',3'-dideoxythymidine (6) and deprotection of 15 gave 4'-ethoxy-2',3'-dideoxydidehydrothymidine (7). The cis-dihydroxylation of a variety of butenolides occurred with the major product formed from oxidation of the beta-face.     

2'''',3''''-双脱氢-2'''',3''''双脱氧胸苷5''''-亚磷酸苄酯的ESI-MS~n中的一种新颖的重排反应

爱滋病(AIDS)是一种严重威胁人类健康的传染性疾病。研究和开发新的、高疗效的抗AIDS的药物已成了生物学家、化学家和药物学家的主要的研究方向之一。2',3'-双脱氢.2',3'-双脱氧胸苷(d4T)是HIV逆转录酶抑制剂,它们是美国FDA通过的可用于治疗AIDS的一类药物。由于d4T等本身对HIV无活性,只有经细胞代谢成5'-磷酸化产物后才对HIV产生抑制作用,因此很有必要对d4T进行结构改造,而对上述药物的结构进行改造是研制新的抗AIDS的化学药物最简捷的途径。因此,我们合成了一系列的d41、5'-亚磷酸酯的衍生物,并对它们的电喷雾质谱进行了详细的研究。研究发现了2',3'-双脱氢,2',3'双脱氧胸苷(d4T)-5'-氢亚磷酸苄酯的一种新颖的重排反应,并对其机理进行了进一步的研究。有关结果不仅有助于对这类化合物的结构分析,而且对它们的合成、药物性质以及药物代谢等方面的研究都具有重要意义。     

Computational analysis of aza analogues of [2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D-ribofuranose]-3'-spiro-5"-(4"-amino-1",2"-oxathiole-2",2"-dioxide) (TSAO) as HIV-1 reverse transcriptase inhibitors: relevance of conformational properties on the inhibitory activity

We have carried out a theoretical analysis of aza analogues of [2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]-3'-spiro-5"-(4"-amino-1",2"-oxathiole-2",2"-dioxide) by a variety of computational tools, aimed to account for the effect of the endocyclic amino moiety N-2" on the inhibitory activity against HIV-1. Docking studies suggest that compounds substituted at the N-3 and N-2' ' positions present the same binding mode to the [2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]-3'-spiro-5"-(4"-amino-1",2"-oxathiole-2",2"-dioxide)thymine prototype, where the endocyclic amino group remains mostly exposed to the solvent. A careful conformational analysis performed through different theoretical levels, from molecular mechanics to high-level quantum mechanical calculations, provides a rationalization based on conformational preferences, which appears as strongly determined by the substitution at N-2", and on electrostatic effects from the bulk water.     

Identification of amino acid phosphorodiamidates of antiviral nucleosides using electrospray ionization tandem mass spectrometry

Several amino acid phosphorodiamidate derivatives of d4T as anti-HIV prodrugs were synthesized and investigated using electrospray ionization multistage tandem mass spectrometry (ESI-MS(n)). A novel methyl group migration in gas phase was observed in ESI-MS(2) of the sodium adducts of amino acid methyl ester of phosphorodiamidates of 2',3'-didehydro-2',3'-dideoxythymidine (d4T). The proposed structures of the rearrangement ions were confirmed by high resolution tandem mass spectrometry. A possible mechanism involving the pentacoordinate phosphoric-carboxylic phosphate anhydride was proposed, in which a seven-membered ring intermediate was formed by coordination with the metal ion between the phosphoryl group and carbonyl oxygen atom. Thus, the intrinsic properties of phosphoryl group might be the key factors responsible for this migration.     

2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides: synthesis,stereospecificity, some chemical transformations,and conformational analysis

The synthesis of methyl 5-O-benzoyl-2-chloro-2,3-dideoxy-3-fluoro-beta-d-ribofuranoside (5) and its use as a glycosylating agent for persilylated thymine, N(6)-benzoyladenine, and N(4)-benzoylcytosine are described (Scheme 1). The 2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides 10-12 synthesized were transformed to 2',3'-dideoxy-3'-fluoro-alpha- and -beta-d-erythro-pentofuranoside nucleosides of thymine (13a,b), adenine (14a,b), and cytidine (15a,b) by treatment with tributyltin hydride in the presence of alpha,alpha'-azobisisobutyronitrile (Scheme 2). Treatment of 2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides with 1 M MeONa/MeOH under reflux for 1-5 h afforded 2',3'-didehydro-2',3'-dideoxy-2'-chloro-d-pentofuranosyl nucleosides as the principal products (47-81%) of the reaction, along with recovered starting nucleoside (11-33%) (Scheme 3). Easy HF elimination was also observed in the case of the 2'-azido-2',3'-dideoxy-3'-fluoro-beta-d-ribofuranosides of thymine (17) and adenine (20) (Scheme 3). The role of conformational peculiarities of 2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides as well as of 17 and 20 in the observed exclusive elimination of HF is discussed. The conformational analysis of a rather broad palette of 2,3-dideoxy-3-fluoro-2-(X-substituted)-d-ribofuranosides was performed with the aid of the PSEUROT (version 6.3) program, using (i) the recently reparametrized Karplus-type relation (Chattopadhyaya and co-workers. J. Org. Chem. 1998, 63, 4967) and (ii) empirical bond angle correction terms suggested by us. The predictive power of the Brunck and Weinhold model (J. Am. Chem. Soc. 1979, 101, 1700) of the gauche effect between atoms and groups as a conformational driving force acting upon the pentofuranose ring is explored. Their model invokes maximum antiperiplanar sigma <--> sigma stabilization when the donating bond is the least polar one and the acceptor orbital is at the most polarized bond and is found at least as satisfactory, and in various specific cases more so than, as rationalizations on the basis of the preference of the gauche vs the trans conformation of two vicinal electronegative substituents (Wolfe. Acc. Chem. Res. 1972, 5, 102).     

