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.     

Synthesis of pyrimidine 2'-deoxy ribonucleosides branched at the 2'-position via radical atom-transfer cyclization reaction with a vinylsilyl group as a radical-acceptor tether

Recently, we developed a regio- and stereoselective method for introducing a vinyl group at the position beta to a hydroxyl group in halohydrins or alpha-phenylselenoalkanols via a radical atom-transfer cyclization reaction with a vinylsilyl group as a temporary connecting radical-acceptor tether. The synthesis of 2'-deoxy-2'-C-vinyl- and 2'-deoxy-2'-C-hydroxymethyluridines (7 and 8, respectively) and the corresponding 2'-deoxycytidine congeners (10 and 11, respectively), which were designed as potential antitumor and/or antiviral agents, was achieved using this radical atom-transfer cyclization as the key step. When the 2'-deoxy-2'-iodo-5'-O-monomethoxytrityl (MMTr) uridine derivative 19a, bearing a vinylsilyl group at the 3'-hydroxyl group, was heated with (Me(3)Sn)(2) and AIBN in benzene, the corresponding radical atom-transfer product was generated, which in turn was successively treated with tetrabutylammonium fluoride and TBSCl/imidazole to give the desired 2'-deoxy-5'-O-MMTr-3'-O-TBS-2'-C-vinyluridine (25). Compound 25 was successfully converted into the target 2'-deoxy-2'-branched pyrimidine ribonucleosides 7, 8, 10, and 11.     

Novel bicyclic nucleoside analogue (1S,5S,6S)-6- hydroxy-5-hydroxymethyl-1-(uracil-1-yl)-3,8-dioxabicyclo[3.2.1]octane: synthesis and incorporation into oligodeoxynucleotides

The novel bicyclic nucleoside (1S,5S,6S)-6-hydroxy-5-hydroxymethyl-1-(uracil-1-yl)-3,8-dioxabicyclo[3.2.1]octane [2'-deoxy-1'-C,4'-C-(2-oxapropano)uridine] (15), expected to be restricted into an O4'-endo furanose conformation, was synthesized from the known 1-(3'-deoxy-beta-D-psicofuranosyl)uracil 5. The phosphoramidite derivative of 15 was successfully incorporated into oligodeoxynucleotides using standard methods, and thermal denaturation studies showed moderate decreases in duplex stabilities of -2.1 and -1.5 degrees C per modification toward complementary DNA and RNA, respectively.     

Synthesis of acyclic bis-vinyl pyrimidines: a general route to d4T via metathesis

Unsaturated acyclic pyrimidine analogues, 1-{1-[1-(hydroxymethyl)prop-2-enyloxy]prop-2-enyl}uracil, 1-{1-[1-(hydroxymethyl)prop-2-enyloxy]prop-2-enyl}thymine and 1-{1-[1-(hydroxymethyl)prop-2-enyloxy]prop-2-enyl}cytosine having two asymmetric carbon atoms have been prepared in good yield starting from uridine and 5-methyluridine. The bis-vinyl thymine derivative underwent ring closure metathesis to give d4T, thus providing a novel synthesis of this compound.     

Synthetic studies towards the tunicamycins and analogues based on diazo chemistry. Total synthesis of tunicaminyl uracil

A synthetic approach to the tunicamycins, a complex family of nucleosides with potent antibiotic and antiviral activities is reported based on diazo chemistry. The corresponding precursors for the synthesis of tunicaminyl uracil derivatives, the non-stabilized diazo derived from 13 and the aldehyde derivative of uridine, compound 4, were prepared efficiently from commercially available D-galactal and uridine, respectively. After a high yielding coupling reaction to obtain the ketone 14, a stereoselective reduction provided the corresponding tunicaminyl uracil derivative 17a and its C-7 epimer 17b. The interconversion of the diazo and aldehyde functional groups in the requisite building blocks was similarly achieved to obtain the ketone 32, which after reduction yielded the corresponding 7-deoxy-6-hydroxy tunicaminyl uracil analogs 33a and 33b.     