Assignment of the liposidomycin diazepanone stereochemistry

The liposidomycins comprise a family of complex nucleoside antibiotics that inhibit bacterial peptidoglycan synthesis. Their structures (1, 2) feature nucleoside, ribofuranoside, diazepanone, and lipid regions. Several stereogenic centers remain unassigned, including three within the diazepanone region: C-6', C-2'", and C-3'". An intramolecular reductive amination reaction has been used to prepare model diazepanones. Analysis of 40 and two of its diastereomers by NMR spectroscopy, X-ray crystallography, and molecular modeling indicates a close relative configurational and conformational match between 40 and the liposidomycin diazepanone degradation product 43 and allows the assignment of stereochemistry of the natural products as either [C-6'(R), C-2'"(R), C-3'"(R)] or [C-6'(S), C-2'"(S), C-3'"(S)].     

Synthesis of 3'-deoxynucleosides with 2-oxabicyclo[3.1.0]hexane sugar moieties: addition of difluorocarbene to a 3',4'-unsaturated uridine derivative and 1,2-dihydrofurans derived from D- and L-xylose1

Syntheses of 3'-deoxy analogues of adenosine, cytidine, and uridine with a 2,2-difluorocyclopropane ring fused at C3'-C4' are described. Treatment of a 2',5'-protected-3',4'-unsaturated derivative of uridine with difluorocarbene [generated from (CF3)2Hg and NaI] gave a diastereomeric mixture of the 3',4'-difluoromethylene compounds (alpha-L-arabino/beta-D-ribo, approximately 5:4). The limited stereoselectivity for addition at the beta face results from competitive steric hindrance by an allylic 4-methoxybenzyloxy group at C2' on the alpha face and a homoallylic nucleobase at C1' on the beta face. Protected uracil derivatives were converted into their cytosine counterparts via 4-(1,2,4-triazol-1-yl) intermediates. Treatment of 1,2-dihydrofurans derived from D- and L-xylose with difluorocarbene resulted in stereospecific addition at the beta face (anti to the 1,2-O-isopropylidene group on the alpha face). Glycosylations with activated enantiomeric sugar derivatives with the fused difluorocyclopropane ring on the beta face gave protected adenine nucleosides, whereas attempted glycosylation with an alpha-fused derivative gave multiple products. Removal of base- and sugar-protecting groups gave new difluoromethylene-bridged nucleoside analogues.     

Addition of difluorocarbene to 4',5'-unsaturated nucleosides: synthesis and deoxygenation reactions of difluorospirocyclopropane nucleosides

Synthetic routes to 4'-(2,2-difluorospirocyclopropane) analogues of adenosine, cytidine, and uridine are described. Treatment of 2',3'-O-isopropylidene-4',5'-unsaturated compounds derived from adenosine and uridine with difluorocarbene (generated from PhHgCF3 and NaI) gave diastereomeric mixtures of the 2,2-difluorospirocyclopropane adducts. Stereoselectivity resulting from hindrance by the isopropylidene group favored addition at the beta face. Removal of base and sugar protecting groups gave new difluorospirocyclopropane nucleoside analogues. The protected uridine analogue was converted into its cytidine counterpart via a 4-(1,2,4-triazol-1-yl) intermediate. Stannyl radical-mediated deoxygenation of the 3'-O-TBS-2'-thionocarbamate derivatives gave the 2'-deoxy products of direct hydrogen transfer. In contrast, identical treatment of the 2'-O-TBS-3'-thionocarbamate isomers resulted in opening of the vicinal difluorocyclopropane ring upon generation of a C3' radical followed by homoallylic hydrogen transfer to give 4'-(1,1-difluoroethyl)-3',4'-unsaturated nucleoside derivatives. Structural aspects and biological effect considerations are discussed.     

A Stereoselective Approach to β-l-Arabino Nucleoside Analogues: Synthesis and Cyclization of Acyclic 1',2'-synN,O-Acetals

Reported herein is a novel and versatile strategy for the stereoselective synthesis of unnatural β-l-arabinofuranosyl nucleoside analogues from acyclic N,OTMS-acetals bearing pyrimidine and purine bases. These unusual acetals undergo a C1' to C4' cyclization where the OTMS of the acetal serves as the nucleophile to generate 2'-oxynucleosides with complete retention of configuration at the C1' acetal center. N,OTMS-acetals are obtained diastereoselectively from additions of silylated nucleobases onto acyclic polyalkoxyaldehydes in the presence of MgBr(2)·OEt(2). The strategy reported is addressing important synthetic challenges by providing stereoselective access to unnatural l-nucleosides starting from easily accessible pools of d-sugars and, as importantly, by allowing the formation of the sterically challenging 1',2'-cis nucleosides. A wide variety of nucleoside analogues were synthesized in 7-8 steps from easily accessible d-xylose.     

Synthesis of nucleoside analogues bearing the five naturally occurring nucleic acid bases built on a 2-oxabicylo[3.1.0]hexane scaffold

Hitherto unknown nucleoside analogues incorporating the five naturally occurring nucleic acid bases built on a 2-oxabicyclo[3.1.0]hexane template were synthesized. The synthesis of these new conformationally restricted nucleoside analogues involved the preparation of a suitable sugar precursor bearing the 2-oxabicyclo[3.1.0]hexane scaffold. This sugar was readily obtained from [(3aS,6aS)-2,2-dimethyl-3a,6a-dihydrofuro[2,3-d][1,3]dioxol-5-yl]methyl benzyl ether (4) following a Simons-Smith-type cyclopropanation reaction. Finally, glycosylation reactions and deprotection provided the nucleoside analogues. Using nucleoside 14 bearing thymine base as a model, we found that the conformation of such nucleoside analogue was restricted toward a (0)T(1) conformation.     

Synthesis and Anti-HIV Activity of Triazolo-fused 3',4'-Cyclic and 4'-Spiro Nucleoside Analogues

Triazolo-fused 3',4'-cyclic nucleoside 4'-spiro nucleoside analogues were synthesized by an intramolecular 1,3-dipolar cycloaddition of 4'-azido nucleoside derived azido-alkynes in a regio- and stereo-specific manner. The thymine nucleoside base in these target compounds was transformed into the corresponding 5-methyl cytosine component. The synthesized com­pounds were examined in an MAGI(multinuclear-activation galactosidase indicator) assay for exploring the anti-HIV activity and in a H9 T(human T lymphocytes H9) assay for measuring the cell toxicity.     

Stereoselective synthesis and conformational study of novel 2',3'-Didehydro-2',3'-dideoxy-4'-selenonucleosides

Stereoselective synthesis of novel 2',3'-didehydro-2',3'-dideoxy-4'-selenonucleosides (4'-seleno-d4Ns) 4a- c was accomplished via 4'-selenoribofuranosyl pyrimidines 11a- c, as key intermediates. 4'-Selenoribofuranosyl pyrimidines 11a- c were efficiently synthesized from d-ribose or d-gulonic gamma-lactone using a Pummerer-type condensation as a key step. Introduction of 2',3'-double bond was achieved by treating cyclic 2',3'-thiocarbonate with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine.     

Addition of difluorocarbene to 3',4'-unsaturated nucleosides: synthesis of 2'-deoxy analogues with a 2-oxabicyclo[3.1.0]hexane framework

Treatment of protected 2'-deoxy-3',4'-unsaturated nucleosides derived from adenosine and uridine with difluorocarbene [generated from bis(trifluoromethyl)mercury and sodium iodide] gave fused-ring 2,2-difluorocyclopropane compounds. Stereoselective alpha-face addition to the dihydrofuran ring resulted from hindrance by the protected beta-anomeric nucleobases. A protected uracil compound was converted smoothly into the cytosine derivative via a 4-(1,2,4-triazol-1-yl) intermediate. Removal of the protecting groups gave new difluorocyclopropane-fused nucleoside analogues. The solid-state conformation of the nearly planar furanosyl ring in the uracil compound had a shallow 2E pucker, and a more pronounced 1E conformation was present in the furanosyl ring of the cytosine derivative.     

2',3'-双脱氢-2',3'-双脱氧胸苷(d4T)5'-硫代磷酰氨基酸酯的合成和谱学分析

HIV逆转录酶是治疗艾滋病的有效靶点，核苷-磷酰氨基酸酯是HIV逆转录酶的 有效抑制剂，但是这类化合物容易在体内被核酸酶水解。本研究设计合成了对核酸 酶具有抵抗作用的2',3'-双脱氢-2',3'-双脱氧胸苷5'-硫代磷酰氨基酸酯化合物， 这类化合物可以有效地透过细胞膜经过细胞激酶的作用，进入HIV逆转录酶的作用 位点，病毒实验表明该类化合物对MT-4细胞具有较好的抗HIV病毒活性。报道了2', 3'-双脱氢-2',3'-双脱氧胸苷5'-硫代磷酰氨基酸酯化合物的合成，及利用NMR， IR和ESI-MS谱进行的结构表征和构象分析。