A highly stereoselective samarium diiodide-promoted aldol reaction with 1'-phenylseleno-2'-keto nucleosides. Synthesis of 1'alpha-branched uridine derivatives

Since 1'-branched nucleosides are biologically important targets in medicinal chemistry, more efficient methods for preparing them are required. The 1'alpha-branched uridine derivatives were successfully synthesized via a samarium diiodide (SmI(2))-promoted aldol reaction. Treatment of the 1'alpha-phenylseleno-2'-ketouridine derivative 6, readily prepared from uridine, with SmI(2) at -78 degrees C in THF reductively cleaved the anomeric Se-C bond to generate the corresponding samarium enolate, which was highly stereoselectively condensed with aldehydes, such as PhCHO, MeCHO, i-PrCHO, or (CH(2)O)(n)(), to give the corresponding 1'alpha-1' 'S-branched products 12a-d. This is the first time an enolate has been generated by reductively cleaving a C-Se bond. The highly selective stereochemical results suggest that the aldol reaction proceeds via a chelation-controlled transition state. When an excess of aldehyde was used and the reaction mixture was gradually warmed, the tandem aldol-Tishchenko reaction proceeded to give the "arabino-type" nucleosides 14a-c, having a 2'-"up" hydroxyl and 1'alpha-1' 'S-branched chain. 1'alpha-Hydroxymethyluridine (21), which is the uracil version of the antitumor antibiotic angustmycin C, was synthesized from the aldol reaction product 10.     

Stereospecific syntheses of 3'-deuterated pyrimidine nucleosides and their site-specific incorporation into DNA

[reaction: see text] 2'-Deoxy-3'-deutero pyrimidines have been synthesized in high yields and incorporated into deoxyoligonucleotides using standard phosphoramidite chemistry. A key synthetic step is a stereospecific reduction of 3'-keto nucleosides using sodium triacetoxyborodeuteride to give 3'-deuterated thymidine and 2'-deoxy uridine nucleosides. Conversion of the corresponding phorphoramidites 7a and 7b to 4-triazolo derivatives has, for the first time, enabled incorporation of 2'-deoxy-3'-deutero cytidine and 2'-deoxy-3'-deutero-5-methyl cytidine into oligonucleotides.     

Lithiation at the 6-position of uridine with lithium hexamethyldisilazide: crucial role of temporary silylation

Lithium hexamethyldisilazide (LiHMDS) can mediate silylation at the 6-position of uridine, although LiHMDS alone is not able to generate the C-6-lithiated uridine. Experimental results showed that temporary silylation of O-4 (or N-3) of the uracil ring triggers the C-6 lithiation with LiHMDS. This finding allowed us to develop an efficient intramolecular alkylation of 5'-deoxy-5'-iodouridine to furnish 6,5'-C-cyclouridine. [reaction--see text]     

Gold-catalyzed cycloisomerization of N-Propargylindole-2-carboxamides: application toward the synthesis of lavendamycin analogues

A series of N-propargylindole-2-carboxamides were found to undergo a AuCl 3-catalyzed cycloisomerization to give beta-carbolinones in high yield. The corresponding beta-chlorocarboline derivative was prepared and used for Pd(0)-catalyzed cross-coupling chemistry directed toward the synthesis of lavendamycin analogues.     

Synthesis of 1-(2′-O-methyl-β-d-ribofuranosyl)-uracil (2′-O-methyluridine) and 3-(2′-O-methyl-β-d-ribofuranosyl)uracil

1-O-Acetyl-3,5-di-O-benzoyl-2-O-methyl-β-d-ribofuranose has been prepared in five steps from benzyl 2-O-methyl-β-d-ribopyranoside. Reaction of the furanose derivative with 2,4-bis-(trimethylsilyl)uracil in the presence of stannic chloride provides a new synthesis of 2′-O-methyl uridine and also yields the hitherto unknown 3-(2′-O-methyl-β-d-ribofuranosyl)uracil.     

beta-Selective synthesis of 2'-deoxy-5,6-dihydro-4-thiouridine, a precursor of the unstable nucleoside product of ionising radiation damage 2'-deoxy-5,6-dihydrocytidine

4-Thio oxathiaphosphepane nucleosides - undergo a rearrangement in pyridine that leads selectively to the beta anomer of the 2'-deoxy-5,6-dihydro-4-thiouridine derivative . This diastereoselective reaction proceeds through a multistep mechanism initiated by the addition of pyridine at the C1'position of - and concomitant opening of the oxathiaphosphepane. This was confirmed by the trapping of the corresponding intermediate in the closely related DMAP series. In contrast, LR thiation of in pyridine leads to a new class of modified nucleosides containing an oxathiaphospholane moiety. The quantitative conversion of into the corresponding 5,6-dihydrocytosine derivative with NH3-MeOH is also reported.     

The chemistry of 4-pyrimidinones: Acetylation and ring-opening reactions

4(3H)-Pyrimidinone, as well as its 5-acetoxy and 5-methoxy derivatives, undergoes selective acetylation at N-1 when treated with acetic anhydride. In the presence of water, these 1-acetylpyrimidines undergo spontaneous covalent hydration at C-2 and cleavage of the 1,2-bond to give crystalline cis-3-acetylamino-N-formyl-acrylamides, generally in good yield. In contrast, the 6-methyl derivative of 4(3H)-pyrimidinone forms an equilibrium mixture of acetylated products that undergo the ring opening process to only a very limited extent, the major product (11%) being the 3-formylamino-N-acetylacrylamide derivative formed via N-3 acetylation and cleavage of the 2,3-bond.     

Benzothiazoline derivatives. II. Preparation of N-substituted derivatives of 2-benzothiazolinethione by thiation of the 2-oxo analogs

Thuiation of the benzoate and acetate esters of 3-(2-hydroxyethyl)-2-benzothiazolinone (Ig) gave the corresponding thiones. The benzoate was then deblocked to yield 3-(2-hydroxyethyl)-2-benzothiazolinethione (Ik), a compound not accessible by direct addition or substitution. Attempts to introduce a chlorine (or bromine) atom in place of the hydroxy 1 group in the latter compound or its S-isomer, 2-(2-hydroxyethylthio)benzothiazole (11a), gave 2,3-dihydrothiazolo-[2,3-b ] benzothiazolium chloride (or bromide) (IIIa or b). The latter compound undergoes dihydrothiazolo ring opening when treated with sodium hydroxide or sodium sulfide to give bis[2-(2-benzolhiazolinon-,3-yl)ethyl]disulfide (IVc) or bis[2-(2-benzothiazolinethion-3-yl)ethyl] disulfide (lVb),respectively. 2-Benzothiazolinethione reacted with ethylenimine and with N-phenylethylenimine to give S-substituted derivatives. Addition to vinyl n-butyl ether gave the expected N-substituted derivative, which was found to undergo removal of the butyoxyethyl group when subjected to conventional conditions for ether cleavage.     

含腺嘌呤的杯芳烃衍生物的合成、表征及其对核苷碱基的分子识别性质

设计合成了一种新型含腺嘌呤基的杯芳烃衍生物(AC)5,11,17,23-四叔丁基-25, 27-二羟基-26-[1-(9-腺嘌呤)-丙氧基]-28-溴丙氧基杯芳烃, 通过红外光谱、元素分析、核磁共振谱和电喷雾质谱等手段对其进行了表征,确认为目标产物; 并采用紫外分光光度法研究了AC的分子识别作用, 通过测定AC与不同浓度、不同组分的核苷、碱基混合体系的吸光度, 证明了AC对尿嘧啶、尿苷具有分子识别作用, 能从其它核苷或碱基共存的体系中将尿苷或尿嘧啶识别出来.     

Synthesis of the phosphoramidite derivative of 2'-deoxy-2'-C-beta-methylcytidine

2'-Deoxy-2'-C-beta-methylnucleosides elicit interest as potential therapeutic agents and as analogues for the analysis of nucleic acid structure and function. An efficient route for the synthesis of 2'-deoxy-2'-C-methyluridine (11), 2'-deoxy-2'-C-methylcytidine (12), and the phosphoramidite derivative of 2'-deoxy-2'-C-beta-methylcytidine (10, 46% overall yield) from 1,2,3,5-tetra-O-benzoyl-2-C-beta-methylribofuranose (1) is described.     

Chemo‐Enzymatic Synthesis of 3‐Deoxy‐β‐D‐ribofuranosyl Purines

9‐(3‐Deoxy‐β‐D ‐erythro‐pentofuranosyl)‐2,6‐diaminopurine ( 6 ) was synthesized by an enzymatic transglycosylation of 2,6‐diaminopurine ( 2 ) with 3′‐deoxycytidine ( 1 ) as a donor of 3‐deoxy‐D ‐erythro‐pentofuranose moiety. This transformation comprises i) deamination of 1 to 3′‐deoxyuridine ( 3 ) under the action of whole cell (E. coli BM‐11) cytidine deaminase (CDase), ii) the phosphorolytic cleavage of 3 by uridine phosphorylase (UPase) giving rise to the formation of uracil ( 4 ) and 3‐deoxy‐α‐D ‐erythro‐pentofuranose‐1‐O‐phosphate ( 5 ), and iii) coupling of the latter with 2 catalyzed by whole cell (E. coli BMT‐4D/1A) purine nucleoside phosphorylase (PNPase). Deamination of 6 by adenosine deaminase (ADase) gave 3′‐deoxyguanosine ( 7 ). Treatment of 6 with NaNO₂ afforded 9‐(3‐deoxy‐β‐D ‐erythro‐pentofuranosyl)‐2‐amino‐6‐oxopurine (3′‐deoxyisoguanosine; 8 ). Schiemann reaction of 6 (HF/HBF₄+NaNO₂) gave 9‐(3‐deoxy‐β‐D ‐erythro‐pentofuranosyl)‐2‐fluoroadenine ( 9 ).     

Steric fixation of bromovinyluracil: Synthesis of furo[2,3-d]pyrimidine nucleosides

A new synthetic procedure for the preparation of 5,6-dihydrofuro[2,3-d]pyrimidin-2(3H)-one ( 3 ) and its deoxyriboside 8 is reported. Compound 3 undergoes nucleophilic reactions with various agents to yield 5-substituted uracil derivatives. The dehydro derivative of 3 , furo[2,3-d]pyrimidin-2(3H)-one ( 18 ) was synthesized by cyclization of BVU 15 , which made us develop a reproducible and high yield method for the synthesis of BV(D)U. Starting from 18 , the α-deoxyriboside 20 and the β-riboside 22 were prepared.     

Synthesis of Novel Nucleic Acid Mimics via the Stereoselective Intermolecular Radical Coupling of 3'-Iodo Nucleosides and Formaldoximes(1)

A highly convergent free radical coupling of alkyl iodides and oximes, mediated by bis(trimethylstannyl) benzopinacolate (8), has been utilized to prepare a series of dimeric nucleosides as mimics of natural nucleic acids. The systematic optimization of the reaction conditions allowed for the single-step conversion of the appropriate iodides and oximes into the 2'-deoxy dimers 9 in moderate to excellent yields. For example, the reaction of 3'-deoxy-3'-iodo-5'-(triphenylmethyl)thymidine (6a) with 3'-O-(tert-butyldiphenylsilyl)-5'-O-(methyleneimino)thymidine (7a) in the presence of 8 in degassed benzene gave an 81% yield of 3'-de(oxyphosphinico)-3'-(methyleneimino)-5'-O-(triphenylmethyl)thymidylyl-(3'-->5')-3'-O-(tert-butyldiphenylsilyl)thymidine (9a). Similarly prepared were dimers containing both pyrimidine (thymine, 5-methylcytosine) and purine (adenine, guanine) bases. The reaction was highly stereoselective, giving only a single dimeric species having the ribo-configuration of the newly introduced C-3'-branched methylene moiety. Also prepared were dimers 16, incorporating 2'-O-methyl ribonucleosides in both halves of the dimer. This required the synthesis of 3'-deoxy-3'-iodo-2'-O-methyl nucleosides 12 as well as 2'-O-methyl-5'-O-methyleneimino nucleosides 15. For example, 5'-O-(tert-butyldiphenylsilyl)-3'-deoxy-3'-iodo-2'-O-methyl-5-methyluridine (12e) was prepared in 80% yield by displacement of the corresponding triflate with Bu(4)NI. Also prepared were the suitably protected 3'-deoxy-3'-iodo adenosine and guanosine derivatives. Compounds 15 were prepared in high yield by a regioselective Mitsunobu reaction to give the corresponding 5'-O-phthalimido nucleosides 13, which were subsequently converted to the requisite oximes 15. In the 2'-O-methyl series, the pinacolate coupling reaction proceeded with efficiency equal to that observed for the 2'-deoxy series 9, but with slightly less stereoselectivity, giving predominantly the C-3'ribo products 16, contaminated with 5-25% of the epimeric material. Mixed base dimers containing both pyrimidine and purine bases at all possible positions, including purine-purine dimers were prepared. The hydroxylamine or methyleneimino (MI) backbone of several representative dimers so prepared was converted via methylation to give the corresponding methylenemethylimino (MMI)-linked compounds, which are novel phosphate surrogates for use in antisense oligonucleotides.     

PHOTOCHEMICAL REDUCTION OF 5-BROMOURACIL BY CYSTEINE DERIVATIVES AND COUPLING OF 5-BROMOURACIL TO CYSTINE DERIVATIVES

Irradiation of pH 7, aqueous solutions of 5-bromouracil (BU) in the presence of cysteine peptide-like derivatives at 308 nm using a XeCl excimer laser yielded initial formation of only uracil (U) and the corresponding cystine derivative. Continued irradiation yielded an S-uracilylcysteinyl adduct as well as additional U and cystine derivative. Similar irradiation of a solution of BU and a cystine derivative yielded initial formation of U and the S-uracilylcysteinyl adduct. Formation of these products as well as secondary products of uracil photochemistry was observed upon irradiation of the respective solutions with 254 nm light. With 308 nm laser excitation, U-Cys adduct formation and reduction of BU to U are proposed to occur via initial electron transfer from the disulfide of the cystine derivative to triplet BU. The quantum yield of BU destruction with 308 nm excitation in the presence of cystine derivative is 1.1 X 10(-3). Reaction of triplet BU with the cysteine derivative does not yield U-Cys adduct but U and cystine derivative. A possible byproduct of reduction of triplet BU to U by a cysteinyl residue in a protein BU-DNA complex is a sulphenyl bromide which might yield a protein-DNA crosslink via nucleophilic substitution on sulfur by a nucleophilic site in DNA.     

用层析法分离磷酸酯基化学修饰的二核苷酸的非对映异构体

本文报道用高效液相色谱法和高效薄层色谱法分离磷酸醌基化学修饰的二核苷酸二尿苷硼烷磷酸酯，二胸苷硫代磷酸酯，二（２＇－脱氧－２＇－氟）尿苷及胞苷硫代磷酸酯的非对映异构体，所得到的非对映异构体的ＲＦ值和＾３１Ｐ－ＮＭＲ化学移植之间的关系符合一般规律，即移动快的异构体有较高的位移植，移动慢的异构体有较的化学位移植